介绍

传统 Echo 模型：

1. Java 客户端：键盘输入 -> 发送数据 -> Java 服务端
2. Java 服务端：接收数据 -> 处理数据 -> 发送数据 -> Java 客户端
3. Java 客户端：接收数据

样例代码

EchoServer

class HandlerThread implements Runnable {
    private Socket client;

    public HandlerThread(Socket client) {
        this.client = client;
    }

    @Override
    public void run() {
        try {
            PrintStream output = new PrintStream(client.getOutputStream());
            Scanner scanner = new Scanner(client.getInputStream());
            scanner.useDelimiter("\n");
            while (true) {
                if (scanner.hasNext()) {
                    // 注意不能漏掉 trim，因为最后还要一个换行符
                    String value = scanner.next().trim();
                    if ("bye".equalsIgnoreCase(value)) {
                        // 结束交互
                        output.println("[Echo] See you!");
                        break;
                    } else {
                        output.println("[Echo] " + value);
                    }
                }
            }
            client.close();
        } catch (Exception e) {}
    }
}


public class EchoServer {
    public static void main(String[] args) throws Exception{
        try (ServerSocket server = new ServerSocket(9090)) {
            while (true) {
                Socket client = server.accept();
                System.out.println("New connection established successfully!");
                new Thread(new HandlerThread(client)).start();
            }
        }
    }
}

EchoClient

public class EchoClient {
    static KeyboardInputReader keyboard = new KeyboardInputReader();

    public static void main(String[] args) throws Exception {
        try (Socket socket = new Socket(InetAddress.getLocalHost(), 9090)) {
            PrintStream output = new PrintStream(socket.getOutputStream());
            Scanner scanner = new Scanner(socket.getInputStream());
            scanner.useDelimiter("\n");
            while (true) {
                String value = 
                    keyboard.getStringNotNull("Please input data to be sent: ");
                output.println(value);
                if (scanner.hasNext()) {
                    System.err.println(scanner.next().trim());
                }
                if ("bye".equalsIgnoreCase(value)) {
                    break;
                }
            }
        }
    }
}