Spring Data - MongoDB Tutorial (1.0.0.M1)

Introduction

In this tutorial we will refactor an existing Spring MVC 3 - MongoDB application (see here) to use the newly released Spring Data Document 1.0.0.M1 for MongoDB. Our purpose here is to realize how Spring Data simplifies integration development with MongoDB. To appreciate Spring Data, it is advisable to know how to perform basic CRUD functions with native MongoDB support. And that's the reason why we'll be refactoring an existing Spring MVC 3 - MongoDB application.

Note: An updated version of this tutorial is now accessible at Spring MVC 3.1 - Implement CRUD with Spring Data MongoDB (Part 1)

What is MongoDB?

MongoDB (from "humongous") is a scalable, high-performance, open source, document-oriented database. Written in C++, MongoDB features:

• Document-oriented storage
• Full Index Support
• Replication & High Availability
• Scale horizontally without compromising functionality.
• Rich, document-based queries.
• Atomic modifiers for contention-free performance.
• Flexible aggregation and data processing.
• Store files of any size without complicating your stack.
• Enterprise class support, training, and consulting available.

Source: http://www.mongodb.org/

What is Spring Data - Document?

The Spring Data Document (or DATADOC) framework makes it easy to write Spring applications that use a Document store by eliminating the redundant tasks and boiler place code required for interacting with the store through Spring's excellent infrastructure support.

Source: Spring Datastore Document - Reference Documentation

In a nutshell MongoDB uses JSON instead of SQL There's no static schema to create. All schemas are dynamic, meaning you create them on-the-fly. You can try a real-time online shell for MongoDB at http://try.mongodb.org/. Visit the official MongoDB site for a thorough discussion.

Prerequisites
In order to complete this tutorial, you will be required to install a copy of MongoDB. If you don't have one yet, grab a copy now by visiting http://www.mongodb.org/display/DOCS/Quickstart. Installation is really easy.

Development

Our application is a simple CRUD system for managing a list of Persons. Data is stored in MongoDB database. We'll start by declaring our domain objects. Then we'll discuss the service layer. And lastly we'll add the controllers.

The Domain Layer

Our application contains a single domain object named Person. It consists the following properties:

pid
firstName
lastName
money

Here's the class declaration:

Person.java

package org.krams.tutorial.domain;

import java.io.Serializable;

/**
 * A simple POJO representing a Person
 * 
 * @author Krams at {@link http://krams915@blogspot.com}
 */
public class Person implements Serializable {

 private static final long serialVersionUID = -5527566248002296042L;
 
 private String pid;
 private String firstName;
 private String lastName;
 private Double money;

 public String getPid() {
  return pid;
 }

 public void setPid(String pid) {
  this.pid = pid;
 }

 public String getFirstName() {
  return firstName;
 }

 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }

 public String getLastName() {
  return lastName;
 }

 public void setLastName(String lastName) {
  this.lastName = lastName;
 }

 public Double getMoney() {
  return money;
 }

 public void setMoney(Double money) {
  this.money = money;
 }
}

Warning!
In the original tutorial we used id to signify the primary identity of the Person. But in this tutorial we used pid instead. This is because when we use id with Spring Data, it messes up the id property by merging it with the built-in _id property of MongoDB.

For now, if you plan to use Spring Data, don't use id as your id field. Choose a different name instead. I have filed already an inquiry about this behavior in the Spring forums. See it here.

The Service Layer

Our service class contains the main changes in the original application. Instead of calling native MongoDB methods for performing CRUD operations, we use Spring Data's MongoTemplate instead.

What is MongoTemplate?

The template offers convenience methods and automatic mapping between MongoDB JSON documents and your domain classes. Out of the box, MongoTemplate uses a Java-based default converter but you can also write your own converter classes to be used for reading and storing domain objects.

Source: Spring Datastore Document - Reference Documentation

Here's the class declaration:

PersonService.java

package org.krams.tutorial.service;

import java.util.List;
import java.util.UUID;

import javax.annotation.Resource;
import org.apache.log4j.Logger;
import org.krams.tutorial.domain.Person;
import org.springframework.data.document.mongodb.MongoTemplate;
import org.springframework.data.document.mongodb.query.Query;
import org.springframework.data.document.mongodb.query.Update;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import static org.springframework.data.document.mongodb.query.Criteria.where;

