IDEA中基于web项目手写一个grpc

1、要定义protocol buffers，文件以.proto结尾，文件中定义message，message中定义成员变量（类型以及对应的序号），序号从1开始；定义服务（Service），服务中定义rpc的request和response。request和response分为流式和非流式，所以rpc可以分为四种类型。另外文件要指定编译的版本，编译后java类的包名，如果要用其他.proto文件中定义的消息，需要import进行导入。

proto语法：

syntax = "proto3";

option java_multiple_files = true;
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";
option objc_class_prefix = "HLW";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

　　

 

2、mvn编译可以让.proto文件生成对应的java类，这样就可以在java程序中使用。编译后，生成的java类在target文件夹下（IDEA开发工具，mvn进行依赖管理），proto文件每一个定义的Service，就会对应一个同名加上Grpc后缀的java类，那么问题转化为如何使用这样一个后缀为Grpc的类（客户端和服务端如何让编写）。

写客户端：

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grpc-java/examples/src/main/java/io/grpc/examples/helloworld/HelloWorldClient.java /
@ejona86
ejona86 examples: Allow passing target and simplify lifecycle
…
Latest commit 5b7f5b8 on 23 Jan
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 8 contributors
@ejona86@carl-mastrangelo@dapengzhang0@nmittler@steverao@zhangkun83@punkeel@jorgheymans
99 lines (90 sloc)  3.74 KB
  
/*
 * Copyright 2015 The gRPC Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.grpc.examples.helloworld;

import io.grpc.Channel;
import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.StatusRuntimeException;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * A simple client that requests a greeting from the {@link HelloWorldServer}.
 */
public class HelloWorldClient {
  private static final Logger logger = Logger.getLogger(HelloWorldClient.class.getName());

  private final GreeterGrpc.GreeterBlockingStub blockingStub;

  /** Construct client for accessing HelloWorld server using the existing channel. */
  public HelloWorldClient(Channel channel) {
    // 'channel' here is a Channel, not a ManagedChannel, so it is not this code's responsibility to
    // shut it down.

    // Passing Channels to code makes code easier to test and makes it easier to reuse Channels.
    blockingStub = GreeterGrpc.newBlockingStub(channel);
  }

  /** Say hello to server. */
  public void greet(String name) {
    logger.info("Will try to greet " + name + " ...");
    HelloRequest request = HelloRequest.newBuilder().setName(name).build();
    HelloReply response;
    try {
      response = blockingStub.sayHello(request);
    } catch (StatusRuntimeException e) {
      logger.log(Level.WARNING, "RPC failed: {0}", e.getStatus());
      return;
    }
    logger.info("Greeting: " + response.getMessage());
  }

  /**
   * Greet server. If provided, the first element of {@code args} is the name to use in the
   * greeting. The second argument is the target server.
   */
  public static void main(String[] args) throws Exception {
    String user = "world";
    // Access a service running on the local machine on port 50051
    String target = "localhost:50051";
    // Allow passing in the user and target strings as command line arguments
    if (args.length > 0) {
      if ("--help".equals(args[0])) {
        System.err.println("Usage: [name [target]]");
        System.err.println("");
        System.err.println("  name    The name you wish to be greeted by. Defaults to " + user);
        System.err.println("  target  The server to connect to. Defaults to " + target);
        System.exit(1);
      }
      user = args[0];
    }
    if (args.length > 1) {
      target = args[1];
    }

    // Create a communication channel to the server, known as a Channel. Channels are thread-safe
    // and reusable. It is common to create channels at the beginning of your application and reuse
    // them until the application shuts down.
    ManagedChannel channel = ManagedChannelBuilder.forTarget(target)
        // Channels are secure by default (via SSL/TLS). For the example we disable TLS to avoid
        // needing certificates.
        .usePlaintext()
        .build();
    try {
      HelloWorldClient client = new HelloWorldClient(channel);
      client.greet(user);
    } finally {
      // ManagedChannels use resources like threads and TCP connections. To prevent leaking these
      // resources the channel should be shut down when it will no longer be used. If it may be used
      // again leave it running.
      channel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
    }
  }
}

　　

 

可以看到：（1）编写client的时候，定义了一个： private final GreeterGrpc.GreeterBlockingStub blockingStub;

这个变量是一个存根，用于本地调用，并且还是一个Blocking（阻塞的）的存根，或者说是同步调用的存根，要等待服务端返回结果，才会接着执行下面的逻辑。

（2）blockingStub = GreeterGrpc.newBlockingStub(channel)，构造方法传入的是Channel，通道，提供ip和端口号进行rpc通信。

（3）利用stub来调用rpc方法，返回值是定义的response类。像上面的sayHello方法

编写服务端：

package io.grpc.examples.helloworld;

import io.grpc.Server;
import io.grpc.ServerBuilder;
import io.grpc.stub.StreamObserver;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

/**
 * Server that manages startup/shutdown of a {@code Greeter} server.
 */
public class HelloWorldServer {
  private static final Logger logger = Logger.getLogger(HelloWorldServer.class.getName());

  private Server server;

  private void start() throws IOException {
    /* The port on which the server should run */
    int port = 50051;
    server = ServerBuilder.forPort(port)
        .addService(new GreeterImpl())
        .build()
        .start();
    logger.info("Server started, listening on " + port);
    Runtime.getRuntime().addShutdownHook(new Thread() {
      @Override
      public void run() {
        // Use stderr here since the logger may have been reset by its JVM shutdown hook.
        System.err.println("*** shutting down gRPC server since JVM is shutting down");
        try {
          HelloWorldServer.this.stop();
        } catch (InterruptedException e) {
          e.printStackTrace(System.err);
        }
        System.err.println("*** server shut down");
      }
    });
  }

  private void stop() throws InterruptedException {
    if (server != null) {
      server.shutdown().awaitTermination(30, TimeUnit.SECONDS);
    }
  }

  /**
   * Await termination on the main thread since the grpc library uses daemon threads.
   */
  private void blockUntilShutdown() throws InterruptedException {
    if (server != null) {
      server.awaitTermination();
    }
  }

  /**
   * Main launches the server from the command line.
   */
  public static void main(String[] args) throws IOException, InterruptedException {
    final HelloWorldServer server = new HelloWorldServer();
    server.start();
    server.blockUntilShutdown();
  }

  static class GreeterImpl extends GreeterGrpc.GreeterImplBase {

    @Override
    public void sayHello(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
      HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName()).build();
      responseObserver.onNext(reply);
      responseObserver.onCompleted();
    }
  }
}

　　

可以看到如何编写服务端:(1)定义一个类，实现GreeterGrpc.GreeterImplBase，重写方法sayHello，返回自定义的返回值。

 

另外如果只是想在rpc是无参数的，可以通过先

import "google/protobuf/empty.proto";（不是特别确定在这个proto文件中）
再使用

google.protobuf.Empty类型，也可以使用proto的boolean类型，google.protobuf.BoolValue

比如：

rpc deleteAgent (google.protobuf.Empty) returns (google.protobuf.BoolValue);

另外关于服务端中的StreamObserver，参考：https://blog.csdn.net/u010900754/article/details/106203724。
关于简单的grpc例子，参考：http://doc.oschina.net/grpc?t=60134#client