Showing posts with label ORM. Show all posts

Friday, March 18, 2011

Spring - Hibernate: One-To-Many Association

Introduction

In this tutorial we'll explore how to implement a one-to-many association using Hibernate Annotations and Spring MVC 3. We will use @OneToMany annotation to specify the relationship between our objects. We will not specify Cascade types or Fetch strategies, but instead rely on @OneToMany's default settings.

If you want to see how to implement this project using @ManyToOne annotation instead, see Spring - Hibernate: Many-To-One Association.

Spring MVC 3 and Hibernate Tutorials Series
Spring - Hibernate: Many-To-One Association - Explicitly Specify Join Table, Cascade, and Fetch
Spring - Hibernate: One-To-Many Association - Explicitly Specify Join Table, Cascade, and Fetch
Spring - Hibernate: Many-To-One Association
Spring - Hibernate: One-To-Many Association
Spring MVC 3, Hibernate Annotations, MySQL Integration Tutorial
Spring MVC 3, Hibernate Annotations, HSQLDB Integration Tutorial

What is One-To-Many Association?

One-to-many relationships occur when each record in TableA may have many linked records in TableB but each record in TableB may have only one corresponding record in TableA.

Source: http://databases.about.com/od/specificproducts/g/onetomany.htm

Specification

Our application is simple CRUD system for managing a list of records. Each record corresponds to a single person containing personal information and credit card details. Each person can own zero or more credit cards. Moreover, a person's person information is edited separately from his credit card details.

Below are sample screenshots from the application:

Domain Objects

Based on the specs, we have two domain objects: Person and Credit Card.

A Person object has the following properties:

id
first name
last name
money
credit cards

Whereas a Credit Card object has the following properties:

id
type
number

Notice each Person can have multiple Credit Cards hence, the one-to-many relationship. We can of course look at this relationship the other way around: many-to-one relationship. But that topic is for another tutorial.

Development

We'll split our development in three layers: Domain, Service, and Controller. Then we'll declare the configuration files. Let's start with the Domain layer.

Domain Layer

As discussed earlier, we have two domain objects: Person and Credit Card. Consequently, we'll declare two POJOs to represent our domain. Each POJO will be annotated with @Entity so that we can persist them to a database.

Person.java

package org.krams.tutorial.domain;

import java.io.Serializable;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

/**
 * Represents a person entity
 * 
 *  @author Krams at {@link http://krams915@blogspot.com}
 */
@Entity
@Table(name = "PERSON")
public class Person implements Serializable {

 private static final long serialVersionUID = -5527566248002296042L;
 
 @Id
 @Column(name = "ID")
 @GeneratedValue
 private Integer id;
 
 @Column(name = "FIRST_NAME")
 private String firstName;
 
 @Column(name = "LAST_NAME")
 private String lastName;
 
 @Column(name = "MONEY")
 private Double money;

 @OneToMany
 private Set<CreditCard> creditCards;
 
 public Integer getId() {
  return id;
 }

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

 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;
 }

 public Set<CreditCard> getCreditCards() {
  return creditCards;
 }

 public void setCreditCards(Set<CreditCard> creditCards) {
  this.creditCards = creditCards;
 }
}

Person object has been mapped to the PERSON table. The table that gets auto-generated looks as follows:

Notice the @OneToMany annotation for the field creditCards. We did not specify any Cascade type or Fetch strategy for this field. Instead, we rely on the annotation's default settings. Later we'll discover some issues for not specifying them.

@Entity
@Table(name = "PERSON")
public class Person implements Serializable {

 ...

 @OneToMany
 private Set<CreditCard> creditCards;
 
 ...
}

CreditCard.java

package org.krams.tutorial.domain;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * Represents a credit card entity
 * 
 *  @author Krams at {@link http://krams915@blogspot.com}
 */
@Entity
@Table(name = "CREDIT_CARD")
public class CreditCard implements Serializable {

 private static final long serialVersionUID = 5924361831551833717L;

 @Id
 @Column(name = "ID")
 @GeneratedValue
 private Integer id;
 
 @Column(name = "TYPE")
 private String type;
 
 @Column(name = "NUMBER")
 private String number;

 public Integer getId() {
  return id;
 }

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

 public String getType() {
  return type;
 }

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

 public String getNumber() {
  return number;
 }

 public void setNumber(String number) {
  this.number = number;
 }
}

CreditCard object has been mapped to the CREDIT_CARD table. The table that gets auto-generated looks as follows:

Using phpymyadmin's database designer, the Hibernate auto-generated relationship between Person and CreditCard looks as follows:

Again using phpymyadmin, the auto-generated tables looks as follows:

We only declared two entities: a Person entity and a CreditCard entity. We expect two tables in the database; however, we have three tables in the database instead. Why? The default behavior of @OneToMany is it will create a third table acting as the join table.

Here's a quote from the Hibernate Annotations Reference guide:

Without describing any physical mapping, a unidirectional one to many with join table is used. The table name is the concatenation of the owner table name, _, and the other side table name. The foreign key name(s) referencing the owner table is the concatenation of the owner table, _, and the owner primary key column(s) name. The foreign key name(s) referencing the other side is the concatenation of the owner property name, _, and the other side primary key column(s) name. A unique constraint is added to the foreign key referencing the other side table to reflect the one to many.

The Hibernate Annotations Reference is stating the behavior in terms of the database structure. Later we'll discuss some issues when relying on the default settings, especially in the Service layer.

Service Layer

After declaring the Domain objects, we'll now proceed with the Service layer which contains two services: a PersonService and a CreditCardService.

PersonService
PersonService is responsible for handling CRUD operations for Person entities. Each method is eventually delegated to a Hibernate Session object.

