Thursday, October 13, 2011

Spring 3.1.0.RC1 - JPA EntityManagerFactory bootstrapping without persistence.xml

This will be a quick post. Today Spring 3.1.0.RC1 has been released. See here. This article will take a quick look on one of the enhancements in Spring 3.1:

3.1.12 JPA EntityManagerFactory bootstrapping without persistence.xml

In standard JPA, persistence units get defined through META-INF/persistence.xml files in specific jar files which will in turn get searched for @Entity classes. In many cases, persistence.xml does not contain more than a unit name and relies on defaults and/or external setup for all other concerns (such as the DataSource to use, etc). For that reason, Spring 3.1 provides an alternative: LocalContainerEntityManagerFactoryBean accepts a 'packagesToScan' property, specifying base packages to scan for @Entity classes. This is analogous to AnnotationSessionFactoryBean's property of the same name for native Hibernate setup, and also to Spring's component-scan feature for regular Spring beans. Effectively, this allows for XML-free JPA setup at the mere expense of specifying a base package for entity scanning: a particularly fine match for Spring applications which rely on component scanning for Spring beans as well, possibly even bootstrapped using a code-based Servlet 3.0 initializer.

Source: New Features and Enhancements in Spring 3.1

Here's my existing configuration:

	<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
	p:persistenceXmlLocation="classpath*:META-INF/persistence.xml"
	p:persistenceUnitName="hibernatePersistenceUnit"
	p:dataSource-ref="jpaDataSource"
	p:jpaVendorAdapter-ref="hibernateVendor"/>

	<bean id="hibernateVendor" class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"
	p:showSql="false"/>

view raw fragment-with-persistence.xml hosted with ❤ by GitHub

This requires an extra META-INF/persistence.xml to make it work:

	<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0">
	<persistence-unit name="hibernatePersistenceUnit" transaction-type="RESOURCE_LOCAL">
	<properties>
	<property name="hibernate.hbm2ddl.auto" value="update" />
	<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/>
	</properties>
	</persistence-unit>
	</persistence>

view raw persistence.xml hosted with ❤ by GitHub

How do we improve this?

Based on the docs, we can remove the persistence.xml altogether. But how do we declare the extra configurations related to our ORM? And how does the entityManagerFactory know where our entities are?

Here's how:
1. Delete the META-INF/persistence.xml

2. Declare a packagesToScan property

3. Declare a jpaPropertyMap

Here's the final configuration:

	<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
	p:packagesToScan="org.krams.tutorial.domain"
	p:dataSource-ref="jpaDataSource"
	p:jpaVendorAdapter-ref="hibernateVendor"
	p:jpaPropertyMap-ref="jpaPropertyMap"/>

	<util:map id="jpaPropertyMap">
	<entry key="hibernate.hbm2ddl.auto" value="update"/>
	<entry key="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/>
	</util:map>

	<bean id="hibernateVendor" class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"
	p:showSql="false"/>

view raw fragment-no-persistence.xml hosted with ❤ by GitHub

If you want to try this with an actual project, you either create a new one, or you can play with my demo project Spring MVC: Integrating MySQL, MongoDB, RabbitMQ, and AJAX which has a Github repo.

That's all folks!

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Sunday, October 9, 2011

Tomcat: Clustering and Load Balancing with HAProxy under Ubuntu 10.04 - Part 2

Review

In the previous section, we've set-up a simple environment containing a clustered Tomcat instances and HAProxy for load balancing. In this section, we will test our load balancing environment and explore various strategies to improve our setup.

Setting-up the Environment
- Download Tomcat
- Configure Tomcat
- Run Tomcat
- Download HAProxy
- Configure HAProxy
Load Balancing
- Default Setup
- Sharing Sessions
- Configure Tomcat to Share Sessions
- Retest Session Sharing
- Session Sharing Caveat
- Sharing Sessions
HAProxy Configuration
- Configuration File
- Logging

Load Balancing

Default Setup

After downloading and installing Tomcat and HAProxy, we will now test the default load balancing

Open a browser and visit the following link:

http://localhost/

It should display the following page:

Notice we did not indicate any port. By default the browser will use port 80 for HTTP requests. The previous link is equivalent to:

http://localhost:80/

This means HAProxy is able to redirect our requests from port 80 to the Tomcat instances. If we check the HAProxy logs, we can see that the requests is redirected to tomcat1:

localhost haproxy[4530]: 127.0.0.1:42377 [06/Oct/2011:07:50:57.054] http-in servers/tomcat1 0/0/0/2/28421 200 25030 - - --NN 0/0/0/0/0 0/0 "GET / HTTP/1.1"

Let's pretend that tomcat1 has failed by shutting it down manually. To shutdown tomcat1, run the following command:

sudo /usr/local/tomcat-7.0.21-server1/bin/shutdown.sh

HAProxy's stats page should display that tomcat1 is dead. To display the stats page, open a browser, and visit the following link:

http://localhost/admin?stats

Now, let's check if we can still access the main page. Open a browser and visit the previous link:

http://localhost/

You should see the following page:

Notice the web page is still available! It means HAProxy is able to redirect our request from an inactive server to an active one.

If we check the HAProxy logs, it shows that our request has been redirected to tomcat2:

localhost haproxy[4530]: 127.0.0.1:56619 [06/Oct/2011:07:58:17.761] http-in servers/tomcat2 17/0/0/2/27825 200 13075 - - --NN 0/0/0/0/0 0/0 "GET / HTTP/1.1"

Let's turn off tomcat2. This means all our servers are down! Visit the localhost page again, and we should get the following response:

The web page is down! HAProxy's stat page shows that the Backend servers are down:

Sharing Sessions

If we are serving a web page that holds session information we assume that information is still available regardless if tomcat1 or tomcat2 is down.

Imagine a shopping cart. You're selecting items in a page. Behind the scenes the server you're working at has crashed. You expect the original shopping cart information is still intact. Otherwise, you'll start again from scratch.

Let's verify this behavior by examining the sample applications within the Tomcat examples directory. These examples are built-in to Tomcat when we initially installed it.

Before we proceed, please make sure your environment is as follows:


Server	Status
Tomcat 1	Down
Tomcat 2	Up

The open up a browser, and visit the following page:

http://localhost/examples/jsp/jsp2/simpletag/hello.jsp

This is what you should see:

This application is one of the built-in examples included in the Tomcat installation. In my computer, this application resides at:

/usr/local/tomcat-7.0.21-server1/webapps/examples

I'm going to examine the session ID returned by this page by using Google Chrome's Developer Tools (see http://code.google.com/chrome/devtools/). Here's an actual screenshot:

The session ID reads 697E0084595762C85952E2AFEB7B56FD. If you're running this guide with an actual Tomcat, your session ID will vary.

Now, let's change our environment. Before we proceed, make sure this is your environment:


Server	Status
Tomcat 1	Up
Tomcat 2	Down

Open up a browser, and visit the following page again:

http://localhost/examples/jsp/jsp2/simpletag/hello.jsp

It should display the same page still. Let's examine the session ID returned by this second request:

The session ID reads E501914ABC8DD2F2EC82A4B5123B51AA in the Response Header section; whereas it reads 697E0084595762C85952E2AFEB7B56FD in the Request Header section.

If we refresh the page, the Request Header now has E501914ABC8DD2F2EC82A4B5123B51AA and the original session ID 697E0084595762C85952E2AFEB7B56FD is gone forever. This means when we shutdown tomcat2, the session ID is not transferred from tomcat1.

Although we're seeing the same page, we're actually operating in different sessions. Imagine if this is a shopping cart. Suddenly, all your orders are gone! Time to file a support ticket!

How do we resolve this issue? The solution is simple. Enable session sharing. How? We follow the instructions given in the Apache Tomcat 7' Clustering/Session Replication HOW-TO reference.

Configure Tomcat to Share Sessions

The key to enable session sharing is to declare two XML elements: one in your application's web.xml (1) and the other in Tomcat's server.xml (2):

1. <distributable>
2. <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster">

Let's declare those two XML elements in our "Hello World SimpleTag Handler" example. It's important that we declare those two elements in all our Tomcat instances where our application resides.

Let's do that now.

1. Go to your Tomcat 1's directory, and find the examples directory. In my computer, the directory is:

/usr/local/tomcat-7.0.21-server1/webapps/examples

2. Under WEB-INF, open web.xml and declare a <distributable> element. Place it just above the filter elements. See screenshot below:

3. Next, edit the server.xml. In my computer, this translates to

/usr/local/tomcat-7.0.21-server1/conf

Declare a <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"> element.
Place this element just below the Engine element. See screenshot below:

We've configured tomcat1. Now, configure tomcat2 by repeating the same steps.

Retest Session Sharing

After configuring both Tomcat instances, we need to restart them so that the changes will take effect.

Now, update your environment, and make sure it follows this scenario:


Server	Status
Tomcat 1	Down
Tomcat 2	Up

Open a browser and visit the following page:

http://localhost/examples/jsp/jsp2/simpletag/hello.jsp

Using Google Chrome's Developer Tools, the session ID is 16E9D9B83CFF02196DBC794CE3E0AB3D

Update your environment, and make sure it follows this scenario:


Server	Status
Tomcat 1	Up
Tomcat 2	Down

Again, open a browser and visit the following page again:

http://localhost/examples/jsp/jsp2/simpletag/hello.jsp

Using Google Chrome's Developer Tools, the session ID reads 16E9D9B83CFF02196DBC794CE3E0AB3D

Notice we have the same session ID!. This means our session information has been successfully retained and reused across our Tomcat instances.

Session Sharing Caveat

Everything seems fine now. However, I want to emphasize an important requirement with session sharing. To understand what I meant, let's run another built-in example application.

Open a browser, and visit the following page:

http://localhost/examples/jsp/sessions/carts.html

It should display a shopping cart:

Try adding an item. Immediately, an exception will be thrown:

The exception reads:

java.lang.IllegalArgumentException: setAttribute: Non-serializable attribute cart

Why are we getting this error? If we study the Tomcat 7 reference for clustering, we will find the following information:

To run session replication in your Tomcat 7.0 container, the following steps should be completed:

- All your session attributes must implement java.io.Serializable
- Uncomment the Cluster element in server.xml
- Make sure your web.xml has the element

Source: http://tomcat.apache.org/tomcat-7.0-doc/cluster-howto.html

The reference is telling us to ensure that our session attributes are serializable! Based on the error message, our cart is not serializable.

Let's examine the source code of this cart class. You can find the source code within your Tomcat examples folder. In my computer, this translates to:

/usr/local/tomcat-7.0.21-server1/webapps/examples/WEB-INF/classes/sessions/DummyCart.java

Here's the source code:

	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package sessions;

	import java.util.Vector;

	public class DummyCart {
	Vector<String> v = new Vector<String>();
	String submit = null;
	String item = null;

	private void addItem(String name) {
	v.addElement(name);
	}

	private void removeItem(String name) {
	v.removeElement(name);
	}

	public void setItem(String name) {
	item = name;
	}

	public void setSubmit(String s) {
	submit = s;
	}

	public String[] getItems() {
	String[] s = new String[v.size()];
	v.copyInto(s);
	return s;
	}

	public void processRequest() {
	// null value for submit - user hit enter instead of clicking on
	// "add" or "remove"
	if (submit == null \|\| submit.equals("add"))
	addItem(item);
	else if (submit.equals("remove"))
	removeItem(item);

	// reset at the end of the request
	reset();
	}

	// reset
	private void reset() {
	submit = null;
	item = null;
	}
	}

view raw DummyCart.java hosted with ❤ by GitHub

To make this class serializable, we just implement the java.io.Serializable class as follows:

	public class DummyCart implements Serializable {
	Vector<String> v = new Vector<String>();
	String submit = null;
	String item = null;
	...
	}

view raw DummyCart.java hosted with ❤ by GitHub

You can compile this by yourself. Or you can download my patched version of DummyCart.class (click here to download). To use this patch, follow these steps:

Go to your Tomcat examples directory. In my computer this translates to:

/usr/local/tomcat-7.0.21-server/webapps/examples/WEB-INF/classes/sessions/

Replace the old DummyCart.class with the patched version. Alternatively, rename the old one instead of deleting it.
Repeat the previous steps to all your Tomcat instances.
Restart all Tomcat instances.

