POJO 序列化兼容模式

本教程将从头开始构建一个简单的项目，演示如何基于 POJO 使用 Dubbo Triple，并在应用程序不改变现有接口定义的情况下升级到 Triple 协议。**在这种模式下，Triple 的使用方式与 Dubbo 协议相同。**

有关特定用例，请参考：[dubbo-samples-triple/pojo](https://github.com/apache/dubbo-samples/tree/master/3-extensions/protocol/dubbo-samples-triple/src/main/java /org/apache/dubbo/sample/tri/pojo);

前提条件

• JDK 版本 >= 8
• 已安装 Maven
• 已安装并启动 Zookeeper

创建项目

1. 首先创建一个空的 Maven 项目

   $ mvn archetype:generate \
       -DgroupId=org.apache.dubbo \
       -DartifactId=tri-pojo-demo\
       -DarchetypeArtifactId=maven-archetype-quickstart\
       -DarchetypeVersion=1.4 \
       -DarchetypeGroupId=org.apache.maven.archetypes \
       -Dversion=1.0-SNAPSHOT
   

2. 切换到项目目录

   $ cd tri-pojo-demo
   

3. 在 pom.xml 中设置 JDK 版本，添加 Dubbo 依赖项和插件

   <properties>
       <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>
   
   <dependencies>
      <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.13</version>
          <scope>test</scope>
      </dependency>
      <dependency>
          <groupId>org.apache.dubbo</groupId>
          <artifactId>dubbo</artifactId>
          <version>3.0.8</version>
      </dependency>
      <dependency>
       <groupId>org.apache.dubbo</groupId>
       <artifactId>dubbo-dependencies-zookeeper-curator5</artifactId>
       <type>pom</type>
       <version>3.0.8</version>
      </dependency>
       <dependency>
           <groupId>com.google.protobuf</groupId>
           <artifactId>protobuf-java</artifactId>
           <version>3.19.4</version>
       </dependency>
   </dependencies>
   

4. 添加接口定义 src/main/java/org/apache/dubbo/Greeter.java

   package org.apache.dubbo;
   
   public interface Greeter {
      String sayHello(String name);
   }
   

5. 添加服务器端接口实现 src/main/java/org/apache/dubbo/GreeterImpl.java

   package org.apache.dubbo;
   
   public class GreeterImpl implements Greeter {
      @Override
      public String sayHello(String name) {
         return "Hello," + name + "!";
      }
   }
   

6. 添加服务器启动类 src/main/java/org/apache/dubbo/MyDubboServer.java

   package org.apache.dubbo;
   
   import org.apache.dubbo.common.constants.CommonConstants;
   import org.apache.dubbo.config.ApplicationConfig;
   import org.apache.dubbo.config.ProtocolConfig;
   import org.apache.dubbo.config.RegistryConfig;
   import org.apache.dubbo.config.ServiceConfig;
   import org.apache.dubbo.config.bootstrap.DubboBootstrap;
   
   import java.io.IOException;
   
   public class MyDubboServer {
   
      public static void main(String[] args) throws IOException {
          ServiceConfig<Greeter> service = new ServiceConfig<>();
          service.setInterface(Greeter.class);
          service.setRef(new GreeterImpl());
   
          DubboBootstrap bootstrap = DubboBootstrap. getInstance();
          bootstrap. application(new ApplicationConfig("tri-pojo-server"))
                  .registry(new RegistryConfig("zookeeper://127.0.0.1:2181"))
                  .protocol(new ProtocolConfig(CommonConstants.TRIPLE, 50051))
                  .service(service)
                  .start();
          System.out.println("Dubbo triple pojo server started");
          System.in.read();
      }
   }
   

7. 添加客户端启动类 src/main/java/org/apache/dubbo/MyDubboClient.java

   package org.apache.dubbo;
   
   import org.apache.dubbo.common.constants.CommonConstants;
   import org.apache.dubbo.config.ApplicationConfig;
   import org.apache.dubbo.config.ReferenceConfig;
   import org.apache.dubbo.config.RegistryConfig;
   import org.apache.dubbo.config.bootstrap.DubboBootstrap;
   
   public class MyDubboClient {
      public static void main(String[] args) {
         DubboBootstrap bootstrap = DubboBootstrap. getInstance();
         ReferenceConfig<Greeter> ref = new ReferenceConfig<>();
         ref. setInterface(Greeter. class);
         ref.setProtocol(CommonConstants.TRIPLE);
         ref. setTimeout(3000);
         bootstrap. application(new ApplicationConfig("tri-pojo-client"))
          .registry(new RegistryConfig("zookeeper://127.0.0.1:2181"))
          .reference(ref)
          .start();
   
         Greeter greeter = ref. get();
         String reply = greeter. sayHello("pojo");
         System.out.println("Received reply:" + reply);
       }
   }
   

8. 编译代码

   $ mvn clean install
   

9. 启动服务器

   $ mvn org.codehaus.mojo:exec-maven-plugin:3.0.0:java -Dexec.mainClass="org.apache.dubbo.MyDubboServer"
   Dubbo triple pojo server started
   

10. 打开一个新的终端并启动客户端

    $ mvn org.codehaus.mojo:exec-maven-plugin:3.0.0:java -Dexec.mainClass="org.apache.dubbo.MyDubboClient"
    Received reply: message: "Hello, Demo!"
    

常见问题

1. 找不到 protobuf 类

由于 Triple 协议底层需要依赖 protobuf 协议进行传输，即使定义的服务接口没有使用 protobuf，也需要将 protobuf 依赖项引入环境。

         <dependency>
             <groupId>com.google.protobuf</groupId>
             <artifactId>protobuf-java</artifactId>
             <version>3.19.4</version>
         </dependency>