PersonService.java

package org.krams.tutorial.service;

import java.util.List;
import java.util.Set;

import javax.annotation.Resource;

import org.apache.log4j.Logger;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.krams.tutorial.domain.CreditCard;
import org.krams.tutorial.domain.Person;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

/**
 * Service for processing Persons
 * 
 * @author Krams at {@link http://krams915@blogspot.com
 */
@Service("personService")
@Transactional
public class PersonService {

 protected static Logger logger = Logger.getLogger("service");
 
 @Resource(name="sessionFactory")
 private SessionFactory sessionFactory;
 
 /**
  * Retrieves all persons
  * 
  * @return a list of persons
  */
 public List<Person> getAll() {
  logger.debug("Retrieving all persons");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();

  // Create a Hibernate query (HQL)
  Query query = session.createQuery("FROM Person");
  
  // Retrieve all
  return  query.list();
 }
 
 /**
  * Retrieves a single person
  */
 public Person get( Integer id ) {
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Retrieve existing person
  // Create a Hibernate query (HQL)
  Query query = session.createQuery("FROM Person as p LEFT JOIN FETCH  p.creditCards WHERE p.id="+id);
  
  return (Person) query.uniqueResult();
 }
 
 /**
  * Adds a new person
  */
 public void add(Person person) {
  logger.debug("Adding new person");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Persists to db
  session.save(person);
 }
 
 /**
  * Deletes an existing person
  * @param id the id of the existing person
  */
 public void delete(Integer id) {
  logger.debug("Deleting existing person");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Create a Hibernate query (HQL)
  Query query = session.createQuery("FROM Person as p LEFT JOIN FETCH  p.creditCards WHERE p.id="+id);
 
  // Retrieve record
  Person person = (Person) query.uniqueResult();
  
  Set<CreditCard> creditCards =person.getCreditCards();
  
  // Delete person
  session.delete(person);
  
  // Delete associated credit cards
  for (CreditCard creditCard: creditCards) {
   session.delete(creditCard);
  }
 }
 
 /**
  * Edits an existing person
  */
 public void edit(Person person) {
  logger.debug("Editing existing person");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Retrieve existing person via id
  Person existingPerson = (Person) session.get(Person.class, person.getId());
  
  // Assign updated values to this person
  existingPerson.setFirstName(person.getFirstName());
  existingPerson.setLastName(person.getLastName());
  existingPerson.setMoney(person.getMoney());

  // Save updates
  session.save(existingPerson);
 }
}

PersonService deceptively looks simple; however it solves two main issues that deserves special attention:

Issue #1: Fetch Strategy
Retrieving a Person record (owner) doesn't load its associated CreditCard records (owned entities).

The following query retrieves a Person based on its id.

Query query = session.createQuery("FROM Person WHERE p.id="+id);

The problem with the previous query is it doesn't load the associated CreditCards. This is because we did not specify a Fetch strategy when we declared the @OneToMany annotation. To fix that we use the following query instead:

Query query = session.createQuery("FROM Person as p LEFT JOIN FETCH  p.creditCards WHERE p.id="+id);

Issue #2: Cascade Type
Deleting a Person record doesn't delete its associated CreditCard records.

The following query deletes a Person record:

session.delete(person);

The problem with the previous query is it doesn't delete the associated CreditCards. This is because we did not specify a Cascade type when we declared the @OneToMany annotation. That means we have to implement our own strategy for deleting the CreditCard records.

To resolve the issue we first make a FETCH query. Retrieve the CreditCard objects and assigned them to a temporary object. We then delete the Person record. Afterwards, we loop each credit card record, and delete them one by one.

// Create a Hibernate query (HQL)
  Query query = session.createQuery("FROM Person as p LEFT JOIN FETCH  p.creditCards WHERE p.id="+id);
 
  // Retrieve record
  Person person = (Person) query.uniqueResult();
  
  Set<CreditCard> creditCards =person.getCreditCards();
  
  // Delete person
  session.delete(person);
  
  // Delete associated credit cards
  for (CreditCard creditCard: creditCards) {
   session.delete(creditCard);
  }

CreditCardService
CreditCardService is responsible for handling CRUD operations for CreditCard entities. Each method is eventually delegated to a Hibernate Session object.

CreditCardService.java

package org.krams.tutorial.service;

import java.util.ArrayList;
import java.util.List;
import javax.annotation.Resource;

import org.apache.log4j.Logger;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.krams.tutorial.domain.CreditCard;
import org.krams.tutorial.domain.Person;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

/**
 * Service for processing Credit Cards
 * 
 * @author Krams at {@link http://krams915@blogspot.com
 */
@Service("creditCardService")
@Transactional
public class CreditCardService {

 protected static Logger logger = Logger.getLogger("service");
 
 @Resource(name="sessionFactory")
 private SessionFactory sessionFactory;
 
 /**
  * Retrieves all credit cards
  */
 public List<CreditCard> getAll(Integer personId) {
  logger.debug("Retrieving all credit cards");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Create a Hibernate query (HQL)
  Query query = session.createQuery("FROM Person as p LEFT JOIN FETCH  p.creditCards WHERE p.id="+personId);
  
  Person person = (Person) query.uniqueResult();
  
  // Retrieve all
  return  new ArrayList<CreditCard>(person.getCreditCards());
 }
 
 /**
  * Retrieves all credit cards
  */
 public List<CreditCard> getAll() {
  logger.debug("Retrieving all credit cards");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Create a Hibernate query (HQL)
  Query query = session.createQuery("FROM  CreditCard");
  
  // Retrieve all
  return  query.list();
 }
 
 /**
  * Retrieves a single credit card
  */
 public CreditCard get( Integer id ) {
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Retrieve existing credit card
  CreditCard creditCard = (CreditCard) session.get(CreditCard.class, id);
  
  // Persists to db
  return creditCard;
 }
 
 /**
  * Adds a new credit card
  */
 public void add(Integer personId, CreditCard creditCard) {
  logger.debug("Adding new credit card");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
 
  // Persists to db
  session.save(creditCard);
  
  // Add to person as well
  // Retrieve existing person via id
  Person existingPerson = (Person) session.get(Person.class, personId);
  
  // Assign updated values to this person
  existingPerson.getCreditCards().add(creditCard);

  // Save updates
  session.save(existingPerson);
 }
 
 /**
  * Deletes an existing credit card
  */
 public void delete(Integer id) {
  logger.debug("Deleting existing credit card");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
     // Delete reference to foreign key credit card first
  // We need a SQL query instead of HQL query here to access the third table
     Query query = session.createSQLQuery("DELETE FROM PERSON_CREDIT_CARD " +
       "WHERE creditCards_ID="+id);
     
     query.executeUpdate();
     
  // Retrieve existing credit card
  CreditCard creditCard = (CreditCard) session.get(CreditCard.class, id);
  
  // Delete 
  session.delete(creditCard);
 }
 
 /**
  * Edits an existing credit card
  */
 public void edit(CreditCard creditCard) {
  logger.debug("Editing existing creditCard");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Retrieve existing credit card via id
  CreditCard existingCreditCard = (CreditCard) session.get(CreditCard.class, creditCard.getId());
  
  // Assign updated values to this credit card
  existingCreditCard.setNumber(creditCard.getNumber());
  existingCreditCard.setType(creditCard.getType());

  // Save updates
  session.save(existingCreditCard);
 }
}

CreditCardService's delete() method deserves extra attention:

public void delete(Integer id) {
  logger.debug("Deleting existing credit card");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
     // Delete reference to foreign key credit card first
  // We need a SQL query instead of HQL query here to access the third table
     Query query = session.createSQLQuery("DELETE FROM PERSON_CREDIT_CARD " +
       "WHERE creditCards_ID="+id);
     
     query.executeUpdate();
     
  // Retrieve existing credit card
  CreditCard creditCard = (CreditCard) session.get(CreditCard.class, id);
  
  // Delete 
  session.delete(creditCard);
 }

To delete a CreditCard entity, we have to delete it first from the PERSON_CREDIT_CARD table using the following SQL query:

Query query = session.createSQLQuery("DELETE FROM PERSON_CREDIT_CARD " +
"WHERE creditCards_ID="+id);

Notice PERSON_CREDIT_CARD is the join table created by Hibernate and the query is a SQL not HQL.