Let's revisit our shopping cart. Try adding an item. Notice you're now able to add an item without any exceptions.

If we check the HAProxy logs, our request went to tomcat2

http-in servers/tomcat2 890/0/0/6/30760 304 3109 - - --NN 0/0/0/0/0 0/0 "GET /examples/jsp/sessions/carts.html HTTP/1.1"

The session ID is 84061AA7EF1EF6CADE7489113700481E as shown in the Google Developer tool (I have omitted the screenshot).

Let's turn off tomcat2 and add a new item in the shopping cart.

You should be able to add a new item:

HAProxy logs show that we're now using tomcat1 instance:

http-in servers/tomcat1 0/0/0/35/34234 200 2924 - - --IN 0/0/0/0/0 0/0 "GET /examples/jsp/sessions/carts.jsp?item=Switch+blade&submit=add HTTP/1.1"

Our session ID is still 84061AA7EF1EF6CADE7489113700481E as shown in the Google Developer tool:

Try switching servers off and on. Just make sure there's at least one server running. Notice the session ID never changes.

Next Section

We've successfully implemented load balancing using HAProxy and session sharing among our Tomcat instances. We've learned how to troubleshoot session IDs by using Google Chrome's Developer Tools. In the next secion, we will configure HAProxy logging so that we can easily troubleshoot problems arising from this tool. Click here to proceed.

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Tomcat: Clustering and Load Balancing with HAProxy under Ubuntu 10.04 - Part 1

Introduction

In this article we will explore how to setup a simple Tomcat cluster and load balancing using HAProxy. Our environment will consists of two Tomcat (latest version) instances running under Ubuntu Lucid (10.04 LTS). We will use sample applications from the built-in Tomcat package to demonstrate various scenarios. Later in the tutorial, we will study in-depth how to configure HAProxy and how to setup logging.

What is HAProxy?

HAProxy is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications. It is particularly suited for web sites crawling under very high loads while needing persistence or Layer7 processing - http://haproxy.1wt.eu/

What is Tomcat?

Apache Tomcat is an open source software implementation of the Java Servlet and JavaServer Pages technologies... Apache Tomcat powers numerous large-scale, mission-critical web applications across a diverse range of industries and organizations - http://tomcat.apache.org/

Setting-up the Environment
- Download Tomcat
- Configure Tomcat
- Run Tomcat
- Download HAProxy
- Configure HAProxy
Load Balancing
- Default Setup
- Sharing Sessions
- Configure Tomcat to Share Sessions
- Retest Session Sharing
- Session Sharing Caveat
- Sharing Sessions
HAProxy Configuration
- Configuration File
- Logging

Frequently Asked Questions (FAQ)

Q: Why is this tutorial in Linux instead of Windows?
A: By default the source code and pre-compiled binaries for HAProxy is tailored for Linux/x86 and Solaris/Sparc.

Q: Why Ubuntu 10.04 instead of another Linux distribution?
A: My local machine is running Ubuntu 10.04 LTS.

Q: How do I install HAProxy in Windows?
A: You can install it via Cygwin. Check this link for more info.

An Overview

Before we start with actual configuration and development, let's get a visual overview of the whole setup. The diagram below depicts our simple load balancing architecture and the typical flow of data:

1. A client visits our website.
2. HAProxy receives the request and performs load balancing.
3. Request is redirected to a Tomcat instance.
4. Response is returned back to HAProxy and back to the client.

Notice in the backend we are sharing the same IP address (127.0.0.1), the localhost. This is useful for testing purposes, but in production we will normally assign each server in its own machine with its own IP address.

Since we have three servers that share the same IP address, we have to assign different ports to each as follows:


Server	Port
HAProxy	80
Tomcat 1	8080
Tomcat 2	8090

The client should only have access to the IP address and port where HAProxy resides. If we let the client bypass HAProxy by directly connecting to any of the Tomcat instances, then we have defeated the purpose of load balancing.

Requirements

When this article was written, the environment and tools I'm using are as follows:


Name	Version	Official Site
HAProxy	Stable 1.4.18	http://haproxy.1wt.eu/
Tomcat	7.0.22	http://tomcat.apache.org/
Ubuntu	10.04	http://www.ubuntu.com/

The HAProxy and Tomcat versions are the latest stable versions as of this writing (Oct 9 2011). This tutorial should work equally well on Tomcat 6. For the operating system, I recommend Ubuntu 10.04 because that's where I tested and setup this tutorial. In any case, you should be able to apply the same steps to your favorite Linux distro. For Windows users, use Cygwin instead (see FAQs).

Setting-up the Environment

To ensure we're on the same page, I'm providing a walkthrough for configuring and installing of Tomcat and HAProxy. We will test a basic setup to verify that we have setup our environment correctly.

Download Tomcat

To download Tomcat visit its official page. Alternatively, you can visit this link directly: http://tomcat.apache.org/download-70.cgi

Select a core binary distribution. For my system, I opted for the zip version (the first option).

Extract the download to your file system. In my case, I extracted the zip file to /usr/local and rename the extracted folder to tomcat-7.0.21-server1.

Copy and paste this folder to the same location /usr/local and rename the folder to tomcat-7.0.21-server2. The final result should be similar to the following:

Your Tomcats are installed.

Configure Tomcat

If we examine the server.xml inside the Tomcat conf folder, we will discover that Tomcat uses the following ports by default:

Tomcat Default Ports
Element	Port
Shutdown	8005
HTTP Connector	8080
AJP Connector	8009

We have two Tomcat instances. If we run both, we'll encounter a port conflict since both instances are using the same port numbers. To resolve this conflict we will edit one of the server.xml files. In our case, we will choose Tomcat instance 2.

Go to tomcat-7.0.21-server2/conf and open-up server.xml. Find the following lines and replace them accordingly:

	1. Modify shutdown port from
	<Server port="8005" shutdown="SHUTDOWN">

	to

	<Server port="8105" shutdown="SHUTDOWN">

	2. Modify HTTP port from
	<Connector port="8080" protocol="HTTP/1.1"
	connectionTimeout="20000"
	redirectPort="8443" />

	to

	<Connector port="8180" protocol="HTTP/1.1"
	connectionTimeout="20000"
	redirectPort="8443" />

	3. Modify AJP port from
	<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

	to

	<Connector port="8109" protocol="AJP/1.3" redirectPort="8443" />

view raw server2.xml hosted with ❤ by GitHub

Save the changes. At the end, your Tomcat instances should be configured as follows:

Tomcat 1 & 2 Ports
	Tomcat 1 Ports	Tomcat 2 Ports
Shutdown	8005	8105
HTTP Connector	8080	8180
AJP Connector	8009	8109

Run Tomcat

After configuring our Tomcat installations, let's run them and verify that they're running according to the specified ports.

Tomcat 1
Since I'm using Ubuntu, I can run Tomcat 1 by issuing the following command in the terminal:

sudo /usr/local/tomcat-7.0.21-server1/bin/startup.sh

If in case you get a permission error, make the startup.sh executable first. To verify that Tomcat 1 is running, open-up a browser and visit the following link:

http://localhost:8080

Here's the resulting page:

Tomcat 2
To run Tomcat 2, follow the same steps earlier. This time we'll execute the following command:

sudo /usr/local/tomcat-7.0.21-server2/bin/startup.sh

Open another browser and visit the following link:

http://localhost:8180

Here's the resulting page:

We've successfully setup two Tomcat instances. Next, we will download and setup HAProxy.

Download HAProxy

To download HAProxy, visit its official page and download either the pre-compiled binaries or the source. Alternatively, you can install via apt-get (however if you want the latest version, you might need to tinker with sources.list to update your sources).

For this tutorial, we will build and compile from the source (which I believe is faster and simpler).

Open up a terminal and enter the following commands:

	$ wget http://haproxy.1wt.eu/download/1.4/src/haproxy-1.4.18.tar.gz
	$ tar -zxf haproxy-1.4.18.tar.gz
	$ cd haproxy-1.4.18
	$ make install

view raw make-haproxy-1.4.18 hosted with ❤ by GitHub

This should download the latest HAProxy, extract, and install it. If you get a permission error, make sure to prepend a sudo in each command. If you have difficulty installing from the source, I suggest you do some Googling on this topic. There are plenty of resources on how to install HAProxy from the source (albeit some are outdated though but may still apply).

After HAProxy has been installed, verify that it's indeed installed! Open up a terminal and type the following command: haproxy.

You should see the following message:

Configure HAProxy

In order for HAProxy to act as a load balancer, we need to create a custom HAProxy configuration file where we will declare our Tomcat servers.

I'll present you first a basic configuration to jump-start our exposure to HAProxy. In part 3, we'll study this configuration and explain what's happening per line.

I created a configuration file and saved it at /etc/haproxy/haproxy.cfg:

	global
	log 127.0.0.1 local0
	log 127.0.0.1 local1 notice
	maxconn 4096
	daemon

	defaults
	log global
	mode http
	option httplog
	option dontlognull
	retries 3
	option redispatch
	maxconn 2000
	contimeout 5000
	clitimeout 50000
	srvtimeout 50000

	frontend http-in
	bind *:80
	default_backend servers

	backend servers
	option httpchk OPTIONS /
	option forwardfor
	stats enable
	stats refresh 10s
	stats hide-version
	stats scope .
	stats uri /admin?stats
	stats realm Haproxy\ Statistics
	stats auth admin:pass

	cookie JSESSIONID prefix
	server tomcat1 127.0.0.1:8080 cookie JSESSIONID_SERVER_1 check inter 5000
	server tomcat2 127.0.0.1:8180 cookie JSESSIONID_SERVER_2 check inter 5000

view raw haproxy hosted with ❤ by GitHub

Run HAProxy

After configuring HAProxy, let's verify that it's running and communicating properly with our Tomcat instances.

Open up a terminal and run the following command:

sudo haproxy -f /etc/haproxy/haproxy.cfg

Now open up a browser and visit the following link:

http://localhost/admin?stats

Your browser should show the following page:

Based on this page, tomcat1 and tomcat2 are both down. That's because they are not running yet. Let's run both Tomcat instances, and the stats page should automatically update.

To start tomcat1, run the following command:

sudo /usr/local/tomcat-7.0.21-server1/bin/startup.sh

To start tomcat2, run the following command:

sudo /usr/local/tomcat-7.0.21-server2/bin/startup.sh

Here's the result:

Notice both Tomcats are now ready.

Next Section

We've completed setting-up our environment for Tomcat clustering and load balancing using HAProxy. In the next section, we will explore various load balancing scenarios to learn more about Tomcat and HAProxy. Click here to proceed.

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Tomcat: Clustering and Load Balancing with HAProxy under Ubuntu 10.04 - Part 3

Review

In the previous section, we've implemented load balancing using HAProxy and session sharing among our Tomcat instances. In this section, we will examine in-depth the HAProxy configuration file and setup its logging facilities.

Setting-up the Environment
- Download Tomcat
- Configure Tomcat
- Run Tomcat
- Download HAProxy
- Configure HAProxy
Load Balancing
- Default Setup
- Sharing Sessions
- Configure Tomcat to Share Sessions
- Retest Session Sharing
- Session Sharing Caveat
- Sharing Sessions
HAProxy Configuration
- Configuration File
- Logging

HAProxy Configuration

When it comes to HAProxy configuration, the best source of information is its online documentation at http://haproxy.1wt.eu/#docs. It's one massive text file of technical information though.

Configuration File

Not all information in that document applies to our configuration. Therefore, I have copied the relevant information only and pasted them as comments per line:

	global
	log 127.0.0.1 local0
	log 127.0.0.1 local1 notice
	#Adds a global syslog server. Up to two global servers can be defined. They
	#will receive logs for startups and exits, as well as all logs from proxies
	#configured with "log global". An optional level can be specified to filter
	#outgoing messages. By default, all messages are sent.