/**
 * Service for processing {@link Person} objects.
 * Uses Spring's {@link MongoTemplate} to perform CRUD operations.
 * <p>
 * For a complete reference to MongoDB
 * see http://www.mongodb.org/
 * <p>
 * For a complete reference to Spring Data MongoDB 
 * see http://www.springsource.org/spring-data
 * 
 * @author Krams at {@link http://krams915@blogspot.com}
 */
@Service("personService")
@Transactional
public class PersonService {

 protected static Logger logger = Logger.getLogger("service");
 
 @Resource(name="mongoTemplate")
 private MongoTemplate mongoTemplate;
 
 /**
  * Retrieves all persons
  */
 public List<Person> getAll() {
  logger.debug("Retrieving all persons");
 
  // Find an entry where pid property exists
        Query query = new Query(where("pid").exists(true));
        // Execute the query and find all matching entries
        List<Person> persons = mongoTemplate.find(query, Person.class);
        
  return persons;
 }
 
 /**
  * Retrieves a single person
  */
 public Person get( String id ) {
  logger.debug("Retrieving an existing person");
  
  // Find an entry where pid matches the id
        Query query = new Query(where("pid").is(id));
        // Execute the query and find one matching entry
        Person person = mongoTemplate.findOne("mycollection", query, Person.class);
     
  return person;
 }
 
 /**
  * Adds a new person
  */
 public Boolean add(Person person) {
  logger.debug("Adding a new user");
  
  try {
   
   // Set a new value to the pid property first since it's blank
   person.setPid(UUID.randomUUID().toString());
   // Insert to db
      mongoTemplate.insert("mycollection", person);

   return true;
   
  } catch (Exception e) {
   logger.error("An error has occurred while trying to add new user", e);
   return false;
  }
 }
 
 /**
  * Deletes an existing person
  */
 public Boolean delete(String id) {
  logger.debug("Deleting existing person");
  
  try {
   
   // Find an entry where pid matches the id
         Query query = new Query(where("pid").is(id));
         // Run the query and delete the entry
         mongoTemplate.remove(query);
         
   return true;
   
  } catch (Exception e) {
   logger.error("An error has occurred while trying to delete new user", e);
   return false;
  }
 }
 
 /**
  * Edits an existing person
  */
 public Boolean edit(Person person) {
  logger.debug("Editing existing person");
  
  try {
   
   // Find an entry where pid matches the id
         Query query = new Query(where("pid").is(person.getPid()));
         
   // Declare an Update object. 
         // This matches the update modifiers available in MongoDB
   Update update = new Update();
         
         update.set("firstName", person.getFirstName());
         mongoTemplate.updateMulti(query, update);
         
         update.set("lastName", person.getLastName());
         mongoTemplate.updateMulti(query, update);
         
         update.set("money", person.getMoney());
         mongoTemplate.updateMulti(query, update);
         
   return true;
   
  } catch (Exception e) {
   logger.error("An error has occurred while trying to edit existing user", e);
   return false;
  }
  
 }
}

The code should should be self-explanatory. Notice how Spring Data has reduced the amount of code. To appreciate this difference, let's do a comparison between using the traditional MongoDB and using Spring Data.

Retrieving all entries

old implementation

public List<person> getAll() {
  logger.debug("Retrieving all persons");
   
  // Retrieve collection
  DBCollection coll = MongoDBFactory.getCollection("mydb","mycollection");
  // Retrieve cursor for iterating records
     DBCursor cur = coll.find();
     // Create new list
  List<person> items = new ArrayList<person>();
  // Iterate cursor
        while(cur.hasNext()) {
         // Map DBOject to Person
         DBObject dbObject = cur.next();
         Person person = new Person();
          
         person.setId(dbObject.get("id").toString());
         person.setFirstName(dbObject.get("firstName").toString());
         person.setLastName(dbObject.get("lastName").toString());
         person.setMoney(Double.valueOf(dbObject.get("money").toString()));
 
         // Add to new list
         items.add(person);
        }
         
        // Return list
  return items;
 }

new implementation

public List<Person> getAll() {
  logger.debug("Retrieving all persons");
 
        Query query = new Query(where("pid").exists(true));
        List<Person> persons = mongoTemplate.find(query, Person.class);
        
  return persons;
 }

Retrieving a single entry

old implementation

public Person get( String id ) {
  logger.debug("Retrieving an existing person");
   
  // Retrieve collection
  DBCollection coll = MongoDBFactory.getCollection("mydb","mycollection");
  // Create a new object
  DBObject doc = new BasicDBObject();
  // Put id to search
        doc.put("id", id);
         
        // Find and return the person with the given id
        DBObject dbObject = coll.findOne(doc);
         