After running the SQL statement, we delete the CreditCard entity from the CREDIT_CARD table using

session.delete(creditCard)

.

Why do we need to undergo such process? Can't we just run session.delete(creditCard) directly? We can't because there's a foreign key constraint under PERSON_CREDIT_CARD join table.

Controller Layer

After declaring the Domain and Service objects, we'll now proceed with the Controller layer.
We'll declare two controllers: MainController and CreditCardController.

MainController
MainController is responsible for handling request for Person records. Each CRUD request is ultimately delegated to the PersonService and then returns an appropriate JSP page.

MainController.java

package org.krams.tutorial.controller;

import java.util.ArrayList;
import java.util.List;

import javax.annotation.Resource;

import org.apache.log4j.Logger;
import org.krams.tutorial.domain.Person;
import org.krams.tutorial.dto.PersonDTO;
import org.krams.tutorial.service.CreditCardService;
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 person request
 * 
 * @author Krams at {@link http://krams915@blogspot.com
 */
@Controller
@RequestMapping("/main/record")
public class MainController {

 protected static Logger logger = Logger.getLogger("controller");
 
 @Resource(name="personService")
 private PersonService personService;
 
 @Resource(name="creditCardService")
 private CreditCardService creditCardService;
 
 /**
  * Retrieves the "Records" page
  */
    @RequestMapping(value = "/list", method = RequestMethod.GET)
    public String getRecords(Model model) {
     logger.debug("Received request to show records page");
     
     // Retrieve all persons
     List<Person> persons = personService.getAll();
     
     // Prepare model object
     List<PersonDTO> personsDTO = new ArrayList<PersonDTO>();
     
     for (Person person: persons) {
      // Create new data transfer object
      PersonDTO dto = new PersonDTO();
      
   dto.setId(person.getId());
   dto.setFirstName(person.getFirstName());
   dto.setLastName(person.getLastName());
   dto.setMoney(person.getMoney());
   dto.setCreditCards(creditCardService.getAll(person.getId()));
   
   // Add to model list
   personsDTO.add(dto);
     }
     
     // Add to model
     model.addAttribute("persons", personsDTO);

     // This will resolve to /WEB-INF/jsp/records.jsp
  return "records";
 }
    
    /**
     *  Retrieves the "Add New Record" page
     */
    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public String getAdd(Model model) {
     logger.debug("Received request to show add page");
    
     // Create new Person and add to model
     model.addAttribute("personAttribute", new Person());

     // This will resolve to /WEB-INF/jsp/add-record.jsp
     return "add-record";
 }
 
    /**
     * Adds a new record
     */
    @RequestMapping(value = "/add", method = RequestMethod.POST)
    public String postAdd(@ModelAttribute("personAttribute") Person person) {
  logger.debug("Received request to add new record");

  // Delegate to service
  personService.add(person);

  // Redirect to url
  return "redirect:/krams/main/record/list";
 }
    
    /**
     * Deletes a record including all the associated credit cards
     */
    @RequestMapping(value = "/delete", method = RequestMethod.GET)
    public String getDelete(@RequestParam("id") Integer personId) {
     logger.debug("Received request to delete record");
     
     // Delete person
  personService.delete(personId);

  // Redirect to url
  return "redirect:/krams/main/record/list";
 }
    
    /**
     * Retrieves the "Edit Existing Record" page
     */
    @RequestMapping(value = "/edit", method = RequestMethod.GET)
    public String getEdit(@RequestParam("id") Integer personId, Model model) {
     logger.debug("Received request to show edit page");
     
     // Retrieve person by id
     Person existingPerson = personService.get(personId);

     // Add to model
     model.addAttribute("personAttribute", existingPerson);

     // This will resolve to /WEB-INF/jsp/edit-record.jsp
     return "edit-record";
 }
 
    /**
     * Edits an existing record
     */
    @RequestMapping(value = "/edit", method = RequestMethod.POST)
    public String postEdit(@RequestParam("id") Integer personId, 
              @ModelAttribute("personAttribute") Person person) {
  logger.debug("Received request to edit existing person");
  
  // Assign id
  person.setId(personId);
  
  // Delegate to service
  personService.edit(person);

  // Redirect to url
  return "redirect:/krams/main/record/list";
 }
    
}

Notice the getRecords() method maps the Person and CreditCard records to a data transfer object: PersonDTO

/**
  * Retrieves the "Records" page
  */
    @RequestMapping(value = "/list", method = RequestMethod.GET)
    public String getRecords(Model model) {
     logger.debug("Received request to show records page");
     
     // Retrieve all persons
     List<Person> persons = personService.getAll();
     
     // Prepare model object
     List<PersonDTO> personsDTO = new ArrayList<PersonDTO>();
     
     for (Person person: persons) {
      // Create new data transfer object
      PersonDTO dto = new PersonDTO();
      
   dto.setId(person.getId());
   dto.setFirstName(person.getFirstName());
   dto.setLastName(person.getLastName());
   dto.setMoney(person.getMoney());
   dto.setCreditCards(creditCardService.getAll(person.getId()));
   
   // Add to model list
   personsDTO.add(dto);
     }
     
     // Add to model
     model.addAttribute("persons", personsDTO);

     // This will resolve to /WEB-INF/jsp/records.jsp
  return "records";
 }

PersonDTO acts as a data model for the records.jsp view.

