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;

@Entity
public class Employee {
@Id
@GeneratedValue
private int id;

@Basic
private String firstName;

@Basic
private 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";

@Override
public 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。