Hibernate hello world (initial setup) example.

In this example we are giving steps to configure Hibernate and get records from MySql database using Hibernate session. We are using Hibernate 5.0.0Final version.

Create DB Table

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)
);

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);

DB Employees Table Records:

mysql> select * from employees;
+--------+------------+---------------+--------+---------------------+
| EMP_ID | NAME       | DEPARTMENT    | SALARY | JOINED_ON           |
+--------+------------+---------------+--------+---------------------+
|      1 | Nataraja G | Documentation |  10000 | 2017-12-16 11:59:59 |
|      2 | Amar M     | Entertainment |  12000 | 2017-12-16 11:59:59 |
|      3 | Nagesh Y   | Admin         |  25000 | 2017-12-16 11:59:59 |
|      4 | Vasu V     | Security      |   2500 | 2017-12-16 12:00:21 |
+--------+------------+---------------+--------+---------------------+
4 rows in set (0.00 sec)

Maven pom.xml reference

Here is the reference for the pom.xml will all required dependencies:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.java2novice</groupId>
	<artifactId>hibernate-examples</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>hibernate-examples</name>

	<properties>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
	</properties>

	<dependencies>
		<!-- Hibernate core dependency -->
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-core</artifactId>
			<version>5.0.0.Final</version>
		</dependency>
		<!-- MySQL database driver -->
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>5.1.37</version>
		</dependency>
	</dependencies>
</project>

Hibernate Configuration File

Create hibernate xml based configuration file in your resources folder (classpath). This file includes hibernate configurations like driver class, DB connectivity URL, DB credentials and so on...

j2n-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>
		<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>

Hibernate Mapping with Entity Class

Here is the class Employee which maps to EMPLOYEES table in database.

The table columns are mapped to class member vairables. Use @Column annotation to map DB columns with class variables.

package com.java2novice.model;

import java.util.Date;

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

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

	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	@Column(name="EMP_ID")
	private Long empId;

	private String name;

	private String department;

	private Long salary;

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

	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;
	}

	@Override
	public String toString() {

		return this.empId+" | "+this.name+" | "+this.department+" | "+this.salary+" | "+this.joinedOn;
	}
}

Hibernate Utility Class

This class manages hibernate session.

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;

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);
		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;
    }
}

Hibernate Dao Class

This class makes a request to database using hibernate and reads data.

package com.java2novice.hibernate;

import java.util.List;

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

import com.java2novice.model.Employee;

public class EmployeesDao {

	public List<Employee> getEmployeeList(){

		Session session = null;
		session = HibernateUtil.getSession();
		String queryStr = "select emp from Employee emp";
		Query query = session.createQuery(queryStr);

		return query.list();
	}

	public static void main(String a[]) {

		EmployeesDao empDao = new EmployeesDao();
		List<Employee> empList = empDao.getEmployeeList();
		System.out.println("emp size: "+empList.size());
		empList.stream().forEach(System.out::println);
	}
}

Output:

emp size: 4
1 | Nataraja G | Documentation | 10000 | 2017-12-16 11:59:59.0
2 | Amar M | Entertainment | 12000 | 2017-12-16 11:59:59.0
3 | Nagesh Y | Admin | 25000 | 2017-12-16 11:59:59.0
4 | Vasu V | Security | 2500 | 2017-12-16 12:00:21.0

Next Program >>

Hibernate Examples

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What is abstract class or abstract method?

We cannot create instance for an abstract class. We can able to create instance for its subclass only. By specifying abstract keyword just before class, we can make a class as abstract class.

public abstract class MyAbstractClass{

}

Abstract class may or may not contains abstract methods. Abstract method is just method signature, it does not containes any implementation. Its subclass must provide implementation for abstract methods. Abstract methods are looks like as given below:

public abstract int getLength();

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