Web编程学习五: 使用Jersey和JPA来创建RESTful WebService

在上一个练习学习了如何使用Jersey，以及JAXB来创建RESTful的web service。

现在我来结合后台数据库对其做升级，也就是通过Jersey创建用来修改后台数据库的RESTful web service。

开发环境：

Eclipse Juno， 数据库MySQL 5.5， Jersey 1.18，EclipseLink 2.4, JAVA 1.6, 应用服务器Tomcat 7。

1.创建一个叫做jersey3的Dynamic Web Project。添加JPA的facet。

2.导入Jersey包，导入EclipseLink包，导入MySQL的connect包。

3.开发数据库对象，配置JPA。

数据对象Employee类：

package sample;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
@Entity
@Table(name = "employee")
public class Employee {
	@Id
	@Column(name = "userId")
	private Long id;
	@Column(name = "firstName")
	private String firstName;
	@Column(name = "lastName")
	private String lastName;

	public long getId() {
		return id;
	}

	public void setId(long id) {
		this.id = id;
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
}

persistence.xml:

<?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="EmployeePU" transaction-type="RESOURCE_LOCAL">
		<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
		<class>sample.Employee</class>
		<properties>
			<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:8889/test" />
			<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
			<property name="javax.persistence.jdbc.user" value="root" />
			<property name="javax.persistence.jdbc.password" value="root" />
		</properties>
	</persistence-unit>
</persistence>

4.配置Jersey，编写代码来实现RESTful web service。

创建web.xml:

<?xml version="1.0" encoding="UTF-8"?>    
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">    
  <display-name>RestProjectTest</display-name>    
 <servlet>    
    <servlet-name>Jersey REST Service</servlet-name>    
    <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>    
    <init-param>    
      <param-name>com.sun.jersey.config.property.packages</param-name>    
      <param-value>sample</param-value>    
    </init-param>    
          <init-param>    
        <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>    
        <param-value>true</param-value>    
    </init-param>        
    <load-on-startup>1</load-on-startup>    
  </servlet>    
  <servlet-mapping>    
    <servlet-name>Jersey REST Service</servlet-name>    
    <url-pattern>/*</url-pattern>    
  </servlet-mapping>    
<listener>  
        <listener-class>sample.LocalEntityManagerFactory</listener-class>  
    </listener></span>  
</web-app>    

注意添加了一个监听器LocalEntityManagerFactory，实现了ServletContextListener类，它可以在应用启动和关闭的时候后自动调用。

可以来管理我们的EntityManager。

package sample;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class LocalEntityManagerFactory implements ServletContextListener {
	private static EntityManagerFactory emf;

	@Override
	public void contextInitialized(ServletContextEvent event) {
		emf = Persistence.createEntityManagerFactory("EmployeePU");
		
		System.out.println("ServletContextListener started");
	}

	@Override
	public void contextDestroyed(ServletContextEvent event) {
		emf.close();
		System.out.println("ServletContextListener destroyed");
	}

	public static EntityManager createEntityManager() {
		if (emf == null) {
			throw new IllegalStateException("Context is not initialized yet.");
		}
		return emf.createEntityManager();
	}
}

开发好JPA相关的持久化功能后，就可以来实现RESTful service了，代码：

package sample;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

@Path("/employee")
public class EmployeeController {
	@GET
	@Produces({ MediaType.TEXT_XML })
	@Path("{id}")
	public Employee read(@PathParam("id") long id) {
		long start = System.currentTimeMillis();
		System.out.println("EmployeeController.read() started");
		EntityManager em = LocalEntityManagerFactory.createEntityManager();
		try {
			return em.find(Employee.class, id);
		} finally {
			em.close();
			System.out.println("Getting data took "
					+ (System.currentTimeMillis() - start) + "ms.");
		}
	}

	@GET
	@Produces({ MediaType.TEXT_XML })
	public List<Employee> read() {
		long start = System.currentTimeMillis();
		System.out.println("EmployeeController.read() started");
		EntityManager em = LocalEntityManagerFactory.createEntityManager();
		try {
			Query q = em.createQuery("SELECT e FROM Employee e");
			List<Employee> result = q.getResultList();
			return result;
		} finally {
			em.close();
			System.out.println("Getting data took "
					+ (System.currentTimeMillis() - start) + "ms.");
		}
	}

}

这里实现了两个GET接口，一个按照ID返回单个Employee对象，另一个返回全部Employee对象。

5.准备几条测试数据，插入到数据库表中。

6.测试，这里我用的Chrome浏览器插件的POSTMAN来测试。

6.1测试1，单个查询

输入url: http://localhost:8080/jersey3/employee/{id}

6.2测试2,查询全部数据

输入URL: http://localhost:8080/jersey3/employee/

小结：

这个例子很简单，配置好JPA和Jersey后，主要就是在Jersey的实现方法中把数据的CRUD需求交给JPA的Entity Manager来完成就可以了。