HelloWorld JPA application

In this tutorial we will learn how to create a simple Hello World JPA application to be deployed on WildFly or any Java EE container.

Create the Maven project

We will need a Maven archetype to bootstrap a Web application project. You can use one simple like the following one:

mvn -DarchetypeGroupId=org.codehaus.mojo.archetypes \
-DarchetypeArtifactId=webapp-javaee7 \
-DgroupId=com.mastertheboss -DartifactId=jpa-basic \
-Dversion=1.1 -Dpackage=com.mastertheboss \
-Darchetype.interactive=false --batch-mode --update-snapshots \
archetype:generate

Now Let’s write our simple Entity class that we will persist in the Database:

package com.mastertheboss.model;

import javax.enterprise.event.Event;
import javax.inject.Inject;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.PostRemove;

@Entity
public class SimpleProperty {


	@Id
	@Column(name="id")
	private String key;

	private String value;

	public String getKey() {
		return key;
	}

	public void setKey(String key) {
		this.key = key;
	}

	@Override
	public String toString() {
		return "SimpleProperty [key=" + key + ", value=" + value + "]";
	}

	public String getValue() {
		return value;
	}

	public void setValue(String value) {
		this.value = value;
	}



}

Now, in order to store our Entity in a transactional way, we need an EJB:

package com.mastertheboss.ejb;

import java.util.List;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import com.mastertheboss.model.SimpleProperty;



@Stateless

public class  ServiceBean   {

	@PersistenceContext
	private EntityManager em;

	public void put(SimpleProperty p){

		em.persist(p);
	}

	public void delete(SimpleProperty p){

		Query query = em.createQuery("delete FROM SimpleProperty p where p.key='"+p.getKey()+"'");

		query.executeUpdate();

	}

	public List<SimpleProperty> findAll(){

		Query query = em.createQuery("FROM SimpleProperty");

		List <SimpleProperty> list = query.getResultList();
		return list;

	}

	public SimpleProperty findById(String id){

		SimpleProperty p = em.find(SimpleProperty.class, id);
		return p;

	}

}

Finally, we need a front-end for our application. To keep it pretty simple, a basic REST Endpoint will be added:

package com.mastertheboss.rest;

import java.util.HashMap;
import java.util.List;
import java.util.Map;


import javax.enterprise.context.RequestScoped;
import javax.inject.Inject;
import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

import com.mastertheboss.model.SimpleProperty;
import com.mastertheboss.ejb.ServiceBean;

/**
 * JAX-RS Example
 * <p/>
 * This class produces a RESTful service to read/write the contents of the members table.
 */
@Path("/action")
@RequestScoped
public class RestService {

	@Inject
	private ServiceBean ejb;

	@GET
	@Produces(MediaType.APPLICATION_JSON)
	public List<SimpleProperty> listAllMembers() {
		return ejb.findAll();
	}

	@GET
	@Path("/id/{id}")
	@Produces(MediaType.APPLICATION_JSON)
	public SimpleProperty findById(@PathParam("id") String id) {

		SimpleProperty p = ejb.findById(id);
		if (p == null) {
			throw new WebApplicationException(Response.Status.NOT_FOUND);
		}
		return p;
	}

	@POST
	@Consumes(MediaType.APPLICATION_JSON)
	@Produces(MediaType.APPLICATION_JSON)
	public Response createMember(SimpleProperty member) {

		Response.ResponseBuilder builder = null;

		try {

			ejb.put(member);
			// Create an "ok" response
			builder = Response.ok("Saved!");

		} catch (Exception e) {
			// Handle generic exceptions
			Map<String, String> responseObj = new HashMap<>();
			responseObj.put("error", e.getMessage());
			builder = Response.status(Response.Status.BAD_REQUEST).entity(responseObj);
		}

		return builder.build();
	}


}

As you can see, the above REST endpoint has some basic methods for creating and querying our Entity objects, returning a JSON view of it.

In order to get it working, we need a REST Activator class:

package com.mastertheboss.rest;

import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;

@ApplicationPath("/rest")
public class RestActivator extends Application {
	
}

Done with the code, we will add a persistence.xml file to declare the mapping for our PersistenceContext objects:

<?xml version="1.0" encoding="UTF-8"?>

<persistence version="2.1"
             xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="
        http://xmlns.jcp.org/xml/ns/persistence
        http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="primary">
        <jta-data-source>java:jboss/datasources/ExampleDS</jta-data-source>
        <properties>
            <!-- Properties for Hibernate -->
            <property name="hibernate.hbm2ddl.auto" value="create-drop" />
            <property name="hibernate.show_sql" value="false" />
        </properties>
    </persistence-unit>
</persistence>

As you can see, we rely on the default Datasource which ships with WildFly. Here is the final project tree structure:

src
└── main
    ├── java
    │   └── com
    │       └── mastertheboss
    │           ├── ejb
    │           │   └── ServiceBean.java
    │           ├── model
    │           │   └── SimpleProperty.java
    │           └── rest
    │               ├── RestActivator.java
    │               └── RestService.java
    ├── resources
    │   └── META-INF
    │       └── persistence.xml
    └── webapp
        ├── index.html
        └── WEB-INF
            └── beans.xml

Now compile the project:

$ mvn clean install

The deploy it on WildFly. We can start by adding some data using a POST with cURL:

$ curl --header "Content-Type: application/json" \
  --request POST \
  --data '{"key":"xyz","value":"xyz"}' \
  http://localhost:8080/jpa-basic/rest/action

We can check that data was inserted with:

$ curl http://localhost:8080/jpa-basic/rest/action

[{"key":"xyz","value":"xyz"}]

Much the same, we can query by id. It will return the same id:

$ curl http://localhost:8080/jpa-basic/rest/action/id/xyz

[{"key":"xyz","value":"xyz"}]

That’s all! Enjoy your first JPA application example on WildFly!

You can find the source code for this JPA application on: https://github.com/fmarchioni/mastertheboss/tree/master/javaee/jpa-basic