Hibernate Hello World Example in Eclipse (XML Mapping)

In this Hibernate Hello World Example, let’s write our first Hibernate Hello World program which will persist Java object into the database. For configuring a hibernate application,there are some prerequisites which need to be fulfilled

Prerequisites:

  1. Download Hibernate Framework.(Hibernate 4.3.11 used in this example)
  2. IDE (Eclipse in my case)
  3. JDK 1.5 or above
  4. Any database(Oracle 11g)
  5. Driver for Database(ojdbc14.jar)

Creating table

Before we start let’s create a simple table to apply the hibernate operations. Copy and Paste the following SQL query in the query editor to get the table created.

CREATE TABLE "EMPLOYEE" 
   (	"ID" NUMBER(10,0) NOT NULL ENABLE, 
	"NAME" VARCHAR2(255 CHAR), 
	"AGE" NUMBER(10,0), 
	"DEPT" VARCHAR2(255 CHAR), 
	 PRIMARY KEY ("ID")
	 );

Folder Structure:

Hibernate Hello World Example

  1. Create a simple Maven Project “HibernateTutorial” and create a package for our source files com.javainterviewpointunder  src/main/java 
  2. Now add the following dependency in the POM.xml
     <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>HibernateTutorial</groupId>
       <artifactId>HibernateTutorial</artifactId>
       <version>0.0.1-SNAPSHOT</version>
       <properties>
          <hibernate.version>4.3.11.Final</hibernate.version>
          <oracle.connector.version>11.2.0</oracle.connector.version>
       </properties>
    
       <dependencies>
         <!-- Hibernate -->
         <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>${hibernate.version}</version>
         </dependency>
    
         <!-- Oracle -->
         <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc14</artifactId>
            <version>${oracle.connector.version}</version>
         </dependency>
       </dependencies>
       <build>
         <sourceDirectory>src</sourceDirectory>
         <plugins>
           <plugin>
             <artifactId>maven-compiler-plugin</artifactId>
             <version>3.3</version>
             <configuration>
             <source>1.7</source>
             <target>1.7</target>
             </configuration>
           </plugin>
         </plugins>
       </build>
     </project>
  3. Create the Java classes Employee.java and EmployeeHibernateExample.java  under  com.javainterviewpoint folder.
  4. Place the employee.hbm.xml and hibernate.cfg.xml under the src/main/resources  directory

Hibernate Hello World Example

Employee.java

Create a new Java file Employee.java under the package com.javainterviewpoint and add the following code

package com.javainterviewpoint;

import java.io.Serializable;

public class Employee implements Serializable 
{
    private static final long serialVersionUID = -889976693182180703L;
    
    private int id;
    private String name;
    private int age;
    private String dept;
    
    public Employee()
    {
        super();
    }

    public Employee(int id, String name, int age, String dept)
    {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
        this.dept = dept;
    }
    
    public int getId()
    {
        return id;
    }
    public void setId(int id)
    {
        this.id = id;
    }
    public String getName()
    {
        return name;
    }
    public void setName(String name)
    {
        this.name = name;
    }
    public int getAge()
    {
        return age;
    }
    public void setAge(int age)
    {
        this.age = age;
    }
    public String getDept()
    {
        return dept;
    }
    public void setDept(String dept)
    {
        this.dept = dept;
    }
    @Override
    public String toString()
    {
        return "Employee [id=" + id + ", name=" + name + ", age=" + age + ", dept=" + dept + "]";
    }
    @Override
    public int hashCode()
    {
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + ((dept == null) ? 0 : dept.hashCode());
        result = prime * result + id;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj)
    {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Employee other = (Employee) obj;
        if (age != other.age)
            return false;
        if (dept == null)
        {
            if (other.dept != null)
                return false;
        } else if (!dept.equals(other.dept))
            return false;
        if (id != other.id)
            return false;
        if (name == null)
        {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }
}

Our Employee class is a simple POJO class consisting of the getters and setters for the Employee class properties (id, name, age, dept).

employee.hbm.xml

Place the employee.hbm.xml file under the src/main/resources folder

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
  <hibernate-mapping>
    <class name="com.javainterviewpoint.model.Employee" table="EMPLOYEE">
      <id name="id" column="ID">
        <generator class="assigned" />
      </id>
      <property name="name" column="NAME" />
      <property name="age" column="AGE" />
      <property name="dept" column="DEPT" />
    </class>
 </hibernate-mapping>
  • The “employee.hbm.xml” tells hibernate to map “Employee.class” with the “EMPLOYEE” table in the database.
  • Next tag is the <id> tag, this tag tells which column needs to be marked as primary key in the database table, here our id property of the Employee class is the primary key. We have selected the generator as assigned, This is the default generator strategy.
  • If there is  no <generator> tag specified then hibernate by default assumes it as “assigned”. If the generator class is “assigned” then it is the responsibility of the programmer for assigning a value to the primary key.
  • The property name, age, dept are mapped with NAME, AGE, DEPT columns in the table respectively.

