Dubbo 学习（3）— Dubbo 简单示例

先来写一个简洁的示例，此示例是后边所有源码的“鼻祖”。

Dubbo的设计目的

动态注册、发现服务，软负载均衡和服务降级。

描述服务依赖关系，描述整体服务架构。

统计服务负载，按需扩展容量。

简单实例

该实例参考官方实例，有所修改。

源码地址：https://gitee.com/liupeifeng3514/DubboLearning

整个项目结构：

dubbo-hello-init
.
├── dubbo-hello-api
│   ├── pom.xml
│   ├── src
│   │   ├── main
│   │   │   ├── java
│   │   │   │   └── com
│   │   │   │       └── tc
│   │   │   │           └── dubbo
│   │   │   │               └── hello
│   │   │   │                   └── HelloService.java
│   │   │   └── resources
│   │   └── test
│   │       └── java
│   └── target
│
├── dubbo-hello-consumer
│   ├── pom.xml
│   ├── src
│   │   ├── main
│   │   │   ├── java
│   │   │   │   └── com
│   │   │   │       └── tc
│   │   │   │           └── dubbo
│   │   │   │               └── hello
│   │   │   │                   └── consumer
│   │   │   │                       └── Consumer.java
│   │   │   └── resources
│   │   │       ├── META-INF
│   │   │       │   └── spring
│   │   │       │       └── dubbo-hello-consumer.xml
│   │   │       ├── dubbo.properties
│   │   │       └── log4j.properties
│   │   └── test
│   │       └── java
│   └── target
│
├── dubbo-hello-provider
│   ├── pom.xml
│   ├── src
│   │   ├── main
│   │   │   ├── java
│   │   │   │   └── com
│   │   │   │       └── tc
│   │   │   │           └── dubbo
│   │   │   │               └── hello
│   │   │   │                   └── provider
│   │   │   │                       ├── HelloServiceImpl.java
│   │   │   │                       └── Provider.java
│   │   │   └── resources
│   │   │       ├── META-INF
│   │   │       │   └── spring
│   │   │       │       └── dubbo-hello-provider.xml
│   │   │       ├── dubbo.properties
│   │   │       └── log4j.properties
│   │   └── test
│   │       └── java
│   └── target
└── pom.xml

整个项目分为三个模块，dubbo-hello-api、dubbo-hello-provider和dubbo-hello-consumer。以下是整个dubbo-hello-init工程的pom内容：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion>

<groupId>com.lpf</groupId>
<artifactId>dubbo-hello</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>pom</packaging>

<name>父工程</name>
<description>父工程</description>

<properties>
<skip_maven_deploy>false</skip_maven_deploy>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>

<modules>
<module>dubbo-hello-api</module>
<module>dubbo-hello-provider</module>
<module>dubbo-hello-consumer</module>
</modules>
</project>

公共API定义

一般Provider和Consumer共享的接口应该单独一个包进行定义，方便双方的共享。这里新建了模块dubbo-hello-api来定义公共接口。其pom文件为基本配置，无特殊性，简单定义接口HelloService如下：

package com.lpf.dubbo.hello;

public interface HelloService {
String sayHello(String name);
}

Provider实现

服务提供者模块dubbo-hello-provider的pom文件内容如下：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion>

<parent>
<groupId>com.lpf</groupId>
<artifactId>dubbo-hello</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>

<artifactId>dubbo-hello-provider</artifactId>
<packaging>jar</packaging>
<name>提供者</name>
<description>提供者示例</description>

<properties>
<skip_maven_deploy>false</skip_maven_deploy>
</properties>

<dependencies>
<dependency>
<groupId>com.lpf</groupId>
<artifactId>dubbo-hello-api</artifactId>
<version>${project.parent.version}</version>
</dependency>

<dependency>
<groupId>com.alibaba</groupId>
<artifactId>dubbo</artifactId>
<version>2.6.1</version>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.3</version>
<configuration>
<appendAssemblyId>false</appendAssemblyId>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>com.lpf.dubbo.hello.provider.Provider</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>assembly</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>

</project>

其中声明了对com.lpf:dubbo-hello-api接口的依赖，还有对com.alibaba:dubbo的依赖。插件plugin声明了采用加入依赖的打包方式，这样方便直接运行。

