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="" xmlns:xsi=""xsi:schemaLocation=" 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="" xmlns="" xmlns:web="" xsi:schemaLocation=" 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;@WebListenerpublic class LocalEntityManagerFactory implements ServletContextListener {private static EntityManagerFactory emf;@Overridepublic void contextInitialized(ServletContextEvent event) {emf = Persistence.createEntityManagerFactory("EmployeePU");System.out.println("ServletContextListener started");}@Overridepublic 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。
下午某时，天气晴，我在某地，想念你。
