Hibernate Many-to-Many mapping example using @ManyToMany annotation.

CREATE TABLE EMPLOYEES (

	EMP_ID BIGINT NOT NULL AUTO_INCREMENT,
	NAME VARCHAR(252),
	DEPARTMENT VARCHAR(128),
	SALARY BIGINT,
	JOINED_ON TIMESTAMP,
	PRIMARY KEY (EMP_ID)
);

CREATE TABLE PROJECTS (

	PR_ID BIGINT NOT NULL AUTO_INCREMENT,
	NAME VARCHAR(252),
	OWNER VARCHAR(252),
	PRIMARY KEY (PR_ID)
);

CREATE TABLE EMP_ASSIGNMENTS (

	EA_ID BIGINT NOT NULL AUTO_INCREMENT,
	EMP_ID BIGINT,
	PR_ID BIGINT,
	PRIMARY KEY (EA_ID),
	FOREIGN KEY (EMP_ID) REFERENCES EMPLOYEES(EMP_ID),
	FOREIGN KEY (PR_ID) REFERENCES PROJECTS(PR_ID)
);

INSERT INTO EMPLOYEES (EMP_ID, NAME, DEPARTMENT, SALARY, JOINED_ON) VALUES (1, 'Nataraja G', 'Documentation', 10000, CURRENT_TIMESTAMP);
INSERT INTO EMPLOYEES (EMP_ID, NAME, DEPARTMENT, SALARY, JOINED_ON) VALUES (2, 'Amar M', 'Entertainment', 12000, CURRENT_TIMESTAMP);
INSERT INTO EMPLOYEES (EMP_ID, NAME, DEPARTMENT, SALARY, JOINED_ON) VALUES (3, 'Nagesh Y', 'Admin', 25000, CURRENT_TIMESTAMP);
INSERT INTO EMPLOYEES (EMP_ID, NAME, DEPARTMENT, SALARY, JOINED_ON) VALUES (4, 'Vasu V', 'Security', 2500, CURRENT_TIMESTAMP);

INSERT INTO PROJECTS (PR_ID, NAME, OWNER) VALUES (1, 'Ticket Online', 'Bunty');
INSERT INTO PROJECTS (PR_ID, NAME, OWNER) VALUES (2, 'Disco Drum', 'Chanty');
INSERT INTO PROJECTS (PR_ID, NAME, OWNER) VALUES (3, 'Traffic Audit', 'Sonty');

INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (1, 1, 1);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (2, 1, 2);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (3, 1, 3);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (4, 2, 2);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (5, 2, 3);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (6, 3, 1);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (7, 3, 3);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (8, 4, 1);
INSERT INTO EMP_ASSIGNMENTS (EA_ID, EMP_ID, PR_ID) VALUES (9, 3, 2);

<?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>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/java2novice</property>
		<property name="hibernate.connection.username">root</property>
		<property name="hibernate.connection.password">root</property>
		<property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
		<property name="show_sql">false</property>
	</session-factory>
</hibernate-configuration>

package com.java2novice.model;

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

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name="EMPLOYEES")
public class Employee implements Serializable {

	@Id
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	@Column(name="EMP_ID", unique = true, nullable = false)
	private Long empId;

	private String name;

	private String department;

	private Long salary;

	@Column(name="JOINED_ON")
	private Date joinedOn;

	@ManyToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER)
	@JoinTable(
		name = "EMP_ASSIGNMENTS",
		joinColumns = { @JoinColumn(name = "EMP_ID") },
		inverseJoinColumns = { @JoinColumn(name = "PR_ID") }
	)
	private List<Project> empAssignmentList;

	public Long getEmpId() {
		return empId;
	}

	public void setEmpId(Long empId) {
		this.empId = empId;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getDepartment() {
		return department;
	}

	public void setDepartment(String department) {
		this.department = department;
	}

	public Long getSalary() {
		return salary;
	}

	public void setSalary(Long salary) {
		this.salary = salary;
	}

	public Date getJoinedOn() {
		return joinedOn;
	}

	public void setJoinedOn(Date joinedOn) {
		this.joinedOn = joinedOn;
	}

	public List<Project> getEmpAssignmentList() {
		return empAssignmentList;
	}

	public void setEmpAssignmentList(List<Project> empAssignmentList) {
		this.empAssignmentList = empAssignmentList;
	}

