JPA (Java Persistence API) in Eclipse
Introduction
Let's make a JPA sample program in Eclipse. Modify MVC program and use JPA to get data from Postgre SQL DB. Create an Emplyee table in advance. (See: Install Postgre SQL)
Development environment
Windows 10 Pro 1709(16299.192) Eclipse pleiades-4.7.3 java 1.8.0_162 PostgreSQL 10.4 Released!
procedure
-
- Download PostgreSQL JDBC Driver
-
Copy to WEB-INF \ lib of project
-
- Create a connection to Postgres SQL
-
Convert to JPA project
-
Source code changes
-
Operation check
1. 1. Download PostgreSQL JDBC Driver
URL
https://jdbc.postgresql.org/download.html
1. Click "PostgreSQL JDBC 4.2 Driver, 42.2.2"
2. Copy to WEB-INF \ lib of project
3. 3. Create a connection to Postgres SQL
1. Select "Window"-> "View View"-> "Other" menu
2. Select "Data Management" "Data Source Explorer" and click "Open"
3. Click "New" on the right menu on "Data Source Connection"
4. Select Postgres SQL and click Next
5. Enter "Database", "URL", "Username" and "Password" and click "Test Connection".
6. Confirm "Ping completed successfully" and click the "OK" button.
7. Click the "Finish" button
8. You can see the table created in Install Postgre SQL
4. Convert to JPA project
1. Select Right Menu-> Configuration-> Convert to JPA Project on the project
2. Click "Next"
3. Select "EclipseLink 2.5.2" and click "Next"
4. Check "Accept the terms of this license" and click "Finish"
5. Select the "New PostgreSQL" connection, check "Build Path", "Override Default Catalog from Connection", "Override Default Schema from Connection", and click "Finish".
6. Select Right Menu-> JPA Tools-> Generate Entity from Table on Project
7. Check the "employee" table and click "Finish"
5. Source code changes
1. Add @NamedQuery of findById to Employee Entity
Change before
@Entity
@NamedQuery(name="Employee.findAll", query="SELECT e FROM Employee e")
public class Employee implements Serializable {
After change
@Entity
@NamedQueries({
@NamedQuery(name="Employee.findAll", query="SELECT e FROM Employee e"),
@NamedQuery(name = "Employee.findById", query = "SELECT e from Employee e where e.id = :id")
})
public class Employee implements Serializable {
2. Changed to get EmployeeServlet from DB
After change
package emp;
import java.io.IOException;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import model.Employee;
/**
* Servlet implementation class EmployeeServlet
*/
@WebServlet(name = "EmpList", urlPatterns = { "/EmpList" })
public class EmployeeServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public EmployeeServlet() {
super();
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("SampleMVC2");
EntityManager entityManager = emf.createEntityManager();
List<Employee> employeeList = entityManager
.createNamedQuery("Employee.findAll", Employee.class)
.getResultList();
entityManager.close();
emf.close();
//Pass Model data to View
request.setAttribute("employeeList", employeeList);
//Show View
this.getServletContext()
.getRequestDispatcher("/employeeList.jsp")
.forward(request, response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("SampleMVC2");
EntityManager entityManager = emf.createEntityManager();
List<Employee> employeeList;
String id = request.getParameter("id");
if (id.isEmpty()) {
employeeList = entityManager
.createNamedQuery("Employee.findAll", Employee.class)
.getResultList();
}
else {
employeeList = entityManager
.createNamedQuery("Employee.findById", Employee.class)
.setParameter("id", id)
.getResultList();
}
entityManager.close();
emf.close();
//Pass Model data to View
request.setAttribute("employeeList", employeeList);
//Show View
this.getServletContext()
.getRequestDispatcher("/employeeList.jsp")
.forward(request, response);
}
}
3. Right menu on Employee Bean-> Select "Delete"
4. Select "OK"
5. Change "persistence.xml"
Change before
<?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="SampleMVC">
<class>model.Employee</class>
</persistence-unit>
</persistence>
After change (DB connection information added)
<?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="SampleMVC2">
<class>model.Employee</class>
<properties>
<property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" /> <!-- DB Driver -->
<property name="javax.persistence.jdbc.url" value="jdbc:postgresql://localhost/postgres" /> <!-- BD Mane -->
<property name="javax.persistence.jdbc.user" value="postgres" /> <!-- DB User -->
<property name="javax.persistence.jdbc.password" value="dev" /> <!-- DB Password -->
</properties>
</persistence-unit>
</persistence>
6. Operation check
[Refer to "MVC with Eclipse." Operation check](https://qiita.com/0ashina0/items/7c378823905949b301af#4-%E5%8B%95%E4%BD%9C%E7%A2%BA%E8% AA% 8D)
in conclusion
--The annotation @PersistenceContext can be added to EntityManager only when transaction management (container management) is performed. Otherwise @PersistenceContext is ignored.
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