hibernate.cfg.xml

Place the hibernate.cfg.xml file also under the src/main/resources folder

 <?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>

 <!-- Database connection settings -->
 <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
 <property name="hibernate.connection.username">root</property>
 <property name="hibernate.connection.password">root</property>
 <property name="hibernate.connection.url">jdbc:oracle:thin:@mydb:40051:dev</property>

 <!-- JDBC connection pool (use the built-in) -->
 <property name="connection.pool_size">1</property>

 <!-- SQL dialect -->
 <property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

 <!-- Echo all executed SQL to stdout -->
 <property name="show_sql">true</property>

 <!-- Drop and re-create the database schema on startup -->
 <property name="hibernate.hbm2ddl.auto">update</property>

 <!-- Mapping file -->
 <mapping resource="employee.hbm.xml" />
 </session-factory>

</hibernate-configuration>
  • First and foremost property is for specifying the JDBC Driver class, in my case it OracleDriver
<property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
  • Give the connection URL for connecting the database and provide username and password for connecting the above database
<property name="hibernate.connection.url">jdbc:oracle:thin:@mydb:40051:dev</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>
  • Specify the connection pool size, this property limits the number of connections in the Hibernate connection pool.
<property name="connection.pool_size">1</property>
  • Dialect Property makes the Hibernate generate the SQL for the corresponding database which is being used. In this example we are using Oracle database hence Oracle query will be generated. If you are using MySQL database then you need to change the dialect accordingly.
<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>
  • The show_sql property will print the executed sql in the console when set to true.
<property name="show_sql">true</property>
  • If the property “hibernate.hbm2ddl.auto” is set to “create”  This will drop and recreate the database schema on every execution. If it is set to “update” then the database schema will be updated every time rather than dropping and recreating.
<property name="hibernate.hbm2ddl.auto">update</property>
  • Under the Mapping resource tag  we need to specify all the mapping file for which we need the table to be created or updated.
<mapping resource="employee.hbm.xml" />

EmployeeHibernateExample.java

package com.javainterviewpoint;

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

public class EmployeeHibernateExample
{
    public static void main(String args[])
    {
        //Reading the hibernate configuration file
        Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
        StandardServiceRegistryBuilder srb = new StandardServiceRegistryBuilder();
        srb.applySettings(configuration.getProperties());
        ServiceRegistry serviceRegistry = srb.build();
        
        //Create SessionFacctory
        SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
        
        //Create Session from SessionFactory
        Session session = sessionFactory.openSession();
        
        //Begin the transaction
        session.beginTransaction();
        
        //Create Employee object
        Employee ee = new Employee();
        
        //Set value to it properties
        ee.setAge(21);
        ee.setId(22);
        ee.setDept("IT");
        ee.setName("JIP");
        
        //Persist the employee object
        session.save(ee);
        
        //Commit the changes
        session.getTransaction().commit();
        //Close the session
        session.close();
    }
}
  • Create the Configuration object and read the configuration file using the configure() method.
Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
  • Get the SessionFactory object through the buildSessionFactory() method of the configuration object.
SessionFactory sessionFactory = configuration.buildSessionFactory(serviceRegistry);
  • openSession() method opens up the new session and begin a new transaction
Session session = sessionFactory.openSession();
session.beginTransaction();
  • Create a new Employee object and set values to its properties
Employee ee = new Employee();
ee.setAge(21);
ee.setId(22);
ee.setDept("IT");
ee.setName("JIP");
  • save() method of the session object will persist the employee object into the database.
session.save(ee);
  • Finally get the transaction and commit the changes and close the session.
session.getTransaction().commit();
session.close();

Console:

INFO: HHH000261: Table found: EMPLOYEE
Oct 11, 2016 5:48:53 PM org.hibernate.tool.hbm2ddl.TableMetadata 
INFO: HHH000037: Columns: [id, age, name, dept]
Oct 11, 2016 5:48:53 PM org.hibernate.tool.hbm2ddl.TableMetadata 
INFO: HHH000108: Foreign keys: []
Oct 11, 2016 5:48:53 PM org.hibernate.tool.hbm2ddl.TableMetadata 
INFO: HHH000126: Indexes: [sys_c0014161]
Oct 11, 2016 5:48:53 PM org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000232: Schema update complete
Hibernate: insert into EMPLOYEE (NAME, AGE, DEPT, ID) values (?, ?, ?, ?)

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