Pojo 序列化兼容模式

Pojo 序列化兼容模式

这篇教程会通过从零构建一个简单的工程来演示如何基于 POJO 方式使用 Dubbo Triple, 在应用不改变已有接口定义的同时升级到 Triple 协议。此模式下 Triple 使用方式与 Dubbo 协议一样。

前置条件

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

创建工程

首先创建一个空的 maven 工程

$ 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

切换到工程目录
```
$ cd tri-pojo-demo
```

在 pom.xml 中设置 JDK 版本，添加 Dubbo 依赖和插件

<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>

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);
}

添加服务端接口实现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 + "!";
   }
}

添加服务端启动类 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();
   }
}

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);
    }
}

编译代码
```
$ mvn clean install
```

启动服务端

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

打开新的终端，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

protobuf 类找不到

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不使用 protobuf 也需要在环境中引入 protobuf 的依赖。

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

最后修改 December 16, 2022: Fix check (#1736) (97972c1)