tanszek:oktatas:jpa [Miskolci Egyetem Informatikai Intézet]

JPA Example

Create a dynamic web project (name should be “JPA”) and follow these steps::

1.) Create a persistence.xml file in folder src/META-INF with the following content:

  <?xml version="1.0" encoding="UTF-8"?>
  <persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  	<persistence-unit name="customers">
  	<jta-data-source>java:jboss/datasources/ExampleDS</jta-data-source>
  		<properties>
  			<property name="hibernate.hbm2ddl.auto" value="create-drop" />
  			<property name="showSql" value="true"/>
  			<property name="hibernate.dialect"
  					value="org.hibernate.dialect.MySQLDialect" />
  		</properties>
  	</persistence-unit>
  </persistence>

2.) Create org.me.CustomerManager class:

  package org.me;
  
  import java.util.List;
  import javax.ejb.EJB;
  import javax.ejb.Stateful;
  import javax.ejb.Stateless;
  import javax.persistence.EntityManager;
  import javax.persistence.PersistenceContext;
  import javax.persistence.Query;
  
  @Stateless
  public class CustomerManager {
  	@PersistenceContext(unitName = "customers")
  	EntityManager em;
  
  	public void createCustomer(String name, String address) {
  		Customer customer = new Customer(name, address);
  	        em.persist(customer);  
  	}
  
  	public List<Customer> listCustomers() {
  		String q = "SELECT b from " + Customer.class.getName() + " b";
  		Query query = em.createQuery(q);
  		return query.getResultList();
  	}
  }

3. Create a class org.me.Customer

  package org.me;
  
  import java.io.Serializable;
  import javax.persistence.Entity;
  import javax.persistence.Id;
  
  @Entity(name = "customer")
  public class Customer implements Serializable {
  	@Id
  	private String name;
  	private String address;
  	
  	public Customer() {
  	}
  	
  	public Customer(String name, String address) {
  		this.name = name;
  		this.address = address;
  	}
  	
  	public String getName() {
  		return name;
  	}
  	public void setName(String name) {
  		this.name = name;
  	}
  	public String getAddress() {
  		return address;
  	}
  	public void setAddress(String address) {
  		this.address = address;
  	}
  }

4.) Create org.me.MyServlet class

  package org.me;
  
  import java.io.IOException;
  import java.io.PrintWriter;
  import java.util.List;
  
  import javax.ejb.EJB;
  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  @WebServlet("/MyServlet")
  public class MyServlet extends HttpServlet {
  
      @EJB
      private CustomerManager cm;
  
      public MyServlet() {
          super();
      }
  
  	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  		String method = request.getParameter("method");
  		String name = request.getParameter("name");
  		String address = request.getParameter("address");
  
  		PrintWriter writer = response.getWriter();
  	        writer.print("<html><body>");
  
  		if(method.equalsIgnoreCase("create")) {
  		    cm.createCustomer(name, address);
  		    writer.print("result = OK, saved");
  		} else if(method.equalsIgnoreCase("list")) {
  			List<Customer> persons = cm.listCustomers();
  			for (Customer customer : persons) {
  			    writer.print("customer.name=" + customer.getName() + " address=" + customer.getAddress() + "</br>");				
  			}	
  		}
  	        writer.print("</body> </html>");
  
  		writer.flush();
  		writer.close();
  	}
  }

5.) How to try it out?

http://localhost:8080/JPA/MyServlet?method=create&name=john1&address=miskolc

http://localhost:8080/JPA/MyServlet?method=create&name=john2&address=miskolc

http://localhost:8080/JPA/MyServlet?method=create&name=john3&address=miskolc

List saved instances:

http://localhost:8080/JPA/MyServlet?method=list&name=john1&address=miskolc

Exercises

Download this tool: h2console.zip. Extract to ..\jbdevstudio\runtimes\jboss-eap\standalone\deployments\ and launch it: http://localhost:8080/h2console/
- Connection string: jdbc:h2:mem:test;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE
- User/Pass: sa/sa
- Explore tables and menu items
Create a HTML form (index.html) to manipulate customers

one possible solution:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
	<form action="MyServlet">
	 Name: <input type="text" name="name"> <br>
	 Address: <input type="text" name="address"> <br>
	 <input type="submit" name="method" value="create">
	 <input type="submit" name="method" value="list">
	 <input type="submit" name="method" value="delete">
	</form>
</body>
</html>

Extend functionality with deleting instances. Query language tutorial can be found here: http://docs.oracle.com/javaee/6/tutorial/doc/bnbtl.html#bnbtm

One possible solution:

    public int delete(String name) {
      String q = "DELETE from " + Customer.class.getName()
            + " b WHERE b.name = '" + name + "'";
      Query query = em.createQuery(q);
      return query.executeUpdate();
    }