	#An IPv4 address optionally followed by a colon and a UDP port. If
	#no port is specified, 514 is used by default (the standard syslog port).

	maxconn 4096
	#Sets the maximum per-process number of concurrent connections to <number>. It
	#is equivalent to the command-line argument "-n". Proxies will stop accepting
	#connections when this limit is reached. The "ulimit-n" parameter is
	#automatically adjusted according to this value. See also "ulimit-n"

	uid 99
	#Changes the process' user ID to <number>. It is recommended that the user ID
	#is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
	#be started with superuser privileges in order to be able to switch to another
	#one. See also "gid" and "user".

	gid 99
	#Changes the process' group ID to <number>. It is recommended that the group
	#ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
	#be started with a user belonging to this group, or with superuser privileges.
	#See also "group" and "uid".

	daemon
	#Makes the process fork into background. This is the recommended mode of
	#operation. It is equivalent to the command line "-D" argument. It can be
	#disabled by the command line "-db" argument.

	#debug
	#NO NEED TO ENABLE - krams
	#Enables debug mode which dumps to stdout all exchanges, and disables forking
	#into background. It is the equivalent of the command-line argument "-d". It
	#should never be used in a production configuration since it may prevent full
	#system startup.

	#quiet
	#NO NEED TO ENABLE - krams
	#Do not display any message during startup. It is equivalent to the command-
	#line argument "-q".

	defaults
	log global
	#Enable per-instance logging of events and traffic.
	#global should be used when the instance's logging parameters are the
	#same as the global ones. This is the most common usage. "global"
	#replaces <address>, <facility> and <level> with those of the log
	#entries found in the "global" section. Only one "log global"
	#statement may be used per instance, and this form takes no other
	#parameter.

	mode http
	#Set the running mode or protocol of the instance
	#The instance will work in HTTP mode. The client request will be
	#analyzed in depth before connecting to any server. Any request
	#which is not RFC-compliant will be rejected. Layer 7 filtering,
	#processing and switching will be possible. This is the mode which
	#brings HAProxy most of its value.

	option httplog
	#Enable logging of HTTP request, session state and timers

	option dontlognull
	#Enable or disable logging of null connections

	retries 3
	#Set the number of retries to perform on a server after a connection failure

	option redispatch
	#Enable or disable session redistribution in case of connection failure

	maxconn 2000
	#Fix the maximum number of concurrent connections on a frontend
	#This value should not exceed the global maxconn

	contimeout 5000
	#Set the maximum time to wait for a connection attempt to a server to succeed.

	clitimeout 50000
	#Set the maximum inactivity time on the client side.
	#An unspecified timeout results in an infinite timeout, which
	#is not recommended. Such a usage is accepted and works but reports a warning
	#during startup because it may results in accumulation of expired sessions in
	#the system if the system's timeouts are not configured either.

	srvtimeout 50000
	#Set the maximum inactivity time on the server side.

	#balance roundrobin
	#NO NEED TO ENABLE. IT'S THE DEFAULT - krams
	#The load balancing algorithm of a backend is set to roundrobin when no other
	#algorithm, mode nor option have been set

	frontend http-in
	bind *:80
	#Define one or several listening addresses and/or ports in a frontend

	default_backend servers
	#Specify the backend to use when no "use_backend" rule has been matched

	backend servers
	option httpchk OPTIONS /
	#Enable HTTP protocol to check on the servers health

	option forwardfor
	#Enable insertion of the X-Forwarded-For header to requests sent to servers
	#Since HAProxy works in reverse-proxy mode, the servers see its IP address as
	#their client address. This is sometimes annoying when the client's IP address
	#is expected in server logs. To solve this problem, the well-known HTTP header
	#"X-Forwarded-For" may be added by HAProxy to all requests sent to the server.

	stats enable
	#Enable statistics reporting with default settings

	stats refresh 10s
	#Enable statistics with automatic refresh

	stats hide-version
	#Enable statistics and hide HAProxy version reporting

	stats scope .
	# Enable statistics and limit access scope

	stats uri /admin?stats
	#Enable statistics and define the URI prefix to access them

	stats realm Haproxy\ Statistics
	#Enable statistics and set authentication realm
	#<realm> is the name of the HTTP Basic Authentication realm reported to
	#the browser. The browser uses it to display it in the pop-up
	#inviting the user to enter a valid username and password.

	stats auth admin:pass
	#Enable statistics with authentication and grant access to an account

	cookie JSESSIONID prefix
	#Enable cookie-based persistence in a backend
	#server <name> <address>[:port] [param*]
	#Please refer to section 5 for more details.

	server tomcat1 127.0.0.1:8080 cookie JSESSIONID_SERVER_1 check inter 5000
	server tomcat2 127.0.0.1:8180 cookie JSESSIONID_SERVER_2 check inter 5000
	#Declare a server in a backend
	#server <name> <address>[:port] [param*]
	#<param*> is a list of parameters for this server. The "server" keywords
	#accepts an important number of options and has a complete section
	#dedicated to it. Please refer to section 5 for more details.

view raw haproxy.cfg hosted with ❤ by GitHub

Take note of the following parts:

frontend http-in: We're telling HAProxy to listen to HTTP requests
default_backend servers: We declare a set of backend servers
stats uri /admin?stats: This is the URL to the stats page, relative to your hostname
stats realm Haproxy\ Statistics: This is the server name you see when you login to the stats page.
server tomcat1 127.0.0.1:8080 cookie JSESSIONID check inter 5000: Defines a server. In this case, a Tomcat server. Here we assigned the IP and port number.

HAProxy Logging

Logging is crucial in any serious application, and HAProxy has facilities to log its activities.
However, to setup one requires extra effort because to enable logging in HAProxy we need to know
Linux's logging facilities via the Syslog server and take into account the Syslog implementation in Ubuntu Lucid (10.04).

What is Syslog?

syslog is a utility for tracking and logging all manner of system messages from the merely informational to the extremely critical. Each system message sent to the syslog server has two descriptive labels associated with it that makes the message easier to handle. - Source: Quick HOWTO : Ch05 : Troubleshooting Linux with syslog

To enable logging, we need to:

Add a logging facility in haproxy.cfg
Add the logging facility to Syslog server

Add a logging facility in haproxy.cfg
Edit the haproxy.cfg file:

sudo gedit /etc/haproxy/haproxy.cfg

And declare the following:

	global
	log 127.0.0.1 local0
	log 127.0.0.1 local1 notice

view raw haproxy.cfg hosted with ❤ by GitHub

We declared two logging facilities under the global section. Both facilities will send their log output to the Syslog server which is located at 127.0.0.1. The default port is 514. Each logger has its own unique name: local0 and local1.

Why are they named such? These are local facilities defined by the user to log specific deamons (see What is LOCAL0 through LOCAL7 ?).

Remember an optional level can be specified to a filter. Hence, local1 has an extra argument: notice. This means local1 will only capture logs with notice level as opposed to all, i.e. errors, debugs.

Reload haproxy by running the following command:

sudo haproxy -f /etc/haproxy/haproxy.cfg -p /var/run/haproxy.pid -sf $(cat /var/run/haproxy.pid)

This command will not restart HAProxy. It will just reload the configuration file. This is good because you won't be killing active connections. If you get a missing file i.e /var/run/haproxy.pid or other errors, just kill the haproxy process and restart it:

kill -9 #####

where ##### is the process id

Add the logging facility to Syslog server
There are two solutions to achieve this.

Solution #1
a. Run

sudo gedit /etc/rsyslog.conf

And declare the following lines at the end:

	# Custom log facilities for haproxy
	local0.* /var/log/haproxy0a.log
	local1.* /var/log/haproxy1a.log

	$ModLoad imudp
	# load the imudp module for rsyslog
	# provides UDP syslog reception

	# start UDP server on this port, "*" means all addresses
	$UDPServerRun 514

	# local IP address (or name) the UDP listens should bind to
	$UDPServerAddress 127.0.0.1

view raw rsyslog.conf hosted with ❤ by GitHub

b. Restart syslog server by running:

restart rsyslog

Solution #2
Instead of editing directly the rsyslog.conf, we can declare a separate configuration under /etc/rsyslog.d/ directory. If you inspect carefully the rsyslog.conf, you will see the following comments:

	#
	# Include all config files in /etc/rsyslog.d/
	#
	$IncludeConfig /etc/rsyslog.d/*.conf

view raw rsyslog.conf hosted with ❤ by GitHub

This setting will load all *.conf files under /etc/rsyslog.d/ directory.

a. Run

sudo gedit /etc/rsyslog.d/haproxy.conf

And declare the following lines at the end:

	# Custom log facilities for haproxy
	local0.* /var/log/haproxy0a.log
	local1.* /var/log/haproxy1a.log

	$ModLoad imudp
	# load the imudp module for rsyslog
	# provides UDP syslog reception

	# start UDP server on this port, "*" means all addresses
	$UDPServerRun 514

	# local IP address (or name) the UDP listens should bind to
	$UDPServerAddress 127.0.0.1

view raw haproxy.conf hosted with ❤ by GitHub

b. Restart syslog server by running:

restart rsyslog

Overflowing Logs

We've setup HAProxy logging. We can see the logs in /var/log/haproxy0a.log and /var/log/haproxy1a.log files. However, we also see them in /var/log/syslog.

This is bad because now we have redundant logs that just eats up space. You don't want that syslog to be polluted with HAProxy logs. That's the reason why we've setup a separate logging facility in the first place.

There are two ways to prevent this unwanted overflow:

Solution #1
1. Run

sudo gedit /etc/rsyslog.d/50-default.conf

And search for the following lines (right after the introductory comments):

	auth,authpriv.* /var/log/auth.log
	.;auth,authpriv.none -/var/log/syslog

view raw 50-default.conf hosted with ❤ by GitHub

And change them as follows:

	auth,authpriv.* /var/log/auth.log
	.;auth,authpriv,local0,local1.none -/var/log/syslog

view raw 50-default.conf hosted with ❤ by GitHub

This means local0 and local1 should not overflow to syslog.

b. Restart syslog server by running:

restart rsyslog

Solution #2
1. Run

sudo gedit /etc/rsyslog.conf

And find the following lines:

	# Custom log facilities for haproxy
	local0.* /var/log/haproxy0a.log
	local1.* /var/log/haproxy1a.log

view raw rsyslog.conf hosted with ❤ by GitHub

And change them as follows:

	# Custom log facilities for haproxy
	local0.* -/var/log/haproxy0a.log
	& ~
	local1.* -/var/log/haproxy1a.log
	& ~

view raw rsyslog.conf hosted with ❤ by GitHub

The addition of & ~ will prevent the logs designated to local0 from overflowing to other logging facilities.

Note: If you can't find those lines, maybe you've declared your configuration under /etc/rsyslog.d/haproxy.conf. If yes, follow the same steps.

b. Restart syslog server by running:

restart rsyslog

Rotate Logs

We've setup HAProxy logging. We've isolated the logs from overflowing to syslog. However, there's another problem. The HAProxy logs will soon pile-up and consume precious disk space. Gladly, Linux has a way to schedule and reuse the same lgo file and perform compression.

For more info of log rotation in Linux, please see Quick HOWTO : Ch05 : Troubleshooting Linux with syslog: Logrotate.

Again, there are two ways of handling this requirement:

Solution #1
a. Run

sudo gedit /etc/logrotate.d/haproxy

And add the following lines:

	/var/log/haproxy*.log
	{
	rotate 4
	weekly
	missingok
	notifempty
	compress
	delaycompress
	sharedscripts
	postrotate
	reload rsyslog >/dev/null 2>&1 \|\| true
	endscript
	}

view raw logrotate.d hosted with ❤ by GitHub

b. Restart syslog server by running:

restart rsyslog

Solution #2
Log rotation with rsyslog from the official rsyslog documentation. This is something I haven't tried yet but if you're willing to experiment, here's the link: http://www.rsyslog.com/doc/log_rotation_fix_size.html. This technique utilizes the output channels.

