grpc-java入门实例
本文主要介绍如何在Intellij IDEA环境下，快速搭建出grpc-java的入门实例。这个入门实例是一个HelloWorld程序，客户端发送world到服务端，服务端接收到请求后，拼装成 Hello,world返回。
环境配置
JDK1.8
Maven 3.6
Intellij IDEA
创建一个Project
使用Maven自带的maven-archetype-webapp原型创建一个webapp项目，在src/main下新建对应的java和proto文件夹，并将java文件夹转换为 Source Root，项目结构如下图所示：
pom文件中引入相关依赖和插件
io.grpc
grpc-netty-shaded
1.27.2
io.grpc
grpc-protobuf
1.27.2
io.grpc
grpc-stub
1.27.2
grpc-java
kr.motd.maven
os-maven-plugin
1.6.2
org.xolstice.maven.plugins
protobuf-maven-plugin
0.6.1
com.google.protobuf:protoc:3.11.0:exe:${os.detected.classifier}
grpc-java
io.grpc:protoc-gen-grpc-java:1.27.2:exe:${os.detected.classifier}
compile
compile-custom
编写.proto文件，定义服务接口
在proto文件夹下编写一个helloworld.proto文件，内容如下：
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;
}
通过protocol buffer编译器生成服务端和客户端代码
选中Project，执行Maven Compile操作，会在target/generate-sources下生成对应的代码。
使用Java gRPC API为上面定义的服务接口编写客户端和服务端
在src/main/java文件夹下新建，io.grpc.examples.helloworldPackage，并将代码放在此文件夹下，与helloworld.proto文件中指定的java_package参数对应。（如果放在其它文件夹下，代码要做适当调整，因为代码的引用位置变了）。
客户端代码
HelloWorldClient.java
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()
.build());
}
/** Construct client for accessing HelloWorld server using the existing channel. */
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 {
// Access a service running on the local machine on port 50051
HelloWorldClient client = new HelloWorldClient("localhost", 50051);
try {
String user = "world";
// Use the arg as the name to greet if provided
if (args.length > 0) {
user = args[0];
}
client.greet(user);
} finally {
client.shutdown();
}
}
}
服务端代码
HelloWorldServer.java
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 responseObserver) {
HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName()).build();
responseObserver.onNext(reply);
responseObserver.onCompleted();
}
}
}
执行代码
先运行HelloWorldServer，再运行HelloWorldClient，结果如下：
有兴趣的话可以改改这个示例，然后看看运行效果。
注意：
如果想在Eclipse环境运行该实例，需要注意以下几个不同点：
- pom文件中插件引用
Intellij中：
kr.motd.maven
os-maven-plugin
1.6.2
eclipse中：
kr.motd.maven
os-maven-plugin
1.6.1
initialize
detect
- .proto文件经过IDE编译后生成的代码引用问题
Intellij中可以直接引用target目录下生成的protobuf代码，eclipse下不行，需要将生成的文件copy到src/main/java对应的文件夹下（和.proto中配置的java_package参数一致）。另外，因为jdk编译版本的问题，文件copy过后，需要去掉一些@java.lang.Override，否则代码报错（网上查阅资料，jdk高与1.6版本后就会有这个问题，具体没有测试过）。
参考资料
gRPC Quick Start
grpc-java源码地址