        // Map DBOject to Person
     Person person = new Person();
     person.setId(dbObject.get("id").toString());
     person.setFirstName(dbObject.get("firstName").toString());
     person.setLastName(dbObject.get("lastName").toString());
     person.setMoney(Double.valueOf(dbObject.get("money").toString()));
      
        // Return person
  return person;
 }

new implementation

public Person get( String id ) {
  logger.debug("Retrieving an existing person");
  
  // Find an entry where pid matches the id
        Query query = new Query(where("pid").is(id));
        // Execute the query and find one matching entry
        Person person = mongoTemplate.findOne("mycollection", query, Person.class);
     
  return person;
 }

Adding a new entry

old implementation

public Boolean add(Person person) {
  logger.debug("Adding a new user");
   
  try {
   // Retrieve collection
   DBCollection coll = MongoDBFactory.getCollection("mydb","mycollection");
   // Create a new object
   BasicDBObject doc = new BasicDBObject();
   // Generate random id using UUID type 4
   // See http://en.wikipedia.org/wiki/Universally_unique_identifier
         doc.put("id", UUID.randomUUID().toString() ); 
         doc.put("firstName", person.getFirstName());
         doc.put("lastName", person.getLastName());
         doc.put("money", person.getMoney());
         // Save new person
         coll.insert(doc);
          
   return true;
    
  } catch (Exception e) {
   logger.error("An error has occurred while trying to add new user", e);
   return false;
  }
 }

new implementation

public Boolean add(Person person) {
  logger.debug("Adding a new user");
  
  try {
   
   // Set a new value to the pid property first since it's blank
   person.setPid(UUID.randomUUID().toString());
   // Insert to db
      mongoTemplate.insert("mycollection", person);

   return true;
   
  } catch (Exception e) {
   logger.error("An error has occurred while trying to add new user", e);
   return false;
  }
 }

Deleting an entry

old implementation

public Boolean delete(String id) {
  logger.debug("Deleting existing person");
   
  try {
   // Retrieve person to delete
   BasicDBObject item = (BasicDBObject) getDBObject( id );
   // Retrieve collection
   DBCollection coll = MongoDBFactory.getCollection("mydb","mycollection");
   // Delete retrieved person
         coll.remove(item);
          
   return true;
    
  } catch (Exception e) {
   logger.error("An error has occurred while trying to delete new user", e);
   return false;
  }
 }

new implementation

public Boolean delete(String id) {
  logger.debug("Deleting existing person");
  
  try {
   
   // Find an entry where pid matches the id
         Query query = new Query(where("pid").is(id));
         // Run the query and delete the entry
         mongoTemplate.remove(query);
         
   return true;
   
  } catch (Exception e) {
   logger.error("An error has occurred while trying to delete new user", e);
   return false;
  }
 }

Updating an entry

old implementation

public Boolean edit(Person person) {
  logger.debug("Editing existing person");
   
  try {
   // Retrieve person to edit
   BasicDBObject existing = (BasicDBObject) getDBObject( person.getId() );
    
   DBCollection coll = MongoDBFactory.getCollection("mydb","mycollection");
    
   // Create new object
   BasicDBObject edited = new BasicDBObject();
   // Assign existing details
   edited.put("id", person.getId()); 
   edited.put("firstName", person.getFirstName());
   edited.put("lastName", person.getLastName());
   edited.put("money", person.getMoney());
   // Update existing person
         coll.update(existing, edited);
          
   return true;
    
  } catch (Exception e) {
   logger.error("An error has occurred while trying to edit existing user", e);
   return false;
  }
   
 }

new implementation

public Boolean edit(Person person) {
  logger.debug("Editing existing person");
  
  try {
   
   // Find an entry where pid matches the id
         Query query = new Query(where("pid").is(person.getPid()));
         
   // Declare an Update object. 
         // This matches the update modifiers available in MongoDB
   Update update = new Update();
         
         update.set("firstName", person.getFirstName());
         mongoTemplate.updateMulti(query, update);
         
         update.set("lastName", person.getLastName());
         mongoTemplate.updateMulti(query, update);
         
         update.set("money", person.getMoney());
         mongoTemplate.updateMulti(query, update);
         
   return true;
   
  } catch (Exception e) {
   logger.error("An error has occurred while trying to edit existing user", e);
   return false;
  }
  
 }

Configuration

To use Spring's MongoTemplate it needs to be declared via configuration. It also needs a reference to a MongoDB database. Let's declare an XML configuration that satifies these requirements:

mongo-config.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:mongo="http://www.springframework.org/schema/data/mongo"
 xsi:schemaLocation="http://www.springframework.org/schema/beans 
      http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
      http://www.springframework.org/schema/data/mongo
      http://www.springframework.org/schema/data/mongo/spring-mongo-1.0.xsd">
 