However, read the following notes:

Output Channels are a new concept first introduced in rsyslog 0.9.0. As of this writing, it is most likely that they will be replaced by something different in the future. So if you use them, be prepared to change you configuration file syntax when you upgrade to a later release.
- http://www.rsyslog.com/doc/rsyslog_conf_output.html

References

The following is a compendium of references that I found interesting to read further:

R: What is LOCAL0 through LOCAL7 ?
L: http://www.linuxquestions.org/questions/linux-security-4/what-is-local0-through-local7-310637/

R: Quick HOWTO : Ch05 : Troubleshooting Linux with syslog
L: http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch05_:_Troubleshooting_Linux_with_syslog

R: rsyslog official site
L: http://www.rsyslog.com/doc/rsyslog_conf.html

R: rsyslog.conf configuration file
L: http://www.rsyslog.com/doc/rsyslog_conf.html

R: UDP Syslog Input Module
L: http://www.rsyslog.com/doc/imudp.html

R: How to keep haproxy log messages out of /var/log/syslog
L: http://serverfault.com/questions/214312/how-to-keep-haproxy-log-messages-out-of-var-log-syslog

R: HAProxy Logging in Ubuntu Lucid
L: http://kevin.vanzonneveld.net/techblog/article/haproxy_logging/

Q: Install and configure haproxy, the software based loadbalancer in Ubuntu
A: http://linuxadminzone.com/install-and-configure-haproxy-the-software-based-loadbalancer-in-ubuntu/

Conclusion

That's it. We've completed our study of HAProxy and Tomcat clustering. We've learned how to setup, configure load balancing, and handle failover. We've also learned the important points when enabling session sharing. We've also studied HAProxy's configuration and logging facilities.

If you want to learn more about web development and integration with other technologies, feel free to read my other tutorials in the Tutorials section.

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Friday, September 16, 2011

Spring MVC: Integrating MySQL, MongoDB, RabbitMQ, and AJAX - Part 1

Introduction

In this article we will explore how to integrate MySQL, MongoDB, and RabbitMQ in a Spring MVC application using Spring Data JPA, Spring Data MongoDB, and Spring AMQP projects respectively. Then we'll add AJAX in the presentation layer using jQuery. For presenting tabular data, we will explore two jQuery plugins: DataTables and jQgrid. The jQgrid version will use Spring Cache support to boost performance. The ultimate purpose of this article is to demonstrate how to integrate these different projects in a single Spring MVC application.

Our application is a simple event management system for performing CRUD operations. When we talk of events, we're referring to the colloquial definition, i.e wedding event. The application's main data will be stored in a MySQL database using Hibernate as our ORM. We will use Spring Data JPA to simplify the data access layer. This means we don't need to implement our own data access objects.

Our application is also capable of broadcasting these events as simple text messages. To broadcast these events, we will use RabbitMQ as our messaging broker, and Spring AMQP for sending and receiving of messages.

No application is free from errors. Therefore, we've added error persistence capability using MongoDB. Our application has logging capabilities already, but we want the ability to analyze these errors later. Therefore, this is where MongoDB plays in. To simplify the data access layer, we will use Spring Data MongoDB, similar with Spring Data JPA.

Frequently Asked Questions (FAQs)

Q: What is JPA?
A: See http://en.wikipedia.org/wiki/Java_Persistence_API
Q: What is MongoDB?
A: See http://www.mongodb.org
Q: What is RabbitMQ?
A: See http://www.rabbitmq.com
Q: What is Spring Data?
A: See http://www.springsource.org/spring-data
Q: What is Spring Data - JPA?
A: See http://www.springsource.org/spring-data/jpa
Q: What is Spring Data - MongoDB?
A: See http://static.springsource.org/spring-data/data-document/docs/current/reference/html
Q: What is Spring AMQP?
A: See http://www.springsource.org/spring-amqp
Q: What is jQuery?
A: http://jquery.com/
Q: What is AJAX?
A: http://en.wikipedia.org/wiki/Ajax_(programming)
Q: What is Ehcache?
A: http://ehcache.org/

Required Tools and Services

The following tools and services are essential in building and running our project:

MySQL

MySQL: http://www.mysql.com/downloads/
Wamp: http://www.wampserver.com
XAMPP: http://www.apachefriends.org

RabbitMQ

http://www.rabbitmq.com/download.html

MongoDB

http://www.mongodb.org/downloads

Maven

Maven: http://maven.apache.org/download.html
STS: http://www.springsource.com/developer/sts

Screenshots

Before we dive into development, it's better if we first visualize what we will be developing.

Live Deployment in the Cloud

The best way to interact with the application is with a live deployment. Therefore, I have taken extra steps to deploy the project in the cloud via the excellent open platform Cloud Foundry. To access the project, visit http://spring-mysql-mongo-rabbit.cloudfoundry.com/

Project Structure

To see how we're going to structure the project, take a look at the following screenshot:

The project's source code is available at GitHub. You can access the project's repository at spring-mysql-mongo-rabbit-integration

Project Dependencies (pom.xml)

The pom.xml contains the project's dependencies. It's a long list but I will only show the relevant entries. As of Sept 17 2011, we're using the latest versions.

What is POM?

POM stands for "Project Object Model". It is an XML representation of a Maven project held in a file named pom.xml. See http://maven.apache.org/pom.html

	<!-- Versions -->
	<properties>
	<spring.version>3.1.0.M1</spring.version>
	<spring.data.jpa.version>1.1.0.M1</spring.data.jpa.version>
	<spring.data.mongo.version>1.0.0.M4</spring.data.mongo.version>
	<spring.amqp.version>1.0.0.RELEASE</spring.amqp.version>
	<org.cloudfoundry-version>0.8.0</org.cloudfoundry-version>
	</properties>

	<dependencies>
	<!-- CloudFoundry -->
	<dependency>
	<groupId>org.cloudfoundry</groupId>
	<artifactId>cloudfoundry-runtime</artifactId>
	<version>${org.cloudfoundry-version}</version>
	</dependency>

	<!-- Spring Core -->
	<dependency>
	<groupId>org.springframework</groupId>
	<artifactId>spring-core</artifactId>
	<version>${spring.version}</version>
	<type>jar</type>
	<scope>compile</scope>
	</dependency>

	<!-- Spring Data JPA -->
	<dependency>
	<groupId>org.springframework.data</groupId>
	<artifactId>spring-data-jpa</artifactId>
	<version>${spring.data.jpa.version}</version>
	</dependency>

	<!-- Spring Data MongoDB -->
	<dependency>
	<groupId>org.springframework.data</groupId>
	<artifactId>spring-data-mongodb</artifactId>
	<version>${spring.data.mongo.version}</version>
	</dependency>

	<!-- Spring RabbitMQ -->
	<dependency>
	<groupId>org.springframework.amqp</groupId>
	<artifactId>spring-rabbit</artifactId>
	<version>${spring.amqp.version}</version>
	</dependency>
	...
	...
	</dependencies>

view raw pom(snippet).xml hosted with ❤ by GitHub

To see the pom's entire contents, please check the attached Maven project at the end of this tutorial.

Development

The project will be divided into four parts:

Event Management
Messaging support
Error persistence
Build and deploy

A. Event Management

The Event Management is the core function of the system. And we're specifically referring to the CRUD operations. We will divide this stage in four sub-parts:

Event Management
- A1. Domain
- A2. Service
- A3. Controller
- A4. View
  1. DataTables view
  2. jQgrid view
- A5. Crosscutting Concerns

A1. Domain

The domain contains a simple Event class. By marking it with @Entity the class will be persisted in a relational database. Notice the class has validation constraints added. For example, the name field cannot be null.

Special attention is given to the date field. We've annotated it with @DateTimeFormat, a Spring conversion annotation (see Spring Reference 5.6.2.1 Format Annotation API) to help us serialize and deserialize JSON dates in the presentation layer.

Event.java

	package org.krams.tutorial.domain;

	import java.util.Date;

	import javax.persistence.Entity;
	import javax.persistence.GeneratedValue;
	import javax.persistence.Id;
	import javax.validation.constraints.NotNull;
	import org.springframework.format.annotation.DateTimeFormat;
	import org.springframework.format.annotation.DateTimeFormat.ISO;

	/**
	* A simple Event class.
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	@Entity
	public class Event {

	@Id
	@GeneratedValue
	private Long id;

	@NotNull(message="Name: Please enter name of event")
	private String name;

	private String description;

	@NotNull(message="Participants: Please enter number of participants")
	private Integer participants;

	@NotNull(message="Date: Please enter a date")
	@DateTimeFormat(iso=ISO.DATE_TIME)
	private Date date;

	public Long getId() {
	return id;
	}
	public void setId(Long id) {
	this.id = id;
	}
	public String getName() {
	return name;
	}
	public void setName(String name) {
	this.name = name;
	}
	public String getDescription() {
	return description;
	}
	public void setDescription(String description) {
	this.description = description;
	}
	public Integer getParticipants() {
	return participants;
	}
	public void setParticipants(Integer participants) {
	this.participants = participants;
	}
	public Date getDate() {
	return date;
	}
	public void setDate(Date date) {
	this.date = date;
	}
	@Override
	public String toString() {
	return "Event [id=" + id + ", name=" + name + ", description="
	+ description + ", participants=" + participants + ", date="
	+ date + "]";
	}
	}

view raw Event.java hosted with ❤ by GitHub

A2. Service

Before we start developing the service layer we need to create first the data access objects (DAOs) manually. We do this for every new project. Through time it becomes repetitive and tedious. Gladly, Spring has a solution: the Spring Data project.

Spring Data's purpose is to provide us ready-made data access objects for various database sources. All we need to do is extend an interface and we're good to go. This means we can start writing the service immediately (if needed).

Spring Data is not a single project, but rather it's composed of many different projects specifically catering to different types of databases (see http://www.springsource.org/spring-data). Since we're using MySQL and Hibernate we will use the Spring Data JPA project.

IEventRepository.java

	package org.krams.tutorial.repository.jpa;

	import org.krams.tutorial.domain.Event;
	import org.springframework.data.jpa.repository.JpaRepository;

	/**
	* A repository for {@link Event}
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	public interface IEventRepository extends JpaRepository<Event, Long> {
	}

view raw IEventRepository.java hosted with ❤ by GitHub

IEventService.java

	package org.krams.tutorial.service;

	import java.util.List;

	import org.krams.tutorial.domain.Event;

	/**
	* Service interface for {@link Event}
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	public interface IEventService {

	public Event create(Event event);

	public Event read(Long id);

	public List<Event> readAll();

	public Event update(Event event);

	public Event delete(Long id);

	}

view raw IEventService.java hosted with ❤ by GitHub

EventService.java

	package org.krams.tutorial.service;

	import java.util.List;

	import org.krams.tutorial.domain.Event;
	import org.krams.tutorial.repository.jpa.IEventRepository;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.stereotype.Service;
	import org.springframework.transaction.annotation.Transactional;

	/**
	* Service implementation for {@link Event}
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	@Service
	@Transactional
	public class EventService implements IEventService {

	@Autowired
	private IEventRepository repository;

	public Event create(Event event) {
	return repository.save(event);
	}

	public Event read(Long id) {
	return repository.findOne(id);
	}

	public List<Event> readAll() {
	return repository.findAll();
	}

	public Event update(Event event) {
	Event existingEvent = repository.findOne(event.getId());

	// Assign new values
	existingEvent.setName(event.getName());
	existingEvent.setParticipants(event.getParticipants());
	existingEvent.setDescription(event.getDescription());
	existingEvent.setDate(event.getDate());

	return repository.save(existingEvent);
	}

	public Event delete(Long id) {
	repository.delete(id);

	return repository.findOne(id);
	}
	}

view raw EventService.java hosted with ❤ by GitHub

A3. Controller

We have a single controller, EventController, whose main purpose is to display the Event page. It also has methods for handling CRUD operations that are ultimately delegated to the EventService.