PersonDTO.java

package org.krams.tutorial.dto;

import java.util.List;

import org.krams.tutorial.domain.CreditCard;

/**
 * Data Transfer Object for displaying purposes
 */
public class PersonDTO {

 private Integer id;
 private String firstName;
 private String lastName;
 private Double money;
 private List<CreditCard> creditCards;
 
 public Integer getId() {
  return id;
 }
 public void setId(Integer id) {
  this.id = id;
 }
 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;
 }
 public List<CreditCard> getCreditCards() {
  return creditCards;
 }
 public void setCreditCards(List<CreditCard> creditCards) {
  this.creditCards = creditCards;
 }
}

CreditCardController
CreditCardController is responsible for handling request for credit card records. We won't be using all methods available in this controller. They had been added for the sake of completeness.

CreditCardController.java

package org.krams.tutorial.controller;

import javax.annotation.Resource;

import org.apache.log4j.Logger;
import org.krams.tutorial.domain.CreditCard;
import org.krams.tutorial.service.CreditCardService;
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 credit card requests
 * 
 * @author Krams at {@link http://krams915@blogspot.com
 */
@Controller
@RequestMapping("/main/creditcard")
public class CreditCardController {

 protected static Logger logger = Logger.getLogger("controller");
 
 @Resource(name="creditCardService")
 private CreditCardService creditCardService;
 
    /**
     * Retrieves the "Add New Credit Card" page
     */
    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public String getAdd(@RequestParam("id") Integer personId, Model model) {
     logger.debug("Received request to show add page");
    
     // Prepare model object
     CreditCard creditCard = new CreditCard();
     
     // Add to model
     model.addAttribute("personId", personId);
     model.addAttribute("creditCardAttribute", creditCard);

     // This will resolve to /WEB-INF/jsp/add-credit-card.jsp
     return "add-credit-card";
 }
 
    /**
     * Adds a new credit card
     */
    @RequestMapping(value = "/add", method = RequestMethod.POST)
    public String postAdd(@RequestParam("id") Integer personId, 
              @ModelAttribute("creditCardAttribute") CreditCard creditCard) {
  logger.debug("Received request to add new credit card");
  
  // Delegate to service
  creditCardService.add(personId, creditCard);

  // Redirect to url
  return "redirect:/krams/main/record/list";
 }
    
    
    /**
     * Deletes a credit card
     */
    @RequestMapping(value = "/delete", method = RequestMethod.GET)
    public String getDelete(@RequestParam("id") Integer creditCardId) {
     logger.debug("Received request to delete credit card");
    
     
     // Delegate to service
  creditCardService.delete(creditCardId);

  // Redirect to url
  return "redirect:/krams/main/record/list";
 }
   
    /**
     * Retrieves the "Edit Existing Credit Card" page
     */
    @RequestMapping(value = "/edit", method = RequestMethod.GET)
    public String getEdit(@RequestParam("pid") Integer personId, 
      @RequestParam("cid") Integer creditCardId, Model model) {
     logger.debug("Received request to show edit page");
     
     // Retrieve credit card by id
     CreditCard existingCreditCard = creditCardService.get(creditCardId);

     // Add to model
     model.addAttribute("personId", personId);
     model.addAttribute("creditCardAttribute", existingCreditCard);

     // This will resolve to /WEB-INF/jsp/edit-credit-card.jsp
     return "edit-credit-card";
 }
 
    /**
     * Edits an existing credit card
     */
    @RequestMapping(value = "/edit", method = RequestMethod.POST)
    public String postEdit(@RequestParam("id") Integer creditCardId, 
              @ModelAttribute("creditCardAttribute") CreditCard creditCard) {
  logger.debug("Received request to add new credit card");
  
  // Assign id
  creditCard.setId(creditCardId);
  
  // Delegate to service
  creditCardService.edit(creditCard);

  // Redirect to url
  return "redirect:/krams/main/record/list";
 }
}

View Layer

After discussing the Domain, Service, and Controller layers, we'll now turn our focus to the View layer. Our views are primarily composed of JSP pages. Here are the JSPs:

Show all records

records.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>Records</h1>

<c:url var="editImgUrl" value="/resources/img/edit.png" />
<c:url var="deleteImgUrl" value="/resources/img/delete.png" />
<c:url var="addUrl" value="/krams/main/record/add" />
<table style="border: 1px solid; width: 100%; text-align:center">
 <thead style="background:#d3dce3">
  <tr>
   <th>Id</th>
   <th>First Name</th>
   <th>Last Name</th>
   <th>Money</th>
   <th colspan="2"></th>
   <th>CC Type</th>
   <th>CC Number</th>
   <th colspan="3"></th>
  </tr>
 </thead>
 <tbody style="background:#ccc">
 <c:forEach items="${persons}" var="person">
  <c:url var="editUrl" value="/krams/main/record/edit?id=${person.id}" />
  <c:url var="deleteUrl" value="/krams/main/record/delete?id=${person.id}" />
  
  <c:if test="${!empty person.creditCards}">
   <c:forEach items="${person.creditCards}" var="creditCard">
   <tr>
    <td><c:out value="${person.id}" /></td>
    <td><c:out value="${person.firstName}" /></td>
    <td><c:out value="${person.lastName}" /></td>
    <td><c:out value="${person.money}" /></td>
    <td><a href="${editUrl}"><img src="${editImgUrl}"></img></a></td>
    <td><a href="${deleteUrl}"><img src="${deleteImgUrl}"></img></a></td>
    
    <td><c:out value="${creditCard.type}" /></td>
    <td><c:out value="${creditCard.number}" /></td>
    <c:url var="addCcUrl" value="/krams/main/creditcard/add?id=${person.id}" />
    <c:url var="editCcUrl" value="/krams/main/creditcard/edit?pid=${person.id}&cid=${creditCard.id}" />
    <c:url var="deleteCcUrl" value="/krams/main/creditcard/delete?id=${creditCard.id}" />
    <td><a href="${addCcUrl}">+</a></td>
    <td><a href="${editCcUrl}"><img src="${editImgUrl}"></img></a></td>
    <td><a href="${deleteCcUrl}"><img src="${deleteImgUrl}"></img></a></td>
   </tr>
   </c:forEach>
  </c:if>
  
  <c:if test="${empty person.creditCards}">
   <tr>
    <td><c:out value="${person.id}" /></td>
    <td><c:out value="${person.firstName}" /></td>
    <td><c:out value="${person.lastName}" /></td>
    <td><c:out value="${person.money}" /></td>
    <td><a href="${editUrl}"><img src="${editImgUrl}"></img></a></td>
    <td><a href="${deleteUrl}"><img src="${deleteImgUrl}"></img></a></td>
    
    <td>N/A</td>
    <td>N/A</td>
    <c:url var="addCcUrl" value="/krams/main/creditcard/add?id=${person.id}" />
    <td><a href="${addCcUrl}">+</a></td>
    <td></td>
    <td></td>
   </tr>
  </c:if>
  