在文件dubbo-hello-provider.xml中声明了要暴露的服务：

<?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-4.3.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="hello-provider" />

<!-- use multicast registry center to export service -->
<dubbo:registry address="multicast://224.5.6.7:1234" />

<!-- use dubbo protocol to export service on port 20880 -->
<dubbo:protocol name="dubbo" port="20880" />

<!-- service implementation, as same as regular local bean -->
<bean id="helloService" class="com.lpf.dubbo.hello.provider.HelloServiceImpl" />

<!-- declare the service interface to be exported -->
<dubbo:service interface="com.lpf.dubbo.hello.HelloService" ref="helloService" />

</beans>

其中说明了注册方式为multicast，也即利用广播，无注册中心的方式。同时声明了协议和端口号。

暴露的服务HelloServiceImpl实现如下：

package com.lpf.dubbo.hello.provider;

import com.alibaba.dubbo.rpc.RpcContext;
import com.lpf.dubbo.hello.HelloService;

import java.text.SimpleDateFormat;
import java.util.Date;

public class HelloServiceImpl implements HelloService {
public String sayHello(String name) {
System.out.println("[" + new SimpleDateFormat("HH:mm:ss").format(new Date()) + "] Hello " + name + ", request from consumer: " + RpcContext.getContext().getRemoteAddress());
return "Hello " + name + ", response form provider: " + RpcContext.getContext().getLocalAddress();
}
}

入口类Provider的实现如下：

package com.lpf.dubbo.hello.provider;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Provider {

public static void main(String[] args) throws Exception {
// Prevent to get IPV6 address,this way only work in debug mode
// But you can pass use -Djava.net.preferIPv4Stack=true,then it work well
// whether in debug mode or not
System.setProperty("java.net.preferIPv4Stack", "true");
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "META-INF/spring/dubbo-hello-provider.xml" });
context.start();

System.in.read(); // press any key to exit
}
}

Consumer实现

其pom文件和Provider类似：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion>

<parent>
<groupId>com.lpf</groupId>
<artifactId>dubbo-hello</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>

<artifactId>dubbo-hello-consumer</artifactId>
<packaging>jar</packaging>

<name>消费者</name>
<description>消费者示例</description>

<dependencies>
<dependency>
<groupId>com.lpf</groupId>
<artifactId>dubbo-hello-api</artifactId>
<version>${project.parent.version}</version>
</dependency>

<dependency>
<groupId>com.alibaba</groupId>
<artifactId>dubbo</artifactId>
<version>2.6.1</version>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.3</version>
<configuration>
<appendAssemblyId>false</appendAssemblyId>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>com.tc.dubbo.hello.consumer.Consumer</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>assembly</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>

</project>

其dubbo-hello-consumer.xml配置如下，声明了对服务的引用。

<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-4.3.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="hello-consumer" />

<!-- use multicast registry center to discover service -->
<dubbo:registry address="multicast://224.5.6.7:1234" />

<!-- generate proxy for the remote service, then demoService can be used in the same way as the local regular interface -->
<dubbo:reference id="helloService" check="false" interface="com.lpf.dubbo.hello.HelloService" />

</beans>

入口类Consumer实现如下：

package com.lpf.dubbo.hello.consumer;

import com.lpf.dubbo.hello.HelloService;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Consumer {

public static void main(String[] args) {
// Prevent to get IPV6 address,this way only work in debug mode
// But you can pass use -Djava.net.preferIPv4Stack=true,then it work well
// whether in debug mode or not
System.setProperty("java.net.preferIPv4Stack", "true");
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "META-INF/spring/dubbo-hello-consumer.xml" });
context.start();
HelloService helloService = (HelloService) context.getBean("helloService"); // get remote service proxy

while (true) {
try {
Thread.sleep(1000);
String hello = helloService.sayHello("world"); // call remote method
System.out.println(hello); // get result

} catch (Throwable throwable) {
throwable.printStackTrace();
}
}
}
}

附：实验过程中的问题

com.alibaba.dubbo.rpc.RpcException: Failed to invoke the method 错误处理

参考篇博文：https://blog.csdn.net/wjb_2016/article/details/51084916