EventController.java

	package org.krams.tutorial.controller;

	import java.util.List;
	import org.krams.tutorial.domain.Event;
	import org.krams.tutorial.dto.ResponseDto;
	import org.krams.tutorial.service.IEventService;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.stereotype.Controller;
	import org.springframework.ui.Model;
	import org.springframework.web.bind.annotation.RequestMapping;
	import org.springframework.web.bind.annotation.RequestMethod;
	import org.springframework.web.bind.annotation.ResponseBody;

	/**
	* Controlling for handling event requests
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	@Controller
	@RequestMapping("/event")
	public class EventController {

	@Autowired
	private volatile IEventService service;

	@RequestMapping
	public String getEventPage() {
	return "event-page";
	}

	@RequestMapping(value = "/add", method = RequestMethod.POST)
	public @ResponseBody ResponseDto<Event> add(Event event) {

	if (service.create(event) != null) {
	return new ResponseDto<Event>(true);
	}

	return new ResponseDto<Event>(false);
	}

	@RequestMapping(value = "/edit", method = RequestMethod.POST)
	public @ResponseBody ResponseDto<Event> edit(Event event) {

	if (service.update(event) != null) {
	return new ResponseDto<Event>(true);
	}

	return new ResponseDto<Event>(false);
	}

	@RequestMapping(value = "/delete", method = RequestMethod.POST)
	public @ResponseBody ResponseDto<Event> delete(Long id) {

	if (service.delete(id) == null) {
	return new ResponseDto<Event>(true);
	}

	return new ResponseDto<Event>(false);
	}

	@RequestMapping(value = "/getall", method = RequestMethod.POST)
	public @ResponseBody ResponseDto<Event> getall() {

	List<Event> events = service.readAll();

	if (events != null) {
	return new ResponseDto<Event>(true, events);
	}

	return new ResponseDto<Event>(false);
	}
	}

view raw EventController.java hosted with ❤ by GitHub

A4. View

I've provided two views for displaying Event records: a DataTables version and a jQgrid version. The purpose of having two views is to demonstrate Spring's flexibility and teach various ways of presenting tabular data.

To proceed, please choose your preferred view (a specific guide will be presented):

JMeter Test

The main difference between these two views are the addition of cache to the jQgrid controller. To appreciate the difference, I've provided JMeter tests to gauge each controller's performance. Take note that this tests have nothing to do with the DataTables or jQgrid plugin. The tests are written so that it will only query the controllers without generating the presentation layer.

Small dataset (9 records):

Large dataset (4300+ records):

Notice in small datasets the difference in performance is almost trivial. However, in large datasets the difference is phenomenal. Adding a cache greatly improves the application's performance (of course this assumes that the same request will be called multiple times).

Click here to download the JMeter Test. To run this test, make sure to run only one test, i.e do the DataTables first, then the jQgrid, or vice versa.

What is JMeter?

Apache JMeter is open source software, a 100% pure Java desktop application designed to load test functional behavior and measure performance. Source: http://jakarta.apache.org/jmeter/

A5. Crosscutting Concerns

As mentioned earlier, no application is free from errors. To facilitate troubleshooting, a logging mechanism needs to be added. Typically we would place the logging mechanism across our existing classes. This is a crosscutting concern.

What is a crosscutting concern?

In computer science, cross-cutting concerns are aspects of a program which affect other concerns. These concerns often cannot be cleanly decomposed from the rest of the system in both the design and implementation, and can result in either scattering (code duplication), tangling (significant dependencies between systems), or both.

For instance, if writing an application for handling medical records, the bookkeeping and indexing of such records is a core concern, while logging a history of changes to the record database or user database, or an authentication system, would be cross-cutting concerns since they touch more parts of the program. See http://en.wikipedia.org/wiki/Cross-cutting_concern

To implement a clean way of logging our application, we will take advantage of Spring's CustomizableTraceInterceptor support as seen in the Spring Data JPA reference (Appendix B. Frequently asked questions).

By default CustomizableTraceInterceptor uses trace level for logging. If we want to change the logging level, we need to extend this class and override the writeToLog() method. We have created a sub-class TraceInterceptor and change the logging level to debug

TraceInterceptor.java

	package org.krams.tutorial.aop;

	import org.aopalliance.intercept.MethodInvocation;
	import org.apache.commons.logging.Log;
	import org.apache.log4j.Logger;
	import org.springframework.aop.interceptor.CustomizableTraceInterceptor;
	import org.springframework.core.annotation.Order;

	/**
	* Extends {@link CustomizableTraceInterceptor} to provide custom logging levels
	*
	*/
	public class TraceInterceptor extends CustomizableTraceInterceptor {

	private static final long serialVersionUID = 287162721460370957L;
	protected static Logger logger4J = Logger.getLogger("aop");

	@Override
	protected void writeToLog(Log logger, String message, Throwable ex) {
	if (ex != null) {
	logger4J.debug(message, ex);
	} else {
	logger4J.debug(message);
	}
	}

	@Override
	protected boolean isInterceptorEnabled(MethodInvocation invocation, Log logger) {
	return true;
	}
	}

view raw TraceInterceptor.java hosted with ❤ by GitHub

After creating the class, we declare it as a bean in the XML configuration. Notice we've configured the entry and exit signature patterns and the pointcut expressions to match. In other words, this will log all services and specific controllers.

trace-context.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <beans 	xmlns="http://www.springframework.org/schema/beans"
        	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        	xmlns:p="http://www.springframework.org/schema/p"
        	xmlns:aop="http://www.springframework.org/schema/aop"
        	xsi:schemaLocation="
 			http://www.springframework.org/schema/beans
 			http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
 			http://www.springframework.org/schema/aop
 			http://www.springframework.org/schema/aop/spring-aop-3.1.xsd">
 	<!-- Cross-cutting Concerns-->
 	<!-- For parsing classes with @Aspect annotation -->
 	<aop:aspectj-autoproxy/>
 	<!-- See http://static.springsource.org/spring-data/data-jpa/docs/current/reference/html/#faq -->
 	<!-- See http://idevone.wordpress.com/2009/09/02/howto-simple-profiling-with-spring-aop/ -->
 	<!-- See http://stackoverflow.com/questions/1366354/do-method-profiling-basic-execution-time-with-spring-aop -->
 	<bean id="customizableTraceInterceptor" class="org.krams.tutorial.aop.TraceInterceptor"
 		p:enterMessage="Entering $[targetClassShortName].$[methodName]($[arguments])"
 		p:exitMessage="Leaving $[targetClassShortName].$[methodName](): $[returnValue]"/>
 	<aop:config>
 	  <aop:advisor advice-ref="customizableTraceInterceptor"
 	    pointcut="execution(public * org.krams.tutorial.service..*(..))"/>
 	  <aop:advisor advice-ref="customizableTraceInterceptor"
 	    pointcut="execution(public * org.krams.tutorial.controller.EventController.*(..))"/>
 	  <aop:advisor advice-ref="customizableTraceInterceptor"
 	    pointcut="execution(public * org.krams.tutorial.controller.JqgridEventController.*(..))"/>
 	  <aop:advisor advice-ref="customizableTraceInterceptor"
 	    pointcut="execution(public * org.krams.tutorial.controller.MainController.*(..))"/>
 	</aop:config>
 </beans>

view raw trace-context.xml hosted with ❤ by GitHub

Next Section

In the next section, we will add messaging support using RabbitMQ and Spring AMQP. To proceed to the next section, click here.

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Spring MVC: Integrating MySQL, MongoDB, RabbitMQ, and AJAX - Part 3

Review

In the previous two sections, we've managed to create the core Event management system and integrated RabbitMQ messaging using Spring AMQP. For performing CRUD operations, we've utilized the Spring Data JPA project. In this section, we will integrate MongoDB and add error persistence.

Where am I?

Error Persistence

It might be odd why we need to record errors in the application. Isn't the default logging feature enough? That depends. But for the purpose of this tutorial, we are doing it to explore MongoDB integration. There are also advantages with this approach. We can easily query and analyze our application's errors and provide a statistical view.

It's interesting that logging is the first use case listed in the MongoDB site and statistical analysis as the last well-suited use case (see MongoDB Use Cases).

We'll divide this page into five sections:

C. Error Persistence
- C1. Domain
- C2. Service
- C3. Aspect
- C4. Controller
- C5. View

C1. Domain

The domain contains a simple ErrorLog class. At the class head we've added @Document, a Spring Data MongoDB annotation, for efficiency reasons, and @Id to mark the field id as the class's identifier. If you scrutinize the application's domain classes, notice the @Id annotation in the Event.java (earlier) is from the javax.persistence package; whereas the @Id in ErrorLog.java is from the org.springframework.data.annotation package.

ErrorLog.java

	package org.krams.tutorial.domain;

	import java.io.Serializable;
	import java.util.Date;

	import org.springframework.data.annotation.Id;

	import org.springframework.data.mongodb.core.mapping.Document;

	/**
	* Represents an error log entity
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	@Document
	public class ErrorLog implements Serializable {

	private static final long serialVersionUID = 1326887243102331826L;

	@Id
	private String id;

	private String type;
	private String message;
	private String signature;
	private String arguments;
	private int count;
	private Date dateEncountered;

	public ErrorLog() {
	super();
	}

	public ErrorLog(String type, String message, Date dateEncountered) {
	super();
	this.type = type;
	this.message = message;
	this.count = 1;
	this.dateEncountered = dateEncountered;
	}

	public ErrorLog(String type, String message, Date dateEncountered, String signature, String arguments) {
	super();
	this.type = type;
	this.message = message;
	this.count = 1;
	this.dateEncountered = dateEncountered;
	this.signature = signature;
	this.arguments = arguments;
	}

	public ErrorLog(String type, String message, int count,
	Date dateEncountered) {
	super();
	this.type = type;
	this.message = message;
	this.count = count;
	this.dateEncountered = dateEncountered;
	}

	public ErrorLog(String type, String message, int count,
	Date dateEncountered, String signature, String arguments) {
	super();
	this.type = type;
	this.message = message;
	this.count = count;
	this.dateEncountered = dateEncountered;
	this.signature = signature;
	this.arguments = arguments;
	}

	public String getId() {
	return id;
	}

	public void setId(String id) {
	this.id = id;
	}

	public String getType() {
	return type;
	}

	public void setType(String type) {
	this.type = type;
	}

	public String getMessage() {
	return message;
	}

	public void setMessage(String message) {
	this.message = message;
	}

	public String getSignature() {
	return signature;
	}

	public void setSignature(String signature) {
	this.signature = signature;
	}

	public String getArguments() {
	return arguments;
	}

	public void setArguments(String arguments) {
	this.arguments = arguments;
	}

	public int getCount() {
	return count;
	}

	public void setCount(int count) {
	this.count = count;
	}

	public Date getDateEncountered() {
	return dateEncountered;
	}

	public void setDateEncountered(Date dateEncountered) {
	this.dateEncountered = dateEncountered;
	}

	@Override
	public String toString() {
	return "Error [id=" + id + ", type=" + type + ", message=" + message
	+ ", signature=" + signature + ", arguments=" + arguments
	+ ", count=" + count + ", dateEncountered=" + dateEncountered
	+ "]";
	}
	}

view raw ErrorLog.java hosted with ❤ by GitHub

C2. Service

Normally before we start developing the service layer we have to create first the data access objects (DAOs) manually. It becomes tedious as you keep repeating the same implementation. Gladly, Spring is here to rescue us from this repetitive task with Spring Data project.

Spring Data's main purpose is to provide us ready-made data access objects for various database sources. This means all we need to do is write our service to contain the business logic. And since we're using a MongoDB, we will use the corresponding Spring Data project: Spring Data MongoDB. (To see a list of other Spring Data projects, visit http://www.springsource.org/spring-data).

IErrorLogRepository.java

	package org.krams.tutorial.repository.mongo;

	import org.krams.tutorial.domain.ErrorLog;
	import org.springframework.data.mongodb.repository.MongoRepository;

	/**
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	public interface IErrorLogRepository extends MongoRepository<ErrorLog, String> {
	}

view raw IErrorLogRepository.java hosted with ❤ by GitHub

That's it. We're done with the service. Wait, where's the service? We don't create one since we don't have custom business logic that needs to be wrapped in a service. All we're doing is retrieval of records.

C3. Aspect

Error persistence, at its core, is no different with logging. It's a crosscutting concern. And similar with how we implemented AMQP messaging, we will use an Aspect to add error persistence.