 </c:forEach>
 </tbody>
</table>

<c:if test="${empty persons}">
 No records found. 
</c:if>

<p><a href="${addUrl}">Create new record</a></p>

</body>
</html>

Add new record

add-record.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Create New Record</h1>

<c:url var="saveUrl" value="/krams/main/record/add" />
<form:form modelAttribute="personAttribute" method="POST" action="${saveUrl}">
 <table>
  <tr>
   <td><form:label path="firstName">First Name:</form:label></td>
   <td><form:input path="firstName"/></td>
  </tr>

  <tr>
   <td><form:label path="lastName">Last Name</form:label></td>
   <td><form:input path="lastName"/></td>
  </tr>
  
  <tr>
   <td><form:label path="money">Money</form:label></td>
   <td><form:input path="money"/></td>
  </tr>
 </table>
 
 <input type="submit" value="Save" />
</form:form>

</body>
</html>

Edit existing record

edit-record.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Edit Existing Record</h1>

<c:url var="saveUrl" value="/krams/main/record/edit?id=${personAttribute.id}" />
<form:form modelAttribute="personAttribute" method="POST" action="${saveUrl}">
 <table>
  <tr>
   <td><form:label path="id">Id:</form:label></td>
   <td><form:input path="id" disabled="true"/></td>
  </tr>
 
  <tr>
   <td><form:label path="firstName">First Name:</form:label></td>
   <td><form:input path="firstName"/></td>
  </tr>

  <tr>
   <td><form:label path="lastName">Last Name</form:label></td>
   <td><form:input path="lastName"/></td>
  </tr>
  
  <tr>
   <td><form:label path="money">Money</form:label></td>
   <td><form:input path="money"/></td>
  </tr>
 </table>
 
 <input type="submit" value="Save" />
</form:form>

</body>
</html>

Add new credit card

add-credit-card.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Add New Credit Card</h1>

<c:url var="saveUrl" value="/krams/main/creditcard/add?id=${personId}" />
<form:form modelAttribute="creditCardAttribute" method="POST" action="${saveUrl}">
 <table>
 
  <tr>
   <td>Person Id:</td>
   <td><input type="text" value="${personId}" disabled="true"/>
  </tr>
  
  <tr>
   <td><form:label path="type">Type:</form:label></td>
   <td><form:input path="type"/></td>
  </tr>

  <tr>
   <td><form:label path="number">Number:</form:label></td>
   <td><form:input path="number"/></td>
  </tr>
 </table>
 
 <input type="submit" value="Save" />
</form:form>

</body>
</html>

Edit existing credit card

edit-credit-card.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Edit Existing Credit Card</h1>

<c:url var="saveUrl" value="/krams/main/creditcard/edit?id=${creditCardAttribute.id}" />
<form:form modelAttribute="creditCardAttribute" method="POST" action="${saveUrl}">
 <table>
 
  <tr>
   <td>Person Id:</td>
   <td><input type="text" value="${personId}" disabled="true"/>
  </tr>
  
  <tr>
   <td><form:label path="type">Type:</form:label></td>
   <td><form:input path="type"/></td>
  </tr>

  <tr>
   <td><form:label path="number">Number:</form:label></td>
   <td><form:input path="number"/></td>
  </tr>
 </table>
 
 <input type="submit" value="Save" />
</form:form>

</body>
</html>

Configuration

We have completed the necessary Java classes. Our next step is to declare the necessary configuration files:

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 
 <servlet>
  <servlet-name>spring</servlet-name>
  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
  <load-on-startup>1</load-on-startup>
 </servlet>
 
 <servlet-mapping>
  <servlet-name>spring</servlet-name>
  <url-pattern>/krams/*</url-pattern>
 </servlet-mapping>

 <listener>
  <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 </listener>
 
</web-app>

spring-servlet.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" 
 xsi:schemaLocation="http://www.springframework.org/schema/beans 
      http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
 
 <!-- Declare a view resolver -->
 <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver" 
      p:prefix="/WEB-INF/jsp/" p:suffix=".jsp" />

</beans>

applicationContext.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:context="http://www.springframework.org/schema/context"
 xmlns:mvc="http://www.springframework.org/schema/mvc"
 xsi:schemaLocation="http://www.springframework.org/schema/beans 
      http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
      http://www.springframework.org/schema/context
      http://www.springframework.org/schema/context/spring-context-3.0.xsd
   http://www.springframework.org/schema/mvc 
   http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd">
 
 <!-- Activates various annotations to be detected in bean classes -->
 <context:annotation-config />
 
 <!-- Scans the classpath for annotated components that will be auto-registered as Spring beans.
  For example @Controller and @Service. Make sure to set the correct base-package-->
 <context:component-scan base-package="org.krams.tutorial" />
 
 <!-- Configures the annotation-driven Spring MVC Controller programming model.
 Note that, with Spring 3.0, this tag works in Servlet MVC only!  -->
 <mvc:annotation-driven /> 
 
 <!-- Load Hibernate related configuration -->
 <import resource="hibernate-context.xml" />
 
</beans>

hibernate-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:tx="http://www.springframework.org/schema/tx"
        xmlns:context="http://www.springframework.org/schema/context"
        xsi:schemaLocation="
   http://www.springframework.org/schema/beans 
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/tx 
   http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
   http://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context-3.0.xsd
      ">

 <context:property-placeholder location="/WEB-INF/spring.properties" />
    
    <!-- Enable annotation style of managing transactions -->
 <tx:annotation-driven transaction-manager="transactionManager" /> 
   
    <!-- Declare the Hibernate SessionFactory for retrieving Hibernate sessions -->
    <!-- See http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/orm/hibernate3/annotation/AnnotationSessionFactoryBean.html -->        
 <!-- See http://docs.jboss.org/hibernate/stable/core/api/index.html?org/hibernate/SessionFactory.html -->
 <!-- See http://docs.jboss.org/hibernate/stable/core/api/index.html?org/hibernate/Session.html -->
 <bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"
     p:dataSource-ref="dataSource"
     p:configLocation="${hibernate.config}"
     p:packagesToScan="org.krams.tutorial"/>
 
 <!-- Declare a datasource that has pooling capabilities-->  
 <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
    destroy-method="close"
    p:driverClass="${app.jdbc.driverClassName}"
    p:jdbcUrl="${app.jdbc.url}"
    p:user="${app.jdbc.username}"
    p:password="${app.jdbc.password}"
    p:acquireIncrement="5"
    p:idleConnectionTestPeriod="60"
    p:maxPoolSize="100"
    p:maxStatements="50"
    p:minPoolSize="10" />

