Java RPC简介

Java RPC

RPC，全称为Remote Procedure Call 即远程过程调用，它是一个计算机通信协议，它允许像调用本地服务一样调用远程服务。其核心思想就是：RPC能够让本地应用简单、高效地调用服务器中的过程（服务）。

要实现一个PRC框架，需要考虑一下几个问题：
（1）通信模型，在Java中一般基于BIO或NIO
（2）远程代理对象，对于Java而言，远程代理对象可以使用Java的动态对象实现，封装了调用远程方法调用
（3）序列化，将对象名称、方法名称、参数等对象信息进行网络传输需要转换成二进制传输

Java 实现RPC实例：

// Service 接口
public interface HelloService {
    String sayHi(String name);
}
// 实现类
public class HelloServiceImpl implements HelloService {
    public String sayHi(String name) {
        return "Hi, " + name;
    }
}
//Server接口
public interface Server {
    void stop();
    void start() throws IOException;
    void register(Class serviceInterface, Class impl);
    boolean isRunning();
    int getPort();
}
//Server具体类
public class ServiceCenter implements Server {
    private static ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
    private static final HashMap<String, Class> serviceRegistry = new HashMap<String, Class>();
    private static boolean isRunning = false;
    private static int port;
    public ServiceCenter(int port) {
        this.port = port;
    }
    public void stop() {
        isRunning = false;
        executor.shutdown();
    }
    public void start() throws IOException {
        ServerSocket server = new ServerSocket();
        server.bind(new InetSocketAddress(port));
        System.out.println("start server");
        try {
            while (true) {
                // 1.监听客户端的TCP连接，接到TCP连接后将其封装成task，由线程池执行
                executor.execute(new ServiceTask(server.accept()));
            }
        } finally {
            server.close();
        }
    }
    public void register(Class serviceInterface, Class impl) {
        serviceRegistry.put(serviceInterface.getName(), impl);
    }
    public boolean isRunning() {
        return isRunning;
    }
    public int getPort() {
        return port;
    }
    private static class ServiceTask implements Runnable {
        Socket clent = null;
        public ServiceTask(Socket client) {
            this.clent = client;
        }
        public void run() {
            ObjectInputStream input = null;
            ObjectOutputStream output = null;
            try {
                // 2.将客户端发送的码流反序列化成对象，反射调用服务实现者，获取执行结果
                input = new ObjectInputStream(clent.getInputStream());
                String serviceName = input.readUTF();
                String methodName = input.readUTF();
                Class<?>[] parameterTypes = (Class<?>[]) input.readObject();
                Object[] arguments = (Object[]) input.readObject();
                Class serviceClass = serviceRegistry.get(serviceName);
                if (serviceClass == null) {
                    throw new ClassNotFoundException(serviceName + " not found");
                }
                Method method = serviceClass.getMethod(methodName, parameterTypes);
                Object result = method.invoke(serviceClass.newInstance(), arguments);
                // 3.将执行结果反序列化，通过socket发送给客户端
                output = new ObjectOutputStream(clent.getOutputStream());
                output.writeObject(result);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (output != null) {
                    try {
                        output.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if (input != null) {
                    try {
                        input.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if (clent != null) {
                    try {
                        clent.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}
// 远程代理对象
public class RPCClient<T> {
    public static <T> T getRemoteProxyObj(final Class<?> serviceInterface, final InetSocketAddress addr) {
        // 1.将本地的接口调用转换成JDK的动态代理，在动态代理中实现接口的远程调用
        return (T) Proxy.newProxyInstance(serviceInterface.getClassLoader(), new Class<?>[]{serviceInterface},
                new InvocationHandler() {
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        Socket socket = null;
                        ObjectOutputStream output = null;
                        ObjectInputStream input = null;
                        try {
                            // 2.创建Socket客户端，根据指定地址连接远程服务提供者
                            socket = new Socket();
                            socket.connect(addr);
                            // 3.将远程服务调用所需的接口类、方法名、参数列表等编码后发送给服务提供者
                            output = new ObjectOutputStream(socket.getOutputStream());
                            output.writeUTF(serviceInterface.getName());
                            output.writeUTF(method.getName());
                            output.writeObject(method.getParameterTypes());
                            output.writeObject(args);
                            // 4.同步阻塞等待服务器返回应答，获取应答后返回
                            input = new ObjectInputStream(socket.getInputStream());
                            return input.readObject();
                        } finally {
                            if (socket != null) socket.close();
                            if (output != null) output.close();
                            if (input != null) input.close();
                        }
                    }
                });
    }
}
// 测试
public class RPCTest {
    public static void main(String[] args) throws IOException {
        new Thread(new Runnable() {
            public void run() {
                try {
                    Server serviceServer = new ServiceCenter(8088);
                    serviceServer.register(HelloService.class, HelloServiceImpl.class);
                    serviceServer.start();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
        HelloService service = RPCClient.getRemoteProxyObj(HelloService.class, new InetSocketAddress("localhost", 8088));
        System.out.println(service.sayHi("test"));
    }
}