We have declared EventMongoAspect with two pointcut expressions: one for the service and another for the controller. The interceptService() method handles and persists service errors, while the interceptController() method handles controller errors. We don't persist controller errors; instead we provide a default value so that when returning JSP pages we're not propagating stack traces to the browser.

EventMongoAspect.java

	package org.krams.tutorial.aop;

	import java.util.Date;

	import org.apache.log4j.Logger;
	import org.aspectj.lang.ProceedingJoinPoint;
	import org.aspectj.lang.annotation.Around;
	import org.aspectj.lang.annotation.Aspect;
	import org.krams.tutorial.domain.ErrorLog;
	import org.krams.tutorial.domain.Event;
	import org.krams.tutorial.dto.ResponseDto;
	import org.krams.tutorial.repository.mongo.IErrorLogRepository;
	import org.krams.tutorial.util.ErrorUtil;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.core.annotation.Order;
	import org.springframework.stereotype.Component;

	/**
	* Interceptor for persisting {@link Event} errors to MongoDB and
	* handling controller failures by providing default response value
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	@Aspect
	@Order(2)
	@Component
	public class EventMongoAspect {

	protected Logger logger = Logger.getLogger("aop");

	@Autowired
	private IErrorLogRepository errorLogRepository;

	@Around("execution(* org.krams.tutorial.service.EventService.*(..))")
	public Object interceptService(ProceedingJoinPoint pjp) throws Throwable {
	logger.debug(String.format("Processing %s", pjp.getSignature()));

	try {

	return pjp.proceed();

	} catch (Exception e) {
	logger.error("Unable to process method", e);

	logger.debug("Persisting error to MongoDB");
	StringBuilder arguments = new StringBuilder();
	for (Object arg: pjp.getArgs()) {
	arguments.append(arg);
	}

	errorLogRepository.save(new ErrorLog(ErrorUtil.getErrorType(e),
	e.getMessage(),
	new Date(),
	pjp.getSignature().toLongString(),
	arguments.toString()));

	return pjp.proceed();
	}
	}

	/**
	* When a controller method encounters an exception by default the exception is
	* propagated to the browser. It's an ugly sight, specially when dealing with AJAX.
	* To avoid this side-effect, we catch all controller exception and return an Event
	* containing a false value
	*/
	@Around("execution(* org.krams.tutorial.controller.EventController.*(..))")
	public Object interceptController(ProceedingJoinPoint pjp) throws Throwable {
	try {
	return pjp.proceed();
	} catch (Exception e) {
	return new ResponseDto<Event>(false);
	}
	}
	}

view raw EventMongoAspect.java hosted with ❤ by GitHub

C4. Controller

The error controller is a simple controller with the single purpose of serving the error page.

ErrorController.java

	package org.krams.tutorial.controller;

	import java.util.List;

	import org.krams.tutorial.domain.ErrorLog;
	import org.krams.tutorial.dto.ResponseDto;
	import org.krams.tutorial.repository.mongo.IErrorLogRepository;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.stereotype.Controller;
	import org.springframework.web.bind.annotation.RequestMapping;
	import org.springframework.web.bind.annotation.RequestMethod;
	import org.springframework.web.bind.annotation.ResponseBody;

	@Controller
	@RequestMapping("/error")
	public class ErrorController {


	@Autowired
	private IErrorLogRepository errorLogRepository;

	@RequestMapping
	public String getErrorPage() {
	return "error-page";
	}

	@RequestMapping(value = "/getall", method = RequestMethod.POST)
	public @ResponseBody ResponseDto<ErrorLog> getall() {

	List<ErrorLog> errors = errorLogRepository.findAll();

	if (errors != null) {
	return new ResponseDto<ErrorLog>(true, errors);
	}

	return new ResponseDto<ErrorLog>(false);
	}
	}

view raw ErrorController.java hosted with ❤ by GitHub

C5. View

Our view is a single JSP page containing a table and an AJAX request for retrieving records. The setup is similar with the event-page.jsp (see A4. View), except we don't have dialogs for adding, editing, or deleting records.

The getRecords() function is the AJAX request responsible for retrieval and filling-in of records to the table. Then it will convert the table to a DataTables. The addition of DataTables is mainly for aesthetic purposes (and some nifty features like sorting and searching).

error-page.jsp

	<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
	<%@ taglib uri="http://www.springframework.org/tags" prefix="spring" %>
	<%@ page session="false" %>

	<c:url value="/" var="rootUrl"/>
	<c:url value="/resources" var="resourcesUrl"/>

	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>

	<!-- CSS Imports-->
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/jquery/dark-hive/jquery-ui-1.8.6.custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/datatables/custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/main/main.css"/>

	<!-- JS Imports -->
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-1.5.2.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-ui-1.8.12.custom.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/datejs/date.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/datatables/jquery.dataTables.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/util/util.js"></script>

	<title>Errors</title>
	</head>
	<body class="ui-widget-content">

	<div id="menu">
	<ul>
	<li><a href="${rootUrl}event">Events (DataTables)</a></li>
	<li><a href="${rootUrl}jqgrid/event">Events (jQgrid)</a></li>
	<li><a href="${rootUrl}error">Errors</a></li>
	<li><a href="${rootUrl}monitor/event">Monitor Events</a></li>
	<li><a href="${rootUrl}monitor/error">Monitor Errors</a></li>
	</ul>
	<br style="clear:left"/>
	</div>

	<h3 class="title">Errors</h3>
	<table id="errorTable">
	<thead>
	<tr>
	<th></th>
	<th>Type</th>
	<th>Arguments</th>
	<th>Count</th>
	<th>Date</th>
	</tr>
	</thead>
	<tbody>
	</tbody>
	</table>

	<script type="text/javascript">
	// Retrieves all records
	$(function() {
	$.getRecords('#errorTable', '${rootUrl}error/getall',
	['type', 'arguments', 'count', 'dateEncountered'],
	function() {
	$('#errorTable').dataTable( {
	"bJQueryUI": true,
	"sPaginationType": "full_numbers"
	});
	});
	});
	</script>

	</body>
	</html>

view raw error-page.jsp hosted with ❤ by GitHub

Result

You can preview the final output by visiting a live deployment at http://spring-mysql-mongo-rabbit.cloudfoundry.com/error

Next Section

In the next section, we will build and deploy our project using Tomcat and Jetty. To proceed, click here.

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Spring MVC: Integrating MySQL, MongoDB, RabbitMQ, and AJAX - Part 2

Review

In the previous section, we created the core Event management system and utilized the Spring Data JPA project to simplify data access. We've also added AJAX functionality to make the application responsive. In this section, we will integrate RabbitMQ and messaging in general.

Where am I?

Messaging Support

Our application is capable of broadcasting events as simple text messages. These messages are CRUD actions and exceptions that arise during the lifetime of the application. This means if a user performs an add, edit, delete, or get these actions will be published to a message broker. If there are any exceptions, we will also publish them.

Why do we need to publish these events? First, it helps us study and explore RabbitMQ messaging. Second, we can have a third-party application whose sole purpose is to handle these messages for intensive statistical analysis. Third, it allows us to monitor in real-time and check the status of our application instantaneously.

If you're unfamiliar with messaging and its benefits, I suggest visiting the following links:

We'll divide this page into four sections:

B. Messaging Support
- B1. Aspect
- B2. Configuration
- B3. Controller
- B4. View

B1. Aspect

We will publish CRUD operations as simple messages. It's like logging except we send the logs to a message broker. Usually we would add this feature across existing classes. Unfortunately, this leads to "scattering" and " tangling" of code. No doubt--it's a crosscutting concern. We have the same scenario when added the logging feature earlier (See A5. Crosscutting Concerns section earlier).

We have created an Aspect, EventRabbitAspect.java, to solve this concern. To send messages, we use the AmqpTemplate where we pass the exchange, routing key, and the message. Since we want to publish messages as they are called and also errors as they happened, we use @Around to capture these events. The proceeding code is a variation of the original tutorial Chatting in the Cloud: Part 1 by Mark Fisher (http://blog.springsource.com/2011/08/16/chatting-in-the-cloud-part-1/)

EventRabbitAspect.java

	package org.krams.tutorial.aop;

	import java.util.Date;

	import org.apache.log4j.Logger;
	import org.aspectj.lang.ProceedingJoinPoint;
	import org.aspectj.lang.annotation.Around;
	import org.aspectj.lang.annotation.Aspect;
	import org.springframework.amqp.core.AmqpTemplate;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.core.annotation.Order;
	import org.springframework.stereotype.Component;

	/**
	* Interceptor for publishing messages to RabbitMQ
	*
	* @author krams at {@link http://krams915@blogspot.com}
	*/
	@Aspect
	@Order(1)
	@Component
	public class EventRabbitAspect {

	protected Logger logger = Logger.getLogger("aop");

	@Autowired
	private volatile AmqpTemplate amqpTemplate;

	public static final String RABBIT_EXCHANGE = "eventExchange";
	public static final String GENERAL_EVENT_ROUTE_KEY = "event.general.*";
	public static final String ERROR_EVENT_ROUTE_KEY = "event.error.*";

	@Around("execution(* org.krams.tutorial.service.EventService.*(..))")
	public Object interceptService(ProceedingJoinPoint pjp) throws Throwable {

	try {

	logger.debug("Publishing event to RabbitMQ");
	this.amqpTemplate.convertAndSend(RABBIT_EXCHANGE, GENERAL_EVENT_ROUTE_KEY, new Date() + ": " + pjp.toShortString());

	return pjp.proceed();

	} catch (Exception e) {

	logger.debug("Publishing event to RabbitMQ");
	this.amqpTemplate.convertAndSend(RABBIT_EXCHANGE, ERROR_EVENT_ROUTE_KEY, new Date() + ": " + pjp.getSignature().toLongString() + " - " + e.toString());

	return pjp.proceed();
	}
	}
	}

view raw EventRabbitAspect.java hosted with ❤ by GitHub

In order for Spring to recognize this aspect, make sure to declare the following element in your XML configuration (we've done this in the trace-context.xml):

	<!-- For parsing classes with @Aspect annotation -->
	<aop:aspectj-autoproxy/>

view raw trace-context(snippet).xml hosted with ❤ by GitHub

B2. Configuration

After declaring the Aspect, we now declare and configure the RabbitMQ and Spring AMQP specific settings. In fact, you will soon discover that most of the work with Spring AMQP is configuration-related: declaration of queues, bindings, exchanges, and connection settings.

We've declared two queues: eventQueue for normal events, and errorQueue for errors. We have a single exchange, eventExchange where we declare the bindings for the two queues.

In order to send messages to the eventQueue, we set the routing key to event.general.*. Likewise, to send messages to the errorQueue, we set the routing key to event.error.*. For a tutorial on these concepts, please visit the official examples at http://www.rabbitmq.com/getstarted.html

spring-rabbit.xml

	<?xml version="1.0" encoding="UTF-8"?>
	<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:rabbit="http://www.springframework.org/schema/rabbit"
	xmlns:cloud="http://schema.cloudfoundry.org/spring"
	xsi:schemaLocation="
	http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
	http://www.springframework.org/schema/context
	http://www.springframework.org/schema/context/spring-context-3.1.xsd
	http://www.springframework.org/schema/rabbit
	http://www.springframework.org/schema/rabbit/spring-rabbit-1.0.xsd
	http://schema.cloudfoundry.org/spring
	http://schema.cloudfoundry.org/spring/cloudfoundry-spring-0.8.xsd">

	<context:property-placeholder location="/WEB-INF/spring.properties" />

	<rabbit:queue id="eventQueue"/>
	<rabbit:queue id="errorQueue"/>

	<rabbit:topic-exchange name="eventExchange">
	<rabbit:bindings>
	<rabbit:binding queue="eventQueue" pattern="event.general.*"/>
	<rabbit:binding queue="errorQueue" pattern="event.error.*"/>
	</rabbit:bindings>
	</rabbit:topic-exchange>

	<rabbit:template connection-factory="rabbitConnectionFactory" exchange="eventExchange"/>

	<rabbit:admin connection-factory="rabbitConnectionFactory"/>

	<rabbit:listener-container>
	<rabbit:listener queues="eventQueue" ref="monitorController" method="handleEvent"/>
	<rabbit:listener queues="errorQueue" ref="monitorController" method="handleError"/>
	</rabbit:listener-container>

	<bean id="rabbitConnectionFactory" class="org.springframework.amqp.rabbit.connection.CachingConnectionFactory"
	p:username="guest" p:password="guest" p:port="5672">
	<constructor-arg value="localhost" />
	</bean>

	<!-- Cloud-based
	<cloud:rabbit-connection-factory id="rabbitConnectionFactory"/> -->

	</beans>

view raw spring-rabbit.xml hosted with ❤ by GitHub

B3. Controller

After configuring RabbitMQ and Spring AMQP, we declare a controller, aptly named MonitorController. It's main purpose is to handle monitoring requests. This controller is based on Chatting in the Cloud: Part 1 blog by Mark Fisher (http://blog.springsource.com/2011/08/16/chatting-in-the-cloud-part-1/).