 <!-- Declare a transaction manager-->
 <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager" 
          p:sessionFactory-ref="sessionFactory" />
  
</beans>

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
  "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
  "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
  
<hibernate-configuration>
  <session-factory>
   <!-- We're using MySQL database so the dialect needs to MySQL as well-->
    <property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
    <!-- Enable this to see the SQL statements in the logs-->
    <property name="show_sql">true</property>
    <!-- This will drop our existing database and re-create a new one.
      Existing data will be deleted! -->
    <property name="hbm2ddl.auto">create</property>
  </session-factory>
</hibernate-configuration>

spring.properties

# database properties
app.jdbc.driverClassName=com.mysql.jdbc.Driver
app.jdbc.url=jdbc:mysql://localhost/mydatabase
app.jdbc.username=root
app.jdbc.password=

#hibernate properties
hibernate.config=/WEB-INF/hibernate.cfg.xml

Run the Application

Setup the database

Our application uses MySQL as its database. To run the application, make sure to setup the database first.

To create the database, follow these steps.
1. Open phpmyadmin (or any tool you prefer with)
2. Create a new database named mydatabase
3. Run the application to automatically create the database schema.

To populate the database with sample data, import the mydatabase.sql SQL script which is located under the WEB-INF folder of the application:

Access the main application

To access the main application, use the following URL:

http://localhost:8080/spring-hibernate-one-to-many-default/krams/main/record/list

You should see the following application:

Conclusion

That's it. We've successfully created a Spring MVC application and implemented a one-to-many association in Hibernate using annotations. We've also discussed issues and solutions when using default settings of @OneToMany annotation.

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

You can download the project as a Maven build. Look for the spring-hibernate-one-to-many-default.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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Saturday, January 8, 2011

Spring MVC 3, Hibernate Annotations, MySQL Integration Tutorial

In this tutorial we will build a simple Spring MVC 3 application for managing a list of persons. We will provide a simple CRUD system for viewing, adding, editing, and deleting of persons. For the persistence layer, we will use Hibernate 3 annotations and use MySQL as our database, though the application is flexible enough to utilize different databases. A prior knowledge of MVC, ORM, and SQL is assumed in this tutorial. This tutorial is similar with Spring 3 MVC - Hibernate 3: Using Annotations Integration Tutorial

Spring MVC 3 and Hibernate Tutorials Series
Spring - Hibernate: Many-To-One Association - Explicitly Specify Join Table, Cascade, and Fetch
Spring - Hibernate: One-To-Many Association - Explicitly Specify Join Table, Cascade, and Fetch
Spring - Hibernate: Many-To-One Association
Spring - Hibernate: One-To-Many Association
Spring MVC 3, Hibernate Annotations, MySQL Integration Tutorial
Spring MVC 3, Hibernate Annotations, HSQLDB Integration Tutorial

What is Hibernate?

Hibernate is an object-relational mapping (ORM) library for the Java language, providing a framework for mapping an object-oriented domain model to a traditional relational database. Hibernate solves object-relational impedance mismatch problems by replacing direct persistence-related database accesses with high-level object handling functions

Source: http://en.wikipedia.org/wiki/Hibernate_(Java)

What is MySQL?

The MySQL Database powers the most demanding Web, E-commerce and Online Transaction Processing (OLTP) applications. It is a fully integrated transaction-safe, ACID compliant database with full commit, rollback, crash recovery and row level locking capabilities. MySQL delivers the ease of use, scalability, and performance that has made MySQL the world's most popular open source database. Some of the world's most trafficked websites like Facebook, Google, ticketmaster, and eBay rely on MySQL for their business critical applications.

Source: http://www.mysql.com/products/enterprise/database/

Let's preview first the final structure of our project.

And here's how our application would look like:

It's a simple, crude CRUD system (pun intended).

We start by defining our domain object Person

Person

package org.krams.tutorial.domain;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * For a complete reference see 
 * 
 * Hibernate Annotations Communit Documentations
 */
@Entity
@Table(name = "PERSON")
public class Person implements Serializable {

 private static final long serialVersionUID = -5527566248002296042L;
 
 @Id
 @Column(name = "ID")
 @GeneratedValue
 private Integer id;
 
 @Column(name = "FIRST_NAME")
 private String firstName;
 
 @Column(name = "LAST_NAME")
 private String lastName;
 
 @Column(name = "MONEY")
 private Double money;

 public Integer getId() {
  return id;
 }

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

 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;
 }
}

Person is a simple POJO containing four private fields:

id
firstName
lastName
money

Each of these fields have been annotated with @Column and assigned with corresponding names.

ID
FIRST_NAME
LAST_NAME
MONEY

These column names are database column names. You don't deal with them. Instead, Hibernate is the one responsible for managing your database. However, you are responsible for declaring the column names in the POJO. You don't declare them in your database. Remember your database doesn't exist yet.

The POJO has been annotated to map to a database table. If you look at the declaration of the Person class we see the annotation @Table and the name of the actual table:

@Entity
@Table(name = "PERSON")
public class Person implements Serializable

Notice the annotation @Entity before the @Table. This tells Hibernate that this POJO should be mapped to a database table.

Since we will manipulate a list of persons, let's declare a service that manipulates a list of Persons.

PersonService

package org.krams.tutorial.service;

import java.util.List;

import javax.annotation.Resource;

import org.apache.log4j.Logger;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.krams.tutorial.domain.Person;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

/**
 * Service for processing Persons
 * 
 */
@Service("personService")
@Transactional
public class PersonService {

 protected static Logger logger = Logger.getLogger("service");
 
 @Resource(name="sessionFactory")
 private SessionFactory sessionFactory;
 
 /**
  * Retrieves all persons
  * 
  * @return a list of persons
  */
 public List getAll() {
  logger.debug("Retrieving all persons");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Create a Hibernate query (HQL)
  Query query = session.createQuery("FROM  Person");
  
  // Retrieve all
  return  query.list();
 }
 
 /**
  * Retrieves a single person
  */
 public Person get( Integer id ) {
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Retrieve existing person first
  Person person = (Person) session.get(Person.class, id);
  
  return person;
 }
 /**
  * Adds a new person
  */
 public void add(Person person) {
  logger.debug("Adding new person");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Save
  session.save(person);
 }
 
 /**
  * Deletes an existing person
  * @param id the id of the existing person
  */
 public void delete(Integer id) {
  logger.debug("Deleting existing person");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Retrieve existing person first
  Person person = (Person) session.get(Person.class, id);
  
