2018/06/09 Getting Started with gRPC

grpc 是 google 开发的一个支持多种语言的远程调用类库。使用 grpc ，客户端程序可以像调用本地方法一样直接调用不同机器上的服务方法。
https://grpc.io/img/landing-2.svg
使用 grpc 能够使用不同语言来编写服务端和客户端，并可以很容易进行集成。
grpc 是一个高效的 rpc 库，默认使用 protocol buffers 。通过 protocol buffers 的定义语言可以定义服务的参数及返回值，然后通过 protoc 编译器生成服务器端和客户端代码。

java-grpc

以 java 语言为例，首先定义 proto 。

syntax = "proto3";

option java_multiple_files = true;
option java_package = "com.rolex.grpc.helloworld"; // 生成 java 代码的包名
option java_outer_classname = "HelloWorldProto"; // 生成 java 代码的类名
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;
}

proto 定义好以后，就可以生成代码了。 生成 Java 版的代码有两种方式，一是安装 protoc 编译器，进行编译；二是使用插件，这种方法比较简单，方便开发。以 maven 插件为例，pom.xml 文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.rolex</groupId>
    <artifactId>grgc-samples</artifactId>
    <version>1.0-SNAPSHOT</version>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <grpc.version>1.12.0</grpc.version>
        <junit.version>4.12</junit.version>
        <os-maven-plugin.version>1.5.0.Final</os-maven-plugin.version>
        <protobuf-maven-plugin.version>0.5.0</protobuf-maven-plugin.version>
        <netty.tcnative.version>2.0.7.Final</netty.tcnative.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-netty</artifactId>
            <version>${grpc.version}</version>
        </dependency>
        <dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-protobuf</artifactId>
            <version>${grpc.version}</version>
        </dependency>
        <dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-stub</artifactId>
            <version>${grpc.version}</version>
        </dependency>
        <dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-alts</artifactId>
            <version>${grpc.version}</version>
        </dependency>
        <dependency>
            <groupId>io.grpc</groupId>
            <artifactId>grpc-testing</artifactId>
            <version>${grpc.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-tcnative-boringssl-static</artifactId>
            <version>${netty.tcnative.version}</version>
        </dependency>
        <dependency>
            <groupId>com.google.api.grpc</groupId>
            <artifactId>proto-google-common-protos</artifactId>
            <version>1.0.0</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>2.18.3</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <extensions>
            <extension>
                <groupId>kr.motd.maven</groupId>
                <artifactId>os-maven-plugin</artifactId>
                <version>1.5.0.Final</version>
            </extension>
        </extensions>
        <plugins>
            <plugin>
                <groupId>org.xolstice.maven.plugins</groupId>
                <artifactId>protobuf-maven-plugin</artifactId>
                <version>0.5.1</version>
                <configuration>
                    <protocArtifact>com.google.protobuf:protoc:3.5.1-1:exe:${os.detected.classifier}</protocArtifact>
                    <pluginId>grpc-java</pluginId>
                    <pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc.version}:exe:${os.detected.classifier}</pluginArtifact>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>compile-custom</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

使用 os-maven-plugin 插件，不用关心系统要使用的编译器版本和路径。

写好 pom 后使用命令 mvn clean compile 即可生成相关代码。

编写测试程序，服务端代码：

import io.grpc.Server;
import io.grpc.ServerBuilder;
import io.grpc.stub.StreamObserver;
import java.io.IOException;
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");
        HelloWorldServer.this.stop();
        System.err.println("*** server shut down");
      }
    });
  }

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

  /**
   * 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();
  }

  public 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：

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 ManagedChannel channel;
  private final GreeterGrpc.GreeterBlockingStub blockingStub;

  /** Construct client connecting to HelloWorld server at {@code host:port}. */
  public HelloWorldClient(String host, int port) {
    this(ManagedChannelBuilder.forAddress(host, port)
        // Channels are secure by default (via SSL/TLS). For the example we disable TLS to avoid
        // needing certificates.
        .usePlaintext(true)
        .build());
  }

  /** Construct client for accessing RouteGuide server using the existing channel. */
  public HelloWorldClient(ManagedChannel channel) {
    this.channel = channel;
    blockingStub = GreeterGrpc.newBlockingStub(channel);
  }

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

  /** 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.
   */
  public static void main(String[] args) throws Exception {
    HelloWorldClient client = new HelloWorldClient("localhost", 50051);
    try {
      /* Access a service running on the local machine on port 50051 */
      String user = "world";
      if (args.length > 0) {
        user = args[0]; /* Use the arg as the name to greet if provided */
      }
      client.greet(user);
    } finally {
      client.shutdown();
    }
  }
}

先启动服务端程序，再执行客户端代码可看到结果。
以上是一个简单 rpc 的例子，即客户端向服务端发送一个请求，然后服务端返回一个响应。除此之外，还可以创建服务器端或客户端的 streaming RPC 进行交互，可参考 https://github.com/grpc/grpc-java/tree/master/examples 。



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