MonitorController.java

	package org.krams.tutorial.controller;

	import java.util.Queue;
	import java.util.concurrent.LinkedBlockingQueue;

	import org.springframework.amqp.core.AmqpTemplate;
	import org.springframework.beans.factory.annotation.Autowired;
	import org.springframework.stereotype.Controller;
	import org.springframework.util.StringUtils;
	import org.springframework.web.bind.annotation.RequestMapping;
	import org.springframework.web.bind.annotation.ResponseBody;

	@Controller
	@RequestMapping("/monitor")
	public class MonitorController {

	@Autowired
	private volatile AmqpTemplate amqpTemplate;

	private final Queue<String> eventMessages = new LinkedBlockingQueue<String>();
	private final Queue<String> errorMessages = new LinkedBlockingQueue<String>();

	@RequestMapping(value = "/event")
	public String eventPage() {
	return "event-monitor-page";
	}

	@RequestMapping(value = "/error")
	public String errorPage() {
	return "error-monitor-page";
	}

	@RequestMapping(value = "/event/log")
	@ResponseBody
	public String eventLog() {
	return StringUtils.arrayToDelimitedString(this.eventMessages.toArray(), "<br/>");
	}

	@RequestMapping(value = "/error/log")
	@ResponseBody
	public String errorLog() {
	return StringUtils.arrayToDelimitedString(this.errorMessages.toArray(), "<br/>");
	}

	/**
	* Handles normal event messages.
	* This method is invoked when a RabbitMQ message is received.
	*/
	public void handleEvent(String message) {
	if (eventMessages.size() > 100) {
	eventMessages.remove();
	}
	eventMessages.add(message);
	}

	/**
	* Handles error messages.
	* This method is invoked when a RabbitMQ message is received.
	*/
	public void handleError(String message) {
	if (errorMessages.size() > 100) {
	errorMessages.remove();
	}
	errorMessages.add(message);
	}
	}

view raw MonitorController.java hosted with ❤ by GitHub

B4. View

We have two JSP pages event-monitor-page.jsp and error-monitor-page.jsp for event and error views respectively. We've utilized AJAX to pull information from the application. Again, this is based on Chatting in the Cloud: Part 1 blog by Mark Fisher (http://blog.springsource.com/2011/08/16/chatting-in-the-cloud-part-1/).

event-monitor-page.jsp

	<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
	<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
	<%@ taglib uri="http://www.springframework.org/tags/form" prefix="sf" %>
	<%@ taglib uri="http://www.springframework.org/tags" prefix="spring" %>
	<%@ page session="false" %>

	<c:url value="/" var="rootUrl"/>
	<c:url value="/resources" var="resourcesUrl"/>

	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>

	<!-- CSS Imports-->
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/jquery/dark-hive/jquery-ui-1.8.6.custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/main/main.css"/>

	<!-- JS Imports -->
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-1.5.2.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-ui-1.8.12.custom.min.js"></script>

	<title>Event Monitor</title>
	</head>
	<body class="ui-widget-content">

	<div id="menu">
	<ul>
	<li><a href="${rootUrl}event">Events (DataTables)</a></li>
	<li><a href="${rootUrl}jqgrid/event">Events (jQgrid)</a></li>
	<li><a href="${rootUrl}error">Errors</a></li>
	<li><a href="${rootUrl}monitor/event">Monitor Events</a></li>
	<li><a href="${rootUrl}monitor/error">Monitor Errors</a></li>
	</ul>
	<br style="clear:left"/>
	</div>

	<script type="text/javascript">
	var running = false;
	var timer;
	function load() {
	if (running) {
	$.ajax({
	url : '${rootUrl}monitor/event/log',
	success : function(message) {
	if (message && message.length) {
	var messagesDiv = $('#log');
	messagesDiv.html(message);
	messagesDiv.animate({ scrollTop: messagesDiv.attr("scrollHeight") - messagesDiv.height() }, 150);
	}
	timer = poll();
	},
	error : function() {
	timer = poll();
	},
	cache : false
	});
	}
	}
	function start() {
	if (!running) {
	running = true;
	if (timer != null) {
	clearTimeout(timer);
	}
	timer = poll();
	}
	}
	function poll() {
	if (timer != null) {
	clearTimeout(timer);
	}
	return setTimeout(load, 1000);
	}
	$(function() {
	start();
	});
	</script>

	<h3 class="title">Event Monitor</h3>
	<div id="log" class="monitor"> </div>

	</body>
	</html>

view raw event-monitor-page.jsp hosted with ❤ by GitHub

error-monitor-page.jsp

	<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
	<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
	<%@ taglib uri="http://www.springframework.org/tags/form" prefix="sf" %>
	<%@ taglib uri="http://www.springframework.org/tags" prefix="spring" %>
	<%@ page session="false" %>

	<c:url value="/" var="rootUrl"/>
	<c:url value="/resources" var="resourcesUrl"/>

	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>

	<!-- CSS Imports-->
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/jquery/dark-hive/jquery-ui-1.8.6.custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/main/main.css"/>

	<!-- JS Imports -->
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-1.5.2.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-ui-1.8.12.custom.min.js"></script>

	<title>Error Monitor</title>
	</head>
	<body class="ui-widget-content">

	<div id="menu">
	<ul>
	<li><a href="${rootUrl}event">Events (DataTables)</a></li>
	<li><a href="${rootUrl}jqgrid/event">Events (jQgrid)</a></li>
	<li><a href="${rootUrl}error">Errors</a></li>
	<li><a href="${rootUrl}monitor/event">Monitor Events</a></li>
	<li><a href="${rootUrl}monitor/error">Monitor Errors</a></li>
	</ul>
	<br style="clear:left"/>
	</div>

	<script type="text/javascript">
	var running = false;
	var timer;
	function load() {
	if (running) {
	$.ajax({
	url : '${rootUrl}monitor/error/log',
	success : function(message) {
	if (message && message.length) {
	var messagesDiv = $('#log');
	messagesDiv.html(message);
	messagesDiv.animate({ scrollTop: messagesDiv.attr("scrollHeight") - messagesDiv.height() }, 150);
	}
	timer = poll();
	},
	error : function() {
	timer = poll();
	},
	cache : false
	});
	}
	}
	function start() {
	if (!running) {
	running = true;
	if (timer != null) {
	clearTimeout(timer);
	}
	timer = poll();
	}
	}
	function poll() {
	if (timer != null) {
	clearTimeout(timer);
	}
	return setTimeout(load, 1000);
	}
	$(function() {
	start();
	});
	</script>

	<h3 class="title">Error Monitor</h3>
	<div id="log" class="monitor"> </div>

	</body>
	</html>

view raw error-monitor-page.jsp hosted with ❤ by GitHub

Result

You can preview the final output by visiting our live app at http://spring-mysql-mongo-rabbit.cloudfoundry.com/monitor/event

Next Section

In the next section, we will integrate MongoDB and add error persistence to the current application. To proceed to the next section, click here.

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Spring MVC: Integrating MySQL, MongoDB, RabbitMQ, and AJAX - Part 1: DataTables View

Review

In the previous section, we created the core Event management system. In this section, we will work on the View layer. Data will be presented in a table. We will use DataTables, a jQuery plugin, and a custom JavaScript function to provide advance features to our table like sorting and searching.

Where am I?

DataTables

What is DataTables?

DataTables is a plug-in for the jQuery Javascript library. It is a highly flexible tool, based upon the foundations of progressive enhancement, which will add advanced interaction controls to any HTML table. (Source: http://datatables.net/)

Before we proceed with the development, let's preview the final output:

Development

Since we've already discussed the controller and service classes in the previous section, we just need to discuss the JSP pages. We actually have five JSP pages:

Primary page
Supporting pages

add-dialog.jsp
edit-dialog.jsp
delete-dialog.jsp
generic-dialog.jsp

1. Primary page

The primary page contains the main view. It's a single page containing the following sections:

URLs
Imports
Menu
Table
Dialogs
Conversion of links to buttons
Attaching link functions
Retrieval of records and conversion to DataTables

event-page.jsp

	<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
	<%@ taglib uri="http://www.springframework.org/tags" prefix="spring" %>
	<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>

	<c:url value="/" var="rootUrl"/>
	<c:url value="/resources" var="resourcesUrl"/>

	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>

	<!-- CSS Imports-->
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/jquery/dark-hive/jquery-ui-1.8.6.custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/datatables/custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/main/main.css"/>

	<!-- JS Imports -->
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-1.5.2.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-ui-1.8.12.custom.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/datejs/date.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/datatables/jquery.dataTables.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/util/util.js"></script>

	<title>Events</title>
	</head>
	<body class="ui-widget-content">

	<div id="menu">
	<ul>
	<li><a href="${rootUrl}event">Events (DataTables)</a></li>
	<li><a href="${rootUrl}jqgrid/event">Events (jQgrid)</a></li>
	<li><a href="${rootUrl}error">Errors</a></li>
	<li><a href="${rootUrl}monitor/event">Monitor Events</a></li>
	<li><a href="${rootUrl}monitor/error">Monitor Errors</a></li>
	</ul>
	<br style="clear:left"/>
	</div>

	<h3 class="title">Events - DataTables Version</h3>
	<table id='eventTable'>
	<thead>
	<tr>
	<th></th>
	<th>Id</th>
	<th>Name</th>
	<th>Description</th>
	<th>Participants</th>
	<th>Date</th>
	</tr>
	</thead>
	<tbody>
	</tbody>
	</table>

	<c:if test="${empty events}">There are currently no events in the list.</c:if>

	<div class="control">
	<span><a href="#" id="addLink">Add</a></span>
	<span><a href="#" id="editLink">Edit</a></span>
	<span><a href="#" id="deleteLink">Delete</a></span>
	</div>

	<jsp:include page="/WEB-INF/jsp/dialogs/addDialog.jsp"/>
	<jsp:include page="/WEB-INF/jsp/dialogs/editDialog.jsp"/>
	<jsp:include page="/WEB-INF/jsp/dialogs/deleteDialog.jsp"/>
	<jsp:include page="/WEB-INF/jsp/dialogs/genericDialog.jsp"/>

	<script type="text/javascript">
	$(function() {
	// Convert links to buttons
	$('#addLink, #editLink, #deleteLink').button();

	// Assign a function to addLink
	// Displays a dialog form for adding a new record
	$("#addLink").click(function() {
	// Show the dialog
	$( "#addDialog" ).dialog({
	modal: true,
	width: 350,
	close: function(event, ui) { }
	});
	return false;
	});

	// Assign a function to editLink
	// Checks first if a record is selected from the table
	// Then it retrieves that record via jQuery's data()storage method
	// Finally it displays a dialog form for editing the selected record
	$("#editLink").click(function() {
	var tId = $('input:radio[name=eventRadio]:checked').val();
	if (tId == null) {
	$("#genericDialog").text("Select a record first!");
	$("#genericDialog").dialog(
	{ title: 'Error',
	modal: true,
	buttons: {"Ok": function() {
	$(this).dialog("close");}
	}
	});
	} else {
	// Retrieve record
	var record = null;
	for (var i=0; i<$('#eventTable').data('records').length; i++) {
	if ($('#eventTable').data('records')[i].id == tId) {
	record = $('#eventTable').data('records')[i];
	break;
	}
	}

