protoBuf 实现客户端与服务端

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1.定义消息格式

　　在 src/main/proto 目录下创建 person.proto 文件，并定义消息格式，例如：

syntax = "proto3";
package example;

message Person {
  string name = 1;
  int32 age = 2;
  repeated string interests = 3;
}

　　这个文件定义了一个名为 Person 的消息类型，包括三个字段：name、age 和 interests

2.生成代码

　　使用 protoc 工具来生成 Java 代码，需要安装相应的插件和工具，可以通过 Maven 或 Gradle 等构建工具自动下载和配置。这里演示手动下载和安装的方式。

　　首先下载 protoc 工具及其插件，例如从官方网站下载对应版本的 protoc-3.x.x-linux-x86_64.zip，以及 protoc-gen-grpc-java 插件，例如从 Maven 中央仓库下载最新版的 protoc-gen-grpc-java-1.42.0-linux-x86_64.exe。

　　然后解压 protoc 工具，将 protoc 命令所在的路径添加到环境变量 PATH 中，例如：

export PATH="/path/to/protoc/bin:$PATH"

　　接下来安装 protobuf-java 和 grpc-java 两个依赖，例如通过 Maven 引入以下依赖：

<dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java</artifactId>
  <version>3.17.3</version>
</dependency>

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-netty-shaded</artifactId>
  <version>1.42.0</version>
</dependency>

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-protobuf</artifactId>
  <version>1.42.0</version>
</dependency>

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-stub</artifactId>
  <version>1.42.0</version>
</dependency>

<dependency>
  <groupId>io.grpc</groupId>
  <artifactId>grpc-testing</artifactId>
  <version>1.42.0</version>
  <scope>test</scope>
</dependency>

　　接着使用 protoc 生成 Java 代码，例如：

protoc --java_out=src/main/java --grpc-java_out=src/main/java src/main/proto/person.proto

　　这个命令会在 src/main/java/example 目录下生成 Person.java、PersonGrpc.java 和 PersonGrpc$PersonStub.java 等文件。

3.实现服务端

package example;

import io.grpc.Server;
import io.grpc.ServerBuilder;
import io.grpc.stub.StreamObserver;

import java.io.IOException;

public class PersonServer {
    private final int port;
    private final Server server;

    public PersonServer(int port) throws IOException {
        this.port = port;
        this.server = ServerBuilder.forPort(port)
                .addService(new PersonServiceImpl())
                .build();
    }

    public void start() throws IOException {
        server.start();
        System.out.println("Server started, listening on " + port);
        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            System.err.println("*** shutting down gRPC server since JVM is shutting down");
            PersonServer.this.stop();
            System.err.println("*** server shut down");
        }));
    }

    public void stop() {
        if (server != null) {
            server.shutdown();
        }
    }

    private static class PersonServiceImpl extends PersonGrpc.PersonImplBase {
        @Override
        public void getMessage(PersonRequest request, StreamObserver<PersonResponse> responseObserver) {
            String name = request.getName();
            int age = request.getAge();
            String interests = String.join(", ", request.getInterestsList());
            
            // 将请求的内容响应回去
            PersonResponse response = PersonResponse.newBuilder()
                    .setMessage("Received person info: name=" + name + ", age=" + age + ", interests=[" + interests + "]")
                    .build();
            responseObserver.onNext(response);
            responseObserver.onCompleted();
        }
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        PersonServer server = new PersonServer(8989);
        server.start();
        server.blockUntilShutdown();
    }
}

4.实现客户端

package example;

import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.stub.StreamObserver;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class PersonClient {
    private final ManagedChannel channel;
    private final PersonGrpc.PersonStub stub;

    public PersonClient(String host, int port) {
        this.channel = ManagedChannelBuilder.forAddress(host, port)
                .usePlaintext()
                .build();
        this.stub = PersonGrpc.newStub(channel);
    }

    public void shutdown() throws InterruptedException {
        channel.shutdown().awaitTermination(5, TimeUnit.SECONDS);
    }

    public void sendMessage(String name, int age, String... interests) throws InterruptedException {
        final CountDownLatch latch = new CountDownLatch(1);

        StreamObserver<PersonResponse> responseObserver = new StreamObserver<PersonResponse>() {
            @Override
            public void onNext(PersonResponse response) {
                System.out.println("Received response: " + response.getMessage());
            }

            @Override
            public void onError(Throwable t) {
                System.err.println("Received error: " + t.getMessage());
                latch.countDown();
            }

            @Override
            public void onCompleted() {
                System.out.println("Request completed");
                latch.countDown();
            }
        };

        List<String> interestList = Arrays.asList(interests);
        PersonRequest request = PersonRequest.newBuilder()
                .setName(name)
                .setAge(age)
                .addAllInterests(interestList)
                .build();

        stub.getMessage(request, responseObserver);

        latch.await();
    }

    public static void main(String[] args) throws InterruptedException {
        PersonClient client = new PersonClient("localhost", 8989);

        // 向服务器发送请求
        client.sendMessage("Alice", 20, "reading", "swimming");

        // 关闭连接
        client.shutdown();
    }
}

　　这个客户端会向服务器发送一个包含 name、age 和 interests 字段的 PersonRequest 消息，并等待接收服务器的响应信息。

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