Pojo Serialization Compatibility Mode

This tutorial will build a simple project from scratch to demonstrate how to use Dubbo Triple based on POJO, and upgrade to the Triple protocol while the application does not change the existing interface definition. **In this mode, Triple is used in the same way as Dubbo protocol. **

For specific use cases, please refer to: [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);

precondition

• JDK version >= 8
• Installed Maven
• Installed and started Zookeeper

Create project

1. First create an empty maven project

   $ 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. Switch to the project directory

   $ cd tri-pojo-demo
   

3. Set JDK version in pom.xml, add Dubbo dependencies and plugins

   <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. Add interface definition src/main/java/org/apache/dubbo/Greeter.java

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

5. Add server-side interface implementation 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. Add server startup class 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. Add the client startup class 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. Compile the code

   $ mvn clean install
   

9. Start the server

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

10. Open a new terminal and start the client

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

common problem

1. protobuf class not found

Since the bottom layer of the Triple protocol needs to rely on the protobuf protocol for transmission, even if the defined service interface does not use protobuf, it is necessary to introduce protobuf dependencies into the environment.

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