 <!-- Default bean name is 'mongo' -->
 <mongo:mongo host="localhost" port="27017"/>
 
 <!-- Offers convenience methods and automatic mapping between MongoDB JSON documents and your domain classes. -->
   <bean id="mongoTemplate" class="org.springframework.data.document.mongodb.MongoTemplate">
     <constructor-arg ref="mongo"/>
     <constructor-arg value="mydb"/>
     <constructor-arg value="mycollection"/>
   </bean>
   
   <bean id="initService" class="org.krams.tutorial.service.InitService" init-method="init"></bean>
</beans>

Notice we're using the mongo namespace:

xmlns:mongo="http://www.springframework.org/schema/data/mongo"

We've declared a reference to a MongoDB database by declaring:

<mongo:mongo host="localhost" port="27017"/>

Then we declared a MongoTemplate that references a MongoDB database (mongo), a database (mydb), and a collection (mycollection):

<bean id="mongoTemplate" class="org.springframework.data.document.mongodb.MongoTemplate">
     <constructor-arg ref="mongo"/>
     <constructor-arg value="mydb"/>
     <constructor-arg value="mycollection"/>
   </bean>

Lastly, we declared an initService

<bean id="initService" class="org.krams.tutorial.service.InitService" init-method="init"></bean>

The purpose of the initService is to prepopulate our MongoDB with sample data.

Here's the class declaration:

InitService.java

package org.krams.tutorial.service;

import java.util.UUID;

import javax.annotation.Resource;
import org.apache.log4j.Logger;
import org.krams.tutorial.domain.Person;
import org.springframework.data.document.mongodb.MongoTemplate;
import org.springframework.transaction.annotation.Transactional;

/**
 * Service for initializing MongoDB with sample data
 * <p>
 * For a complete reference to MongoDB
 * see http://www.mongodb.org/
 * <p>
 * For transactions, see http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/transaction.html
 * 
 * @author Krams at {@link http://krams915@blogspot.com}
 */
@Transactional
public class InitService {

 protected static Logger logger = Logger.getLogger("service");
 
 @Resource(name="mongoTemplate")
 private MongoTemplate mongoTemplate;

 private void init() {
  // Populate our MongoDB database
  logger.debug("Init MongoDB users");
  
  // Drop existing collection
  mongoTemplate.dropCollection("mycollection");
  
  // Create new object
  Person p = new Person ();
  p.setPid(UUID.randomUUID().toString());
  p.setFirstName("John");
  p.setLastName("Smith");
  p.setMoney(1000.0);
  
  // Insert to db
     mongoTemplate.insert("mycollection", p);

     // Create new object
  p = new Person ();
  p.setPid(UUID.randomUUID().toString());
  p.setFirstName("Jane");
  p.setLastName("Adams");
  p.setMoney(2000.0);
  
  // Insert to db
     mongoTemplate.insert("mycollection", p);
        
     // Create new object
  p = new Person ();
  p.setPid(UUID.randomUUID().toString());
  p.setFirstName("Jeff");
  p.setLastName("Mayer");
  p.setMoney(3000.0);
  
  // Insert to db
     mongoTemplate.insert("mycollection", p);
 }
}

The Controller Layer

After creating the domain and service classes, we need to declare a controller that will handle the web requests.

MainController.java

package org.krams.tutorial.controller;

import java.util.List;
import javax.annotation.Resource;
import org.apache.log4j.Logger;
import org.krams.tutorial.domain.Person;
import org.krams.tutorial.service.PersonService;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;


/**
 * Handles and retrieves person request
 * 
 * @author Krams at {@link http://krams915@blogspot.com}
 */
@Controller
@RequestMapping("/main")
public class MainController {

 protected static Logger logger = Logger.getLogger("controller");
 
 @Resource(name="personService")
 private PersonService personService;
 
 /**
  * Handles and retrieves all persons and show it in a JSP page
  * 
  * @return the name of the JSP page
  */
    @RequestMapping(value = "/persons", method = RequestMethod.GET)
    public String getPersons(Model model) {
     
     logger.debug("Received request to show all persons");
     
     // Retrieve all persons by delegating the call to PersonService
     List persons = personService.getAll();
     
     // Attach persons to the Model
     model.addAttribute("persons", persons);
     
     // This will resolve to /WEB-INF/jsp/personspage.jsp
     return "personspage";
 }
    
