Web编程学习六：使用Apache olingo将JPA数据库操作转化为RESTful Web Service

上次使用了Jersey来创建自己的RESTful web service，但是需要自己来创建每个方法，不是很方便。

今天来使用Apache olingo库来将JPA操作自动转化为RESTful service， Apache olingo是SAP捐给Apache的odata库。

下面来看看olingo和jersey相比，有多么的方便。

注意:在JPA转化RESTful的场景中，还需要使用Apache CXF包。

Olingo的主页：http://olingo.apache.org

开发环境是：Eclipse Juno, MySQL 5.5，olingo 1.2，EclipseLink 2.4, Tomcat 7

1.创建一个Dynamic Web Project，名字叫jpa2

2.加入JPA Facet，在lib中导入EclipseLink、MySql Connector、Olingo、Apache CXF包。

3.配置JPA的persistence.xml文件

<?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="jpa2" 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.数据对象Employee.java:

package sample;import javax.persistence.Basic;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;@Entitypublic class Employee {@Id@GeneratedValueprivate int id;@Basicprivate String firstName;@Basicprivate String lastName;public int getId() {return id;}public void setId(int 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;}}

5.创建一个继承ODataJPAServiceFactory的类

EmployeeServiceFactory

package sample;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;import org.apache.olingo.odata2.jpa.processor.api.ODataJPAContext;import org.apache.olingo.odata2.jpa.processor.api.ODataJPAServiceFactory;import org.apache.olingo.odata2.jpa.processor.api.exception.ODataJPARuntimeException;public class EmployeeServiceFactory extends ODataJPAServiceFactory {private static final String PERSISTENCE_UNIT_NAME = "jpa2";@Overridepublic ODataJPAContext initializeODataJPAContext()throws ODataJPARuntimeException {ODataJPAContext oDataJPAContext = this.getODataJPAContext();try {EntityManagerFactory emf = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);oDataJPAContext.setEntityManagerFactory(emf);oDataJPAContext.setPersistenceUnitName(PERSISTENCE_UNIT_NAME);return oDataJPAContext;} catch (Exception e) {throw new RuntimeException(e);}}}

6.创建web.xml，配置一下olingo

<?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>ODataServlet</servlet-name><servlet-class>org.apache.cxf.jaxrs.servlet.CXFNonSpringJaxrsServlet</servlet-class><init-param><param-name>javax.ws.rs.Application</param-name><param-value>org.apache.olingo.odata2.core.rest.app.ODataApplication</param-value></init-param><init-param><param-name>org.apache.olingo.odata2.service.factory</param-name><param-value>sample.EmployeeServiceFactory</param-value></init-param><load-on-startup>2</load-on-startup></servlet><servlet-mapping><servlet-name>ODataServlet</servlet-name><url-pattern>/Employee.svc/*</url-pattern></servlet-mapping></web-app>  

7.搞定，部署项目到Tomcat，往数据库表employee中输入几条测试数据：

8.用Chrome的PostMan来测试一下：

8.1查询全部对象

8.2查询单个对象

8.3创建一个对象

使用Post方法，向url: http://localhost:8080/jpa2/Employee.svc/Employees发送一个employee entry.

这里我用的RestClient:

创建成功后，返回201.

最后再查询一下，返回结果：

小结：从这个例子，可以看到olingo非常方便，只需要简单的配置，就可以自动将JPA全部自动转化为RESTful的Web Service了。