  // Delete 
  session.delete(person);
 }
 
 /**
  * Edits an existing person
  */
 public void edit(Person person) {
  logger.debug("Editing existing person");
  
  // Retrieve session from Hibernate
  Session session = sessionFactory.getCurrentSession();
  
  // Retrieve existing person via id
  Person existingPerson = (Person) session.get(Person.class, person.getId());
  
  // Assign updated values to this person
  existingPerson.setFirstName(person.getFirstName());
  existingPerson.setLastName(existingPerson.getLastName());
  existingPerson.setMoney(existingPerson.getMoney());

  // Save updates
  session.save(existingPerson);
 }
}

We've declared a simple CRUD system with the following methods:

getAll()
add()
delete()
edit()

In each method we retrieve the session:

Session session = sessionFactory.getCurrentSession();

This is similar to retrieving a connection from the database so that we can do our work. The Session object provides numerous methods for persisting objects. For this tutorial, we use the following Session methods:

session.createQuery()
session.save()
session.delete()

We're done with the domain and the service layer. Let's move to the Spring controller.

MainController

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
 */
@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="id", required=true) Integer 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("id", 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="id", required=true) Integer 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="id", required=true) Integer 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.setId(id);
     
     // Delegate to PersonService for editing
     personService.edit(person);
     
     // Add id reference to Model
  model.addAttribute("id", id);
  
     // This will resolve to /WEB-INF/jsp/editedpage.jsp
  return "editedpage";
 }
    
}

This controller declares the following mappings:

/persons - for retrieving all persons
/persons/add (GET) - displays the Add New form
/persons/add (POST) - saves the new person
/persons/delete - deletes an existing person
/persons/edit (GET) - displays the Edit form
/persons/edit (POST) - saves the edited person

Each mapping delegates the call to the PersonService. When the PersonService is done processing, the controller then forwards the request to a JSP page that displays a confirmation message. Here are the JSP pages.

personspage.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>Persons</h1>

<c:url var="addUrl" value="/krams/main/persons/add" />
<table style="border: 1px solid; width: 500px; text-align:center">
 <thead style="background:#fcf">
  <tr>
   <th>First Name</th>
   <th>Last Name</th>
   <th>Money</th>
   <th colspan="3"></th>
  </tr>
 </thead>
 <tbody>
 <c:forEach items="${persons}" var="person">
   <c:url var="editUrl" value="/krams/main/persons/edit?id=${person.id}" />
   <c:url var="deleteUrl" value="/krams/main/persons/delete?id=${person.id}" />
  <tr>
   <td><c:out value="${person.firstName}" /></td>
   <td><c:out value="${person.lastName}" /></td>
   <td><c:out value="${person.money}" /></td>
   <td><a href="${editUrl}">Edit</a></td>
   <td><a href="${deleteUrl}">Delete</a></td>
   <td><a href="${addUrl}">Add</a></td>
  </tr>
 </c:forEach>
 </tbody>
</table>

<c:if test="${empty persons}">
 There are currently no persons in the list. <a href="${addUrl}">Add</a> a person.
</c:if>

</body>
</html>

editpage.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Edit Person</h1>

<c:url var="saveUrl" value="/krams/main/persons/edit?id=${personAttribute.id}" />
<form:form modelAttribute="personAttribute" method="POST" action="${saveUrl}">
 <table>
  <tr>
   <td><form:label path="id">Id:</form:label></td>
   <td><form:input path="id" disabled="true"/></td>
  </tr>
 
  <tr>
   <td><form:label path="firstName">First Name:</form:label></td>
   <td><form:input path="firstName"/></td>
  </tr>

  <tr>
   <td><form:label path="lastName">Last Name</form:label></td>
   <td><form:input path="lastName"/></td>
  </tr>
  
  <tr>
   <td><form:label path="money">Money</form:label></td>
   <td><form:input path="money"/></td>
  </tr>
 </table>
 
 <input type="submit" value="Save" />
</form:form>

</body>
</html>

addpage.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Create New Person</h1>

<c:url var="saveUrl" value="/krams/main/persons/add" />
<form:form modelAttribute="personAttribute" method="POST" action="${saveUrl}">
 <table>
  <tr>
   <td><form:label path="firstName">First Name:</form:label></td>
   <td><form:input path="firstName"/></td>
  </tr>

  <tr>
   <td><form:label path="lastName">Last Name</form:label></td>
   <td><form:input path="lastName"/></td>
  </tr>
  
  <tr>
   <td><form:label path="money">Money</form:label></td>
   <td><form:input path="money"/></td>
  </tr>
 </table>
 
 <input type="submit" value="Save" />
</form:form>

</body>
</html>

editedpage.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page import="java.util.Date" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Persons</h1>

<p>You have edited a person with id ${id} at <%= new java.util.Date() %></p>

<c:url var="mainUrl" value="/krams/main/persons" />
<p>Return to <a href="${mainUrl}">Main List</a></p>

</body>
</html>

addedpage.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page import="java.util.Date" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Persons</h1>

<p>You have added a new person at <%= new java.util.Date() %></p>

<c:url var="mainUrl" value="/krams/main/persons" />
<p>Return to <a href="${mainUrl}">Main List</a></p>

</body>
</html>

deletedpage.jsp

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page import="java.util.Date" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

<h1>Persons</h1>

<p>You have deleted a person with id ${id} at <%= new java.util.Date() %></p>

<c:url var="mainUrl" value="/krams/main/persons" />
<p>Return to <a href="${mainUrl}">Main List</a></p>

</body>
</html>

Let's complete our Spring MVC application by declaring the required configurations.