    /**
     * Retrieves the add page
     * 
     * @return the name of the JSP page
     */
    @RequestMapping(value = "/persons/add", method = RequestMethod.GET)
    public String getAdd(Model model) {
     logger.debug("Received request to show add page");
    
     // Create new Person and add to model
     // This is the formBackingOBject
     model.addAttribute("personAttribute", new Person());

     // This will resolve to /WEB-INF/jsp/addpage.jsp
     return "addpage";
 }
 
    /**
     * Adds a new person by delegating the processing to PersonService.
     * Displays a confirmation JSP page
     * 
     * @return  the name of the JSP page
     */
    @RequestMapping(value = "/persons/add", method = RequestMethod.POST)
    public String add(@ModelAttribute("personAttribute") Person person) {
  logger.debug("Received request to add new person");
  
     // The "personAttribute" model has been passed to the controller from the JSP
     // We use the name "personAttribute" because the JSP uses that name
  
  // Call PersonService to do the actual adding
  personService.add(person);

     // This will resolve to /WEB-INF/jsp/addedpage.jsp
  return "addedpage";
 }
    
    /**
     * Deletes an existing person by delegating the processing to PersonService.
     * Displays a confirmation JSP page
     * 
     * @return  the name of the JSP page
     */
    @RequestMapping(value = "/persons/delete", method = RequestMethod.GET)
    public String delete(@RequestParam(value="pid", required=true) String id, 
              Model model) {
   
  logger.debug("Received request to delete existing person");
  
  // Call PersonService to do the actual deleting
  personService.delete(id);
  
  // Add id reference to Model
  model.addAttribute("pid", id);
     
     // This will resolve to /WEB-INF/jsp/deletedpage.jsp
  return "deletedpage";
 }
    
    /**
     * Retrieves the edit page
     * 
     * @return the name of the JSP page
     */
    @RequestMapping(value = "/persons/edit", method = RequestMethod.GET)
    public String getEdit(@RequestParam(value="pid", required=true) String id,  
              Model model) {
     logger.debug("Received request to show edit page");
    
     // Retrieve existing Person and add to model
     // This is the formBackingOBject
     model.addAttribute("personAttribute", personService.get(id));
     
     // This will resolve to /WEB-INF/jsp/editpage.jsp
     return "editpage";
 }
    
    /**
     * Edits an existing person by delegating the processing to PersonService.
     * Displays a confirmation JSP page
     * 
     * @return  the name of the JSP page
     */
    @RequestMapping(value = "/persons/edit", method = RequestMethod.POST)
    public String saveEdit(@ModelAttribute("personAttribute") Person person, 
                 @RequestParam(value="pid", required=true) String id, 
                Model model) {
     logger.debug("Received request to update person");
    
     // The "personAttribute" model has been passed to the controller from the JSP
     // We use the name "personAttribute" because the JSP uses that name
     
     // We manually assign the id because we disabled it in the JSP page
     // When a field is disabled it will not be included in the ModelAttribute
     person.setPid(id);
     
     // Delegate to PersonService for editing
     personService.edit(person);
     
     // Add id reference to Model
  model.addAttribute("pid", id);
  
     // This will resolve to /WEB-INF/jsp/editedpage.jsp
  return "editedpage";
 }
    
}

Our controller is a simple class that delegates actual processing to PersonService. When the service is done processing, the controller forwards the result to a JSP view.

Other Configurations and Files

To make the tutorial manageable, I've decided not to post the following configuration files in this tutorial:

web.xml
spring-servlet.xml
applicationContext.xml

These files are standard Spring MVC related configuration files. You can find them in the downloadable application at the end of this tutorial.

I have also left out the JSP declarations. You can find a description of them in the following tutorial: Spring MVC 3: Using a Document-Oriented Database - MongoDB

Run the Application

To run the application, open your browser and enter the following URL:

http://localhost:8080/spring-data-mongodb/krams/main/persons

You should see the following CRUD view:

Conclusion

That's it. We have successfully refactored our existing Spring MVC 3 - MongoDB application to use the newly released Spring Data Document 1.0 for MongoDB. We've compared side-by-side between the native MongoDB development and with the new Spring Data framework. We have seen how Spring Data has simplified our development further.

Download the project
You can access the project site at Google's Project Hosting at http://code.google.com/p/spring-mvc-mongodb/

You can download the project as a Maven build. Look for the spring-data-mongodb.zip in the Download sections.

You can run the project directly using an embedded server via Maven.
For Tomcat: mvn tomcat:run
For Jetty: mvn jetty:run

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

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