gRPC & High Performance APIs · 课时

简单的一元 gRPC 服务

使用生成的代码从头实现基础的“请求—响应”gRPC 服务和客户端

简单的一元 gRPC 服务 是 CoddyKit 上的免费 gRPC & High Performance APIs 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 gRPC & High Performance APIs 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 gRPC & High Performance APIs 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Unary RPC: Simple Interactions

In gRPC, a Unary RPC is the simplest communication pattern. It's like a traditional function call where a client sends a single request to the server, and the server responds with a single reply.

Think of it as a standard "request-response" model. The client waits for the server's response before proceeding.

Client sends one message.
Server sends one message back.
This is the most common RPC type.

Reviewing Our Protobuf

Before we dive into implementation, let's briefly recall our simple Protocol Buffer (Protobuf) definition. This schema defines the service and messages we'll use.

We'll implement the Greeter service with a SayHello method.

syntax = "proto3";

option java_multiple_files = true;
option java_package = "com.example.grpc.helloworld";
option java_outer_classname = "HelloWorldProto";

package helloworld;

service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

message HelloRequest {
  string name = 1;
}

message HelloReply {
  string message = 1;
}

(Remember, code generation was covered in a previous lesson.)

Server: Extending the Base

After generating code from our .proto file, gRPC creates an abstract base class for our server. For our Greeter service, it's GreeterGrpc.GreeterImplBase.

To implement our service, we create a new class that extends this base class and overrides the service method(s).

class GreeterImpl extends GreeterGrpc.GreeterImplBase {
    @Override
    public void sayHello(HelloRequest req,
                         StreamObserver<HelloReply> resObserver) {
        // ... implementation goes here ...
    }
}

The StreamObserver is how we send the response back.

Server Logic: Building Response

Inside the sayHello method, we receive the HelloRequest. We can then process it and build our HelloReply.

The StreamObserver.onNext() method sends the reply, and onCompleted() signals that the RPC is finished.

class GreeterImpl extends GreeterGrpc.GreeterImplBase {
    @Override
    public void sayHello(HelloRequest req,
                         StreamObserver<HelloReply> resObserver) {
        System.out.println("Received name: " + req.getName());
        HelloReply reply = HelloReply.newBuilder()
                                   .setMessage("Hello " + req.getName())
                                   .build();
        resObserver.onNext(reply);     // Send the response
        resObserver.onCompleted();  // Mark RPC as complete
    }
}

Full Server Implementation

Now, let's put it all together to create and start a gRPC server. This server will listen for incoming client requests on a specific port.

Try running this code and then proceed to the client implementation!

package com.example.grpc.helloworld;

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

import java.io.IOException;
import java.util.concurrent.TimeUnit;

public class HelloWorldServer {
    private Server server;

    private void start() throws IOException {
        int port = 50051;
        server = ServerBuilder.forPort(port)
                .addService(new GreeterImpl())
                .build()
                .start();
        System.out.println("Server started, listening on " + port);
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                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);
        }
    }

    private void blockUntilShutdown() throws InterruptedException {
        if (server != null) {
            server.awaitTermination();
        }
    }

    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) {
            System.out.println("Received: " + req.getName());
            HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName()).build();
            responseObserver.onNext(reply);
            responseObserver.onCompleted();
        }
    }
}

Client Stub: Connecting & Calling

On the client side, gRPC also generates "stubs." These stubs provide the methods to call the remote service, making it feel like a local method call.

For unary RPCs, we often use a blocking stub, which means the client waits for the server's response.

// Blocking stub for our Greeter service
GreeterGrpc.GreeterBlockingStub blockingStub;

The stub will handle all the underlying network communication details for you!

Client Channel: The Connection

Before using a stub, the client needs a channel. A channel represents a connection to a gRPC server at a specific host and port.

Channels are typically long-lived and can be reused for multiple RPC calls.

ManagedChannel channel = ManagedChannelBuilder.forAddress("localhost", 50051)
                                            .usePlaintext() // No TLS for simplicity
                                            .build();
blockingStub = GreeterGrpc.newBlockingStub(channel);

usePlaintext() is okay for local dev but avoid in production!

Full Client Implementation

With the channel and stub ready, we can now make our unary RPC call. We'll build a HelloRequest and send it via the stub.

Run the server from the previous step, then run this client to see it in action!

package com.example.grpc.helloworld;

import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;
import io.grpc.StatusRuntimeException;

import java.util.concurrent.TimeUnit;

public class HelloWorldClient {
    private final ManagedChannel channel;
    private final GreeterGrpc.GreeterBlockingStub blockingStub;

    public HelloWorldClient(String host, int port) {
        channel = ManagedChannelBuilder.forAddress(host, port)
                .usePlaintext() // For simplicity, no TLS
                .build();
        blockingStub = GreeterGrpc.newBlockingStub(channel);
    }

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

    public void greet(String name) {
        System.out.println("Will try to greet " + name + "...");
        HelloRequest request = HelloRequest.newBuilder().setName(name).build();
        HelloReply response;
        try {
            response = blockingStub.sayHello(request);
        } catch (StatusRuntimeException e) {
            System.err.println("RPC failed: " + e.getStatus());
            return;
        }
        System.out.println("Greeting: " + response.getMessage());
    }

    public static void main(String[] args) throws Exception {
        HelloWorldClient client = new HelloWorldClient("localhost", 50051);
        try {
            String user = "CoddyKit User";
            if (args.length > 0) {
                user = args[0];
            }
            client.greet(user);
        } finally {
            client.shutdown();
        }
    }
}

Unary Flow: Request & Reply

When you run the client, it sends the HelloRequest to the server. The server receives it, processes it using our GreeterImpl, and sends back a HelloReply.

Client: Creates channel, stub, builds HelloRequest.
Client: Calls blockingStub.sayHello(request).
Server: Receives HelloRequest in sayHello method.
Server: Processes, builds HelloReply, calls onNext() and onCompleted().
Client: Receives HelloReply, continues execution.

This completes one full unary RPC cycle!

Unary Service Check

Consider a gRPC unary service. Which component is responsible for receiving a request, processing it, and sending back a single response?

Recap: Simple Unary RPC

Great job! You've learned how to implement a basic unary gRPC service and client:

We reviewed the Protobuf schema for our service.
We implemented the server logic by extending the generated base class and handling requests.
We built a gRPC server instance and started it.
On the client side, we used a channel to connect and a blocking stub to make the RPC call.

Unary RPCs are fundamental to gRPC, providing a robust way for simple request-response communication. Next, we'll explore more advanced streaming patterns!

常见问题解答

「简单的一元 gRPC 服务」课时是免费的吗？

是的 — 「简单的一元 gRPC 服务」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 gRPC & High Performance APIs 课程的其余内容，请升级到 CoddyKit PRO。 gRPC & High Performance APIs 课程共包含 4 节课。

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