To enable Spring MVC we need to add in the web.xml

web.xml

<servlet>
  <servlet-name>spring</servlet-name>
  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
  <load-on-startup>1</load-on-startup>
 </servlet>
 
 <servlet-mapping>
  <servlet-name>spring</servlet-name>
  <url-pattern>/krams/*</url-pattern>
 </servlet-mapping>

 <listener>
  <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 </listener>

Take note of the URL pattern. When accessing any pages in our MVC application, the host name must be appended with

/krams

In the web.xml we declared a servlet-name spring. By convention, we must declare a spring-servlet.xml as well.

spring-servlet.xml

<!-- Declare a view resolver -->
 <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver" 
      p:prefix="/WEB-INF/jsp/" p:suffix=".jsp" />

By convention, we must declare an applicationContext.xml as well.

applicationContext.xml

<!-- Activates various annotations to be detected in bean classes -->
 <context:annotation-config />
 
 <!-- Scans the classpath for annotated components that will be auto-registered as Spring beans.
  For example @Controller and @Service. Make sure to set the correct base-package-->
 <context:component-scan base-package="org.krams.tutorial" />
 
 <!-- Configures the annotation-driven Spring MVC Controller programming model.
 Note that, with Spring 3.0, this tag works in Servlet MVC only!  -->
 <mvc:annotation-driven /> 
 
 <!-- Load Hibernate related configuration -->
 <import resource="hibernate-context.xml" />

Notice in the applicationContext.xml, we declared the following import:

<import resource="hibernate-context.xml" />

This contains the Hibernate configuration files

<?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:tx="http://www.springframework.org/schema/tx"
        xmlns:context="http://www.springframework.org/schema/context"
        xsi:schemaLocation="
   http://www.springframework.org/schema/beans 
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/tx 
   http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
   http://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context-3.0.xsd
      ">

 <context:property-placeholder location="/WEB-INF/spring.properties" />
    
    <!-- Enable annotation style of managing transactions -->
 <tx:annotation-driven transaction-manager="transactionManager" /> 
   
    <!-- Declare the Hibernate SessionFactory for retrieving Hibernate sessions -->
    <!-- See http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/orm/hibernate3/annotation/AnnotationSessionFactoryBean.html -->        
 <!-- See http://docs.jboss.org/hibernate/stable/core/api/index.html?org/hibernate/SessionFactory.html -->
 <!-- See http://docs.jboss.org/hibernate/stable/core/api/index.html?org/hibernate/Session.html -->
 <bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"
     p:dataSource-ref="dataSource"
     p:configLocation="${hibernate.config}"
     p:packagesToScan="org.krams.tutorial"/>
 
 <!-- Declare a datasource that has pooling capabilities-->  
 <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
    destroy-method="close"
    p:driverClass="${app.jdbc.driverClassName}"
    p:jdbcUrl="${app.jdbc.url}"
    p:user="${app.jdbc.username}"
    p:password="${app.jdbc.password}"
    p:acquireIncrement="5"
    p:idleConnectionTestPeriod="60"
    p:maxPoolSize="100"
    p:maxStatements="50"
    p:minPoolSize="10" />

 <!-- Declare a transaction manager-->
 <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager" 
          p:sessionFactory-ref="sessionFactory" />
  
</beans>

We basically encapsulated all Hibernate and Spring related configurations in this one XML file. Here's what happening within the config:

1. Enable transaction support through Spring annotations:

<tx:annotation-driven transaction-manager="transactionManager" />

2. Declare the Hibernate SessionFactory:

<bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"
     p:dataSource-ref="dataSource"
     p:configLocation="${hibernate.config}"
     p:packagesToScan="org.krams.tutorial"/>

A SessionFactory is a factory that produces Session objects. It's analogous to a real Car Factory or Car Assemblies where its job is to make cars for humans.

What is a Session?

The main function of the Session is to offer create, read and delete operations for instances of mapped entity classes.

Source: http://docs.jboss.org/hibernate/stable/core/api/index.html?org/hibernate/Session.html

A SessionFactory requires a datasource. The datasource in this tutorial is the database.

A SessionFactory requires a configLocation. The configLocation contains Hibernate-specific configurations. Here's our Hibernate-specific config file:

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
  "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
  "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
  
<hibernate-configuration>
  <session-factory>
   <!-- We're using MySQL database so the dialect needs to MySQL as well-->
    <property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
    <!-- Enable this to see the SQL statements in the logs-->
    <property name="show_sql">false</property>
    <!-- This will drop our existing database and re-create a new one.
      Existing data will be deleted! -->
    <property name="hbm2ddl.auto">create</property>
  </session-factory>
</hibernate-configuration>

Here we declared the type of database to be used. We are using MySQL so we use a MySQL dialect. We're using a specialized MySQL5InnoDBDialect because we decided to use the InnoDB storage engine for MySQL.

What's MySQL InnoDB?

InnoDB is a transaction-safe (ACID compliant) storage engine for MySQL that has commit, rollback, and crash-recovery capabilities to protect user data.

Source: http://dev.mysql.com/doc/refman/5.0/en/innodb-storage-engine.html

Returning back to the SessionFactory bean declaration, it also requires the property packagesToScan. This is to indicate where our annotated entities are located. In this tutorial, it's under the org.krams.tutorial

3. Declare a datasource:

<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
 destroy-method="close"
 p:driverClass="${app.jdbc.driverClassName}"
 p:jdbcUrl="${app.jdbc.url}"
 p:user="${app.jdbc.username}"
 p:password="${app.jdbc.password}"
 p:acquireIncrement="5"
 p:idleConnectionTestPeriod="60"
 p:maxPoolSize="100"
 p:maxStatements="50"
 p:minPoolSize="10" />

Our datasource uses C3P0 for pooling to allow efficient access to our database. Why do we need to wrap our datasource with a connection pool?

JDBC connections are often managed via a connection pool rather than obtained directly from the driver. Examples of connection pools include BoneCP, C3P0 and DBCP.

Source: http://en.wikipedia.org/wiki/Java_Database_Connectivity

What is Pooling?

In software engineering, a connection pool is a cache of database connections maintained so that the connections can be reused when future requests to the database are required. Connection pools are used to enhance the performance of executing commands on a database. Opening and maintaining a database connection for each user, especially requests made to a dynamic database-driven website application, is costly and wastes resources. In connection pooling, after a connection is created, it is placed in the pool and it is used over again so that a new connection does not have to be established.

Source: http://en.wikipedia.org/wiki/Connection_pool

For more info on configuring C3P0, you can check this reference from JBoss: HowTo configure the C3P0 connection pool. For a list of other pooling providers, see Open Source Database Connection Pools

The database-specific configuration are contained within a properties file.

spring.properties

mydatabase is the name of our MySQL dabatase.

As an alternative, we can enter these properties directly within the hibernate-context.xml

This is exactly similar to the following:

The benefit of using a separate properties file is we encapsulate all database-specific configs within a separate file. The hibernate-context.xml purpose is to encapsulate Hibernate-related config not database properties.

That's it. We've completed our application. We've managed to setup a simple Spring MVC 3 application that uses Hibernate Annotations to encapsulate persistence access to a MySQL database. We've also leveraged Spring's simple MVC programming model.

To access the main page, enter the following URL:

http://localhost:8080/spring-hibernate-mysql/krams/main/persons

The best way to learn further is to try the actual application.

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

You can download the project as a Maven build. Look for the spring-hibernate-mysql.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.