The best tutorial - Hibernate Many-to-Many example (Annotation)

See previous post for dependency jar files

Project Structure

Review the new project structure of this tutorial.

1. “Many-to-many” table relationship

2. Hibernate Model Class

Update previous model classes – Stock.java and Category.java, and define new annotation code inside.
File : Stock.java

package com.mkyong.stock;
 
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.CascadeType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;
 
@Entity
@Table(name = "stock", catalog = "mkyongdb", uniqueConstraints = {
  @UniqueConstraint(columnNames = "STOCK_NAME"),
  @UniqueConstraint(columnNames = "STOCK_CODE") })
public class Stock implements java.io.Serializable {
 
 private Integer stockId;
 private String stockCode;
 private String stockName;
 private Set<Category> categories = new HashSet<Category>(0);
 
 public Stock() {
 }
 
 public Stock(String stockCode, String stockName) {
  this.stockCode = stockCode;
  this.stockName = stockName;
 }
 
 public Stock(String stockCode, String stockName, Set<Category> categories) {
  this.stockCode = stockCode;
  this.stockName = stockName;
  this.categories = categories;
 }
 
 @Id
 @GeneratedValue(strategy = IDENTITY)
 @Column(name = "STOCK_ID", unique = true, nullable = false)
 public Integer getStockId() {
  return this.stockId;
 }
 
 public void setStockId(Integer stockId) {
  this.stockId = stockId;
 }
 
 @Column(name = "STOCK_CODE", unique = true, nullable = false, length = 10)
 public String getStockCode() {
  return this.stockCode;
 }
 
 public void setStockCode(String stockCode) {
  this.stockCode = stockCode;
 }
 
 @Column(name = "STOCK_NAME", unique = true, nullable = false, length = 20)
 public String getStockName() {
  return this.stockName;
 }
 
 public void setStockName(String stockName) {
  this.stockName = stockName;
 }
 
 @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
 @JoinTable(name = "stock_category", catalog = "mkyongdb", joinColumns = { 
   @JoinColumn(name = "STOCK_ID", nullable = false, updatable = false) }, 
   inverseJoinColumns = { @JoinColumn(name = "CATEGORY_ID", 
     nullable = false, updatable = false) })
 public Set<Category> getCategories() {
  return this.categories;
 }
 
 public void setCategories(Set<Category> categories) {
  this.categories = categories;
 }
 
}

File : Category.java

package com.mkyong.stock;
 
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import static javax.persistence.GenerationType.IDENTITY;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
 
@Entity
@Table(name = "category", catalog = "mkyongdb")
public class Category implements java.io.Serializable {
 
 private Integer categoryId;
 private String name;
 private String desc;
 private Set<Stock> stocks = new HashSet<Stock>(0);
 
 public Category() {
 }
 
 public Category(String name, String desc) {
  this.name = name;
  this.desc = desc;
 }
 
 public Category(String name, String desc, Set<Stock> stocks) {
  this.name = name;
  this.desc = desc;
  this.stocks = stocks;
 }
 
 @Id
 @GeneratedValue(strategy = IDENTITY)
 @Column(name = "CATEGORY_ID", unique = true, nullable = false)
 public Integer getCategoryId() {
  return this.categoryId;
 }
 
 public void setCategoryId(Integer categoryId) {
  this.categoryId = categoryId;
 }
 
 @Column(name = "NAME", nullable = false, length = 10)
 public String getName() {
  return this.name;
 }
 
 public void setName(String name) {
  this.name = name;
 }
 
 @Column(name = "[DESC]", nullable = false)
 public String getDesc() {
  return this.desc;
 }
 
 public void setDesc(String desc) {
  this.desc = desc;
 }
 
 @ManyToMany(fetch = FetchType.LAZY, mappedBy = "categories")
 public Set<Stock> getStocks() {
  return this.stocks;
 }
 
 public void setStocks(Set<Stock> stocks) {
  this.stocks = stocks;
 }
 
}

3. Hibernate Configuration File

Puts annotated classes Stock.java and Category.java in hibernate.cfg.xml like this :
File : hibernate.cfg.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 
<hibernate-configuration>
<session-factory>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/mkyongdb</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password">password</property>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="show_sql">true</property>
    <mapping class="com.mkyong.stock.Stock" />
    <mapping class="com.mkyong.stock.Category" />
</session-factory>
</hibernate-configuration>

4. Run It

Run it, the result is self-explanatory.
File : App.java
package com.mkyong.util;

import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.mkyong.stock.Category;
import com.mkyong.stock.Stock;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;

public class App {
    private static SessionFactory factory;
    private static ServiceRegistry serviceRegistry;

    public static void main(String[] args) {

        try {
             Configuration configuration = new Configuration();
             configuration.configure().setProperty("hibernate.show_sql", "false");
             serviceRegistry = new ServiceRegistryBuilder().applySettings(
             configuration.getProperties()).buildServiceRegistry();
             factory = configuration.buildSessionFactory(serviceRegistry);
        } catch (Throwable ex) {
             System.err.println("Failed to create sessionFactory object." + ex);
             throw new ExceptionInInitializerError(ex);
        }
  
        System.out.println("**Example : Hibernate 4 SessionFactory**");
        System.out.println("----------------------------------------");
      
        System.out.println("Hibernate many to many (Annotation)");
        
        Session session = factory.openSession();
  
        //Add data into tables
        add(session);
                  
        //Query data from tables
        query(session);

        session.close();
  
        System.out.println("Done");
    }//End of main
  
    @SuppressWarnings("rawtypes")
    private static void query(Session session) {
        Transaction tx = null;
      
        try {
            tx = session.beginTransaction();
            List employees = session.createQuery("FROM Stock").list();
            for (Iterator iterator = employees.iterator(); iterator.hasNext();) {
                Stock stock = (Stock) iterator.next();
                System.out.println("Code: " + stock.getStockCode());
                System.out.println("Name: " + stock.getStockName());
            }
            tx.commit();
        } catch (HibernateException e) {
          
            if (tx != null)
                tx.rollback();
            e.printStackTrace();
        }
    }
  
    private static void add(Session session) {
        Transaction tx = null;
      
        try {
            tx = session.beginTransaction();
            Stock stock = new Stock();
          
            stock.setStockCode("7052");
            stock.setStockName("PADINI");
        
            Category category1 = new Category("CONSUMER", "CONSUMER COMPANY");
            Category category2 = new Category("INVESTMENT", "INVESTMENT COMPANY");
        
            Set<Category> categories = new HashSet<Category>();
            categories.add(category1);
            categories.add(category2);
        
            stock.setCategories(categories);
        
            session.save(stock);
              
            tx.commit();
        } catch (HibernateException e) {
          
            if (tx != null)
                tx.rollback();
            e.printStackTrace();
        }
    }
}

(Source: Internet)