	// Assign record to form fields
	$('#editForm #ename').val(record.name.toString());
	$('#editForm #edate').val(new Date(record.date).toString('yyyy-MM-dd'));
	$('#editForm #edescription').val(record.description.toString());
	$('#editForm #eparticipants').val(record.participants.toString());

	// Show the dialog
	$("#editDialog").dialog({
	modal: true,
	width: 350,
	close: function(event, ui) { }
	});
	}
	return false;
	});

	// Assign a function to deleteLink
	// Checks first if a record is selected from the table
	// Finally it displays a dialog form for deleting the selected record
	$("#deleteLink").click(function() {
	// show dialog box
	var tId = $('input:radio[name=eventRadio]:checked').val();
	if (tId == null) {
	$("#genericDialog").text("Select a record first!");
	$("#genericDialog").dialog(
	{ title: 'Error',
	modal: true,
	buttons: {"Ok": function() {
	$(this).dialog("close");}
	}
	});
	} else {
	$("#deleteDialog").dialog({
	modal: true,
	width: 350,
	close: function(event, ui) { }
	});
	}
	return false;
	});

	// Retrieve all records for the first time
	// Converts table to DataTable as well
	$.getRecords('#eventTable', '${rootUrl}event/getall',
	['id', 'name', 'description', 'participants', 'date'],
	function() {
	$('#eventTable').dataTable( {
	"bJQueryUI": true,
	"sPaginationType": "full_numbers"
	});
	});
	});
	</script>

	</body>
	</html>

view raw event-page.jsp hosted with ❤ by GitHub

Let's discuss each section:

a. URLs
The following section declares two URLs which uses the JSTL core tag: the root and the resources URLs respectively. These URLs are here for reusability purposes:

	<c:url value="/" var="rootUrl"/>
	<c:url value="/resources" var="resourcesUrl"/>

view raw event-page(snippet).jsp hosted with ❤ by GitHub

b. Imports
The following section imports a number of CSS and JavaScript resources which includes the core jQuery library, the DateJS library (a Date utility, http://www.datejs.com/), DataTables (a jQuery plugin, http://datatables.net/), and a custom jQuery plugin for retrieving records via AJAX and inserting records to a table automatically:

	<!-- CSS Imports-->
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/jquery/dark-hive/jquery-ui-1.8.6.custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/datatables/custom.css"/>
	<link rel="stylesheet" type="text/css" media="screen" href="${resourcesUrl}/css/main/main.css"/>

	<!-- JS Imports -->
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-1.5.2.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/jquery/jquery-ui-1.8.12.custom.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/datejs/date.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/datatables/jquery.dataTables.min.js"></script>
	<script type="text/javascript" src="${resourcesUrl}/js/util/util.js"></script>

view raw event-page(snippet).jsp hosted with ❤ by GitHub

c. Menu
The following section declares a menu list:

	<div id="menu">
	<ul>
	<li><a href="${rootUrl}event">Events (DataTables)</a></li>
	<li><a href="${rootUrl}jqgrid/event">Events (jQgrid)</a></li>
	<li><a href="${rootUrl}error">Errors</a></li>
	<li><a href="${rootUrl}monitor/event">Monitor Events</a></li>
	<li><a href="${rootUrl}monitor/error">Monitor Errors</a></li>
	</ul>
	<br style="clear:left"/>
	</div>

view raw event-page(snippet).jsp hosted with ❤ by GitHub

d. Table
The following section creates an empty table and three HTML links (controller links) for adding, editing, and deleting of records. Take note of the table id, eventTable, because this id will be referenced multiple times:

	<h3 class="title">Events - DataTables Version</h3>
	<table id='eventTable'>
	<thead>
	<tr>
	<th></th>
	<th>Id</th>
	<th>Name</th>
	<th>Description</th>
	<th>Participants</th>
	<th>Date</th>
	</tr>
	</thead>
	<tbody>
	</tbody>
	</table>

	<c:if test="${empty events}">There are currently no events in the list.</c:if>

	<div class="control">
	<span><a href="#" id="addLink">Add</a></span>
	<span><a href="#" id="editLink">Edit</a></span>
	<span><a href="#" id="deleteLink">Delete</a></span>
	</div>

view raw event-page(snippet).jsp hosted with ❤ by GitHub

e. Dialogs
The following section includes four external JSPs. The first three JSPs contain form elements for adding, editing, and deleting of records respectively. The fourth dialog is used for displaying generic messages.

	<jsp:include page="/WEB-INF/jsp/dialogs/addDialog.jsp"/>
	<jsp:include page="/WEB-INF/jsp/dialogs/editDialog.jsp"/>
	<jsp:include page="/WEB-INF/jsp/dialogs/deleteDialog.jsp"/>
	<jsp:include page="/WEB-INF/jsp/dialogs/genericDialog.jsp"/>

view raw event-page(snippet).jsp hosted with ❤ by GitHub

f. Conversion of links to buttons
The following section converts the previous three links to a button. This is mainly for aesthetic purposes:

	$(function() {
	// Convert links to buttons
	$('#addLink, #editLink, #deleteLink').button();
	...
	...
	});

view raw event-page(snippet).jsp hosted with ❤ by GitHub

g. Attaching link functions
The following section attaches a function to our controller buttons. Each function will trigger a dialog box. These dialog boxes are the four dialog JSPs we included earlier:

	$(function() {
	...
	...

	// Assign a function to addLink
	// Displays a dialog form for adding a new record
	$("#addLink").click(function() {
	// Show the dialog
	$( "#addDialog" ).dialog({
	modal: true,
	width: 350,
	close: function(event, ui) { }
	});
	return false;
	});

	// Assign a function to editLink
	// Checks first if a record is selected from the table
	// Then it retrieves that record via jQuery's data()storage method
	// Finally it displays a dialog form for editing the selected record
	$("#editLink").click(function() {
	var tId = $('input:radio[name=eventRadio]:checked').val();
	if (tId == null) {
	$("#genericDialog").text("Select a record first!");
	$("#genericDialog").dialog(
	{ title: 'Error',
	modal: true,
	buttons: {"Ok": function() {
	$(this).dialog("close");}
	}
	});
	} else {
	// Retrieve record
	var record = null;
	for (var i=0; i<$('#eventTable').data('records').length; i++) {
	if ($('#eventTable').data('records')[i].id == tId) {
	record = $('#eventTable').data('records')[i];
	break;
	}
	}

	// Assign record to form fields
	$('#editForm #ename').val(record.name.toString());
	$('#editForm #edate').val(new Date(record.date).toString('yyyy-MM-dd'));
	$('#editForm #edescription').val(record.description.toString());
	$('#editForm #eparticipants').val(record.participants.toString());

	// Show the dialog
	$("#editDialog").dialog({
	modal: true,
	width: 350,
	close: function(event, ui) { }
	});
	}
	return false;
	});

	// Assign a function to deleteLink
	// Checks first if a record is selected from the table
	// Finally it displays a dialog form for deleting the selected record
	$("#deleteLink").click(function() {
	// show dialog box
	var tId = $('input:radio[name=eventRadio]:checked').val();
	if (tId == null) {
	$("#genericDialog").text("Select a record first!");
	$("#genericDialog").dialog(
	{ title: 'Error',
	modal: true,
	buttons: {"Ok": function() {
	$(this).dialog("close");}
	}
	});
	} else {
	$("#deleteDialog").dialog({
	modal: true,
	width: 350,
	close: function(event, ui) { }
	});
	}
	return false;
	});

	...
	...
	});

view raw event-page(snippet).jsp hosted with ❤ by GitHub

h. Retrieval of records and conversion to DataTables
The following section calls a custom getRecords() function which will retrieve Event records, populate our table with data, and convert the table to DataTables:

	$(function() {
	...
	...

	// Retrieve all records for the first time
	// Converts table to DataTable as well
	$.getRecords('#eventTable', '${rootUrl}event/getall',
	['id', 'name', 'description', 'participants', 'date'],
	function() {
	$('#eventTable').dataTable( {
	"bJQueryUI": true,
	"sPaginationType": "full_numbers"
	});
	});
	});

view raw event-page(snippet).jsp hosted with ❤ by GitHub

If you want to disable DataTables, just change the previous function to the following:

	$(function() {
	...
	...

	// Retrieve all records for the first time
	// Converts table to DataTable as well
	$.getRecords('#eventTable', '${rootUrl}event/getall',
	['id', 'name', 'description', 'participants', 'date'],
	null);
	});

view raw event-page(snippet).jsp hosted with ❤ by GitHub

Results

When we run the application, the result should be similar to the following image (this is an actual screenshot taken from a live deployment):

Limitations

Our DataTables page has some limitations. However, these are not DataTables limitations but rather something that we intentionally (and unintentionally) did not implement:

The status "Showing 1 to 4 Entries" has a bug when adding or deleting a record. You need to refresh the whole page to show the correct status
Date conversion is in integer format instead of Date
UI validation is not implemented

Playground

Some developers might not have time to build the entire project. Maybe they just want something to play around really fast. Because of that, I've deployed live samples to Cloud Foundry and added sample fiddles via JSFiddle.

JSFiddle

If you want to explore more about DataTables, I've provided fiddles for you to play around. These fiddles do not need any server-side programs to run. Feel free to fork them.

Here are the fiddles:

Plain table with static data: http://jsfiddle.net/krams/Us9S5/
Plain table with dynamic data: http://jsfiddle.net/krams/jD67t/
Add form: http://jsfiddle.net/krams/8QKAe/
Edit form: http://jsfiddle.net/krams/Kf4MF/
Full table with DataTables and buttons: http://jsfiddle.net/krams/9Syqc/

What is JSFiddle?

JsFiddle is a playground for web developers, a tool which may be used in many ways. One can use it as an online editor for snippets build from HTML, CSS and JavaScript. The code can then be shared with others, embedded on a blog, etc. Using this approach, JavaScript developers can very easily isolate bugs. We aim to support all actively developed frameworks - it helps with testing compatibility - Source: http://doc.jsfiddle.net/

Cloud Foundry

If you want to tinker with a live deployment, I suggest you visit the application's live site at http://spring-mysql-mongo-rabbit.cloudfoundry.com/event

What is Cloud Foundry?

Cloud Foundry is the open platform as a service project initiated by VMware. It can support multiple frameworks, multiple cloud providers, and multiple application services all on a cloud scale platform.

Next Section

In the next section, we will explore jQgrid, a jQuery plugin, for displaying tabular data. Read next.

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Top Tabs

Thursday, October 13, 2011

Sunday, October 9, 2011

Review

Table of Contents

Load Balancing

Default Setup

Sharing Sessions

Configure Tomcat to Share Sessions

Retest Session Sharing

Session Sharing Caveat

Next Section

Introduction

Table of Contents

Frequently Asked Questions (FAQ)

An Overview

Requirements

Setting-up the Environment

Download Tomcat

Configure Tomcat

Run Tomcat

Download HAProxy

Configure HAProxy

Run HAProxy

Next Section

Review

Table of Contents

HAProxy Configuration

Configuration File

HAProxy Logging

Overflowing Logs

Rotate Logs

References

Conclusion

Friday, September 16, 2011

Introduction

Table of Contents

Frequently Asked Questions (FAQs)

Required Tools and Services

Screenshots

Live Deployment in the Cloud

Project Structure

Project Dependencies (pom.xml)

Development

A. Event Management

A1. Domain

A2. Service

A3. Controller

A4. View

JMeter Test

A5. Crosscutting Concerns

Next Section

Review

Where am I?

Table of Contents

Error Persistence

C1. Domain

C2. Service

C3. Aspect

C4. Controller

C5. View

Result

Next Section

Review

Where am I?

Table of Contents

Messaging Support

B1. Aspect

B2. Configuration

B3. Controller

B4. View

Result

Next Section

Review

Where am I?

Table of Contents

DataTables

Development

1. Primary page

Results