In this tutorial we will show how you can create an Hibernate application using annotations. For this purpose we will use a basic Maven 3 archetype and we will enhance so that it uses Hibernate dependencies and MySQL as database.
Project setup
There can be several starting points for setting up an Hibernate projects with Maven. The bare bones approach could be using the maven-archetype-quickstart and then updating the pom.xml file with all Hibernate dependencies.
Provided that you have successfully installed Maven, let’s create the project HibernateExample with the following command:
mvn archetype:generate -DarchetypeArtifactId=maven-archetype-quickstart -DgroupId=com.mastertheboss -DartifactId=HibernateExample -Dversion=1.0.0
This will generate a basic Maven project with a pom.xml file. Let’s add now Hibernate and MySQL dependencies to it:
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.mastertheboss</groupId>
<artifactId>HibernateExample</artifactId>
<packaging>jar</packaging>
<version>1.0.0</version>
<name>HibernateExample</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.4.9.Final</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.48</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.4.0</version>
<configuration>
<mainClass>com.mastertheboss.App</mainClass>
<cleanupDaemonThreads>false</cleanupDaemonThreads>
</configuration>
</plugin>
</plugins>
</build>
</project>
Now you can fill your project with some basic classes; for this purposes we will use again the Department and Employee classes which are connected with a One to Many relationship.
Here’s the Department class:
package com.mastertheboss.domain;
import java.util.ArrayList;
import java.util.List;
import javax.persistence.*;
@Entity
@Table
public class Department {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@OneToMany(mappedBy="department",cascade=CascadeType.PERSIST)
private List<Employee> employees = new ArrayList<Employee>();
public Department() {
super();
}
public Department(String name) {
this.name = name;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
}
This is the Employee class:
package com.mastertheboss.domain;
import javax.persistence.*;
@Entity
@Table
public class Employee {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@ManyToOne
private Department department;
public Employee() {}
public Employee(String name, Department department) {
this.name = name;
this.department = department;
}
public Employee(String name) {
this.name = name;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Department getDepartment() {
return department;
}
public void setDepartment(Department department) {
this.department = department;
}
@Override
public String toString() {
return "Employee [id=" + id + ", name=" + name + ", department="
+ department.getName() + "]";
}
}
In order to create the Hibernate SessionFactory we will create an Utility class named HibernateUtil:
package com.mastertheboss.util;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static final SessionFactory sessionFactory = buildSessionFactory();
private static SessionFactory buildSessionFactory() {
try {
// Create the SessionFactory from hibernate.cfg.xml
return new Configuration().configure().buildSessionFactory();
} catch (Throwable ex) {
// Make sure you log the exception, as it might be swallowed
System.err.println("Initial SessionFactory creation failed." + ex);
throw new ExceptionInInitializerError(ex);
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
public static void shutdown() {
// Close caches and connection pools
getSessionFactory().close();
}
}
Fine. We will now add a test class which will test inserting Employees and Departments.
package com.mastertheboss.hibernate;
import java.util.List;
import com.mastertheboss.domain.Employee;
import com.mastertheboss.domain.Department;
import com.mastertheboss.util.*;
import org.hibernate.*;
public class HibernateTest {
public static void main(String[] args) {
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Department department = new Department("java");
session.save(department);
session.save(new Employee("Jakab Gipsz",department));
session.save(new Employee("Captain Nemo",department));
session.getTransaction().commit();
Query q = session.createQuery("From Employee ");
List<Employee> resultList = q.list();
System.out.println("num of employess:" + resultList.size());
for (Employee next : resultList) {
System.out.println("next employee: " + next);
}
}
}
Adding the Configuration
In order to work, this application requires an hibernate.cfg.xml file which needs to be placed into the resources/META-INF folder of your application. For the purpose of our example, we will suppose you have an active MySQL DB on localhost with a mysqldb database:
<?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="connection.url">jdbc:mysql://localhost:3306/mysqldb</property> <property name="connection.username">root</property> <property name="connection.password">my-secret-pw</property> <property name="connection.driver_class">com.mysql.jdbc.Driver</property> <property name="dialect">org.hibernate.dialect.MySQL5Dialect</property> <property name="show_sql">true</property> <property name="format_sql">true</property> <property name="hbm2ddl.auto">create</property> <!-- JDBC connection pool (use the built-in) --> <property name="connection.pool_size">1</property> <property name="current_session_context_class">thread</property> <mapping class="com.mastertheboss.domain.Employee" /> <mapping class="com.mastertheboss.domain.Department" /> </session-factory> </hibernate-configuration>
Please be aware that by using the property hbm2ddl.auto to create, the tables will be dropped and re-created each time that the application is deployed. Consider using another strategy if you are holding data in your tables like hbm2ddl.auto to validate – Thanks Adam Burley for pointing out this information.
Here’s how your project source should look like:
src
└── main
├── java
│ └── com
│ └── mastertheboss
│ ├── App.java
│ ├── domain
│ │ ├── Department.java
│ │ └── Employee.java
│ └── util
│ └── HibernateUtil.java
└── resources
└── hibernate.cfg.xml
That’s all! You can test your application with
mvn install exec:java
Hint
You don’t have MySQL installed to test this example? then you can use Docker to run it:
docker run -d -p 3306:3306 -e MYSQL_DATABASE="mysqldb" -e MYSQL_ROOT_PASSWORD=my-secret-pw mysql
Source code available here: https://github.com/fmarchioni/mastertheboss/tree/master/hibernate/HibernateExample
