gRPC java 如何使用 grpc gateway java

本文使用gRPC框架Java语言版本构建一个helloworld项目。涉及到的内容有：
① 通过.proto文件生成Java代码的方法。
② 以及服务端和客户端代码使用示例。
本文先不讲解代码细节，只用来帮助自己构造一个Java版本的gRPC项目。后续系列文章再说，最后把代码放到github上。

一、环境准备

1.1 安装protocbuf

首先需要安装protocbuf 3.x版本。本文中，我以3.17.2版本为例。
把下面代码复制到一个shell脚本中，然后执行，就可以安装protocbuf-3.17.2。

#!/bin/bash
export CXXFLAGS="-I/usr/local/include" LDFLAGS="-L/usr/local/lib"
PROTOBUF_VERSION=3.17.2
curl -LO https://github.com/protocolbuffers/protobuf/releases/download/v$PROTOBUF_VERSION/protobuf-all-$PROTOBUF_VERSION.tar.gz
tar xzf protobuf-all-$PROTOBUF_VERSION.tar.gz
cd protobuf-$PROTOBUF_VERSION
./configure --disable-shared
make   # You may want to pass -j to make this run faster; see make --help
sudo make install

最后执行protoc --version来验证是否安装成功

1.2 安装Maven

使用IDEA内置的maven即可。如果不想用IDEA自带的maven，可以随便到网上找个教程。（最好找版本比较新的，我用的是3.5.2版本，大家可以安装比这个更新的版本）

二、gRPC项目构建

2.1 新建maven项目并修改pom.xml

首先用IDEA新建一个maven项目。

接着在pom.xml中添加如下代码，注意这个build标签和properties标签都是project标签的直接子标签。

<properties>
        <protobuf.version>3.17.2</protobuf.version>
        <protoc.version>3.17.2</protoc.version>
        <grpc.version>1.41.0</grpc.version>
    </properties>

    <build>
        <extensions>
            <extension>
                <groupId>kr.motd.maven</groupId>
                <artifactId>os-maven-plugin</artifactId>
                <version>1.6.2</version>
            </extension>
        </extensions>
        <plugins>
            <plugin>
                <groupId>org.xolstice.maven.plugins</groupId>
                <artifactId>protobuf-maven-plugin</artifactId>
                <version>0.6.1</version>
                <configuration>
                    <protocArtifact>com.google.protobuf:protoc:${protoc.version}:exe:${os.detected.classifier}</protocArtifact>
                    <pluginId>grpc-java</pluginId>
                    <pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc.version}:exe:${os.detected.classifier}</pluginArtifact>
                    <protoSourceRoot>src/main/proto</protoSourceRoot>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>compile-custom</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

再接着我们继续在pom.xml中添加一些，这些依赖是构造gRPC-java项目必须用到的（来自官方文档）。

<dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-netty-shaded</artifactId>
            <version>1.41.0</version>
        </dependency>
        <dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-protobuf</artifactId>
            <version>1.41.0</version>
        </dependency>
        <dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-stub</artifactId>
            <version>1.41.0</version>
        </dependency>
        <dependency>
            <groupId>com.google.protobuf</groupId>
            <artifactId>protobuf-java-util</artifactId>
            <version>${protobuf.version}</version>
        </dependency>
        <dependency> <!-- necessary for Java 9+ -->
            <groupId>org.apache.tomcat</groupId>
            <artifactId>annotations-api</artifactId>
            <version>6.0.53</version>
            <scope>provided</scope>
        </dependency>

2.2 添加.proto文件

proto文件用来描述rpc请求体、响应体、以及rpc提供的服务。通过插件可以根据.proto文件生成Java类。

这里面有个非常重要的点要注意，就是proto文件存放的位置。一定要在和src/main/java源文件目录同级的proto源文件目录才可以。如下图所示：

我们添加一个proto文件：helloworld.proto

// 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.
syntax = "proto3";

option java_multiple_files = true;
option java_package = "com.zhb.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;
}

这里面还有一个小细节，就是proto文件中有一行代码是：
option java_package = "com.zhb.grpc.examples.helloworld"; 这个代表生成的代码属于哪个package。

2.3 根据.proto文件生成消息体类文件和XXXGrpc类文件

在第一步修改的pom.xml的路径下，首先执行：

mvn protobuf:compile 生成消息体类文件:

接着执行：

mvn protobuf:compile-custom 生成XXXGrpc类文件：

2.4 编写业务代码

经过2.1–2.3的步骤之后，我们的准备工作都做完了。该生成的代码也都生成了，接下来就是编写业务代码了。

ps：注意下Java类所属的package

服务端代码：

/*
 * 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 com.zhb.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();
    }
  }
}

客户端代码：

/*
 * 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 com.zhb.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);
    }
  }
}

然后先启动Server：

再启动Client：

可以看到执行成功。一个简单的gRPC helloworld工程就搭建好了。