如何使用Dubbo开发REST接口

从阿里重新维护Dubbo开始，这个开源项目突然变得特别活跃。
新推出的2.6.0版本更合并了当当网Dubbox的部分特性，现已支持开发Rest接口。下面是笔者的尝试，请参考。

---

提供者

1、定义接口
ServiceFacade.java

public interface ServiceFacade {
    String hello();
}

2、实现接口
ServiceImpl.java

@Path("demo")
public class ServiceImpl implements ServiceFacade {

    @Override
    @Path("hello")
    @GET
    public String hello() {
        return "Hello World! ";
    }
}

REST风格基于标准的Java REST API——JAX-RS 2.0实现，访问URL为：
http://ip:port/demo/hello
这里的@Path、@GET 来自jaxrs-api.jar，dubbo-2.6.0没有自带，需要自己依赖：

<dependency>
	<groupId>org.jboss.resteasy</groupId>
	<artifactId>resteasy-client</artifactId>
	<version>3.0.12.Final</version>
</dependency>

3、暴露接口
provider.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"
       xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
       http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd">

    <!-- provider's application name, used for tracing dependency relationship -->
    <dubbo:application name="demo-provider"/>

    <!-- use multicast registry center to export service -->
    <dubbo:registry address="zookeeper://127.0.0.1:2181"/>

    <!-- use dubbo protocol to export service on port 20880 -->
    <dubbo:protocol name="dubbo" port="2080"/>
    <dubbo:protocol name="rest" port="8080" server="tomcat"/>

    <bean id="demoService" class="com.free.dubbo.demo.provider.ServiceImpl"/>
    <!-- declare the service interface to be exported -->
    <dubbo:service interface="com.free.dubbo.demo.provider.ServiceFacade" ref="demoService" protocol="dubbo,rest"/>
</beans>

上面server笔者使用了tomcat，这里是可选的（netty、jetty、servlet等），因此也需要添加下面的依赖：

<!--for rest protocal-->
<dependency>
	<groupId>org.apache.tomcat.embed</groupId>
	<artifactId>tomcat-embed-core</artifactId>
	<version>8.0.11</version>
</dependency>
<dependency>
	<groupId>org.apache.tomcat.embed</groupId>
	<artifactId>tomcat-embed-logging-juli</artifactId>
	<version>8.0.11</version>
</dependency>
<dependency>
	<groupId>javax.validation</groupId>
	<artifactId>validation-api</artifactId>
	<version>1.1.0.Final</version>
</dependency>

4、启动提供者
Provider.java

public class Provider {
    public static void main(String[] args) throws Exception{
        FileSystemXmlApplicationContext context = new FileSystemXmlApplicationContext("classpath:provider.xml");
        context.start();
        // 阻塞
        System.in.read();
    }
}

消费者

1、定义dubbo接口引用
consumer.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"
       xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
       http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd">

    <!-- consumer's application name, used for tracing dependency relationship (not a matching criterion),
    don't set it same as provider -->
    <dubbo:application name="demo-consumer"/>

    <!-- use multicast registry center to discover service -->
    <dubbo:registry address="zookeeper://127.0.0.1:2181"/>

    <!-- generate proxy for the remote service, then demoService can be used in the same way as the
    local regular interface -->
    <dubbo:reference id="demoService" check="true" interface="com.free.dubbo.demo.provider.ServiceFacade"/>
</beans>

这里只是定义了dubbo协议引用，rest接口像普通url访问就可以了。

2、调用接口
ConsumerDemo.java

public class ConsumerDemo {
    public static void main(String[] args) throws Exception{
        FileSystemXmlApplicationContext context = new FileSystemXmlApplicationContext("classpath:consumer.xml");
        context.start();

        // Test dubbo protocal
        ServiceFacade serviceDemo = context.getBean(ServiceFacade.class);
        System.out.println("Dubbo result: " + serviceDemo.hello());

        // Test rest protocal
        HttpClient client = HttpClientBuilder.create()
                .build();
        RequestConfig config = RequestConfig.custom()
                .setConnectTimeout(3000)
                .setSocketTimeout(3000)
                .build();
        HttpGet httpGet = new HttpGet("http://localhost:8080/demo/hello");
        httpGet.setConfig(config);

        HttpResponse httpResponse = client.execute(httpGet);
        int statusCode = httpResponse.getStatusLine()
                .getStatusCode();

        if (200 != statusCode) {
            System.out.println("WARN: Response code is" + statusCode);
        }
        String response = EntityUtils.toString(httpResponse.getEntity(), Charset.forName("UTF-8"));

        Assert.notNull(response, "Return null when invoke rest interface. ");
        System.out.println("Rest result: " + response);
    }

}

输出：

Dubbo result: Hello World! 
Rest result: Hello World! 

Process finished with exit code 0

如果想了解更多，可以参考
1、在Dubbo中开发REST风格的远程调用：
https://dangdangdotcom.github.io/dubbox/rest.html
2、Dubbo主页：http://dubbo.io