	@Override
	public String toString() {

		String resp = this.empId+" | "+this.name+" | "+this.department+" | "+this.salary+" | "+this.joinedOn;

		return resp;
	}
}

package com.java2novice.model;

import java.util.List;

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

@Entity
@Table(name="PROJECTS")
public class Project {

	@Id
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	@Column(name="PR_ID", unique = true, nullable = false)
	private Long prId;

	private String name;

	private String owner;

	@ManyToMany(mappedBy = "empAssignmentList")
	private List<Employee> employees;

	@Override
	public String toString() {

		return this.prId +" | "+ this.name +" | "+ this.owner;
	}

	public Long getPrId() {
		return prId;
	}

	public void setPrId(Long prId) {
		this.prId = prId;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getOwner() {
		return owner;
	}

	public void setOwner(String owner) {
		this.owner = owner;
	}
}

package com.java2novice.hibernate;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;

import com.java2novice.model.Employee;
import com.java2novice.model.Project;

public class HibernateUtil {

	private static SessionFactory sessionFactory = null;

	static {
		try{
			loadSessionFactory();
		}catch(Exception e){
			System.err.println("Exception while initializing hibernate util.. ");
			e.printStackTrace();
		}
	}

	public static void loadSessionFactory(){

		Configuration configuration = new Configuration();
		configuration.configure("/j2n-hibernate.cfg.xml");
		configuration.addAnnotatedClass(Employee.class);
		configuration.addAnnotatedClass(Project.class);
		ServiceRegistry srvcReg = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();
		sessionFactory = configuration.buildSessionFactory(srvcReg);
	}

	public static Session getSession() throws HibernateException {

		Session retSession=null;
	    	try {
	    		retSession = sessionFactory.openSession();
	    	}catch(Throwable t){
			System.err.println("Exception while getting session.. ");
			t.printStackTrace();
	    	}
	    	if(retSession == null) {
	    		System.err.println("session is discovered null");
	    	}

	    	return retSession;
    }
}

package com.java2novice.hibernate;

import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.java2novice.model.Employee;

public class EmployeesDao {

	public List<Employee> getEmployeeList(){

		Session session = null;
		List<Employee> empList = null;
		try {
			session = HibernateUtil.getSession();
			String queryStr = "select emp from Employee emp";
			Query query = session.createQuery(queryStr);
			empList = query.list();
		} catch(Exception ex) {
			ex.printStackTrace();
			// handle exception here
		} finally {
			try {if(session != null) session.close();} catch(Exception ex) {}
		}
		return empList;
	}

	public static void main(String a[]) {

		EmployeesDao empDao = new EmployeesDao();
		List<Employee> empList = empDao.getEmployeeList();
		System.out.println("emp size: "+empList.size());
		System.out.println("---------------------------");
		empList.stream().forEach(e -> {
			System.out.println(e);
			System.out.println("\n-- projects assigned to "+e.getName()+" --");
			e.getEmpAssignmentList().stream().forEach(System.out::println);
			System.out.println("---------------------------");
		});
	}
}

emp size: 4
---------------------------
1 | Nataraja G | Documentation | 10000 | 2017-12-16 11:59:59.0

-- projects assigned to Nataraja G --
1 | Ticket Online | Bunty
2 | Disco Drum | Chanty
3 | Traffic Audit | Sonty
---------------------------
2 | Amar M | Entertainment | 12000 | 2017-12-16 11:59:59.0

-- projects assigned to Amar M --
2 | Disco Drum | Chanty
3 | Traffic Audit | Sonty
---------------------------
3 | Nagesh Y | Admin | 25000 | 2017-12-16 11:59:59.0

-- projects assigned to Nagesh Y --
1 | Ticket Online | Bunty
2 | Disco Drum | Chanty
3 | Traffic Audit | Sonty
---------------------------
4 | Vasu V | Security | 2500 | 2017-12-16 12:00:21.0

-- projects assigned to Vasu V --
1 | Ticket Online | Bunty
---------------------------