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有两个程序：客户端（Client）、服务端（Server）

客户端：

import java.io.*;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;

public class Client {
    Socket socket;

    public static void main(String[] args) throws IOException {
        Client client = new Client(InetAddress.getLocalHost(), Server.port);
        client.sendMes();
    }

    public Client(String ip, int port) throws IOException {
        this.socket = new Socket(ip, port);
    }

    public Client(InetAddress ip, int port) throws IOException {
        this.socket = new Socket(ip, port);
    }

    public void sendMes() throws IOException {
        OutputStream os = socket.getOutputStream();
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os));
        bw.write("hello");
        bw.newLine();
        bw.write("123");
        bw.newLine();
        bw.flush();
        bw.close();
        System.out.println("发送成功！");

    }

    /**
     * 接受服务端返回的消息
     * @throws IOException
     */
    public void receiveMes() throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        System.out.println(br.readLine());
    }

}

服务端：

import java.io.*;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {
    ServerSocket serverSocket;
    Socket socket;

    static int port = 9999;


    public static void main(String[] args) throws IOException {
        Server server = new Server(port);
        server.start1();
        server.respond();
    }

    public Server(int port) throws IOException {
        serverSocket = new ServerSocket(port);
        socket = serverSocket.accept();
    }

    /**
     * 服务端接受数据
     * 步骤：
     *      1. 创建 socket，用于接收数据
     *      2. 用 socket.getInputStream() 接受通道里的数据
     *      3. 用 BufferRead 读取，并显示
     *
     * @throws IOException
     */
    public void start1() throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String line;
        while ( !((line = br.readLine()).equals("\n")) ) {
            System.out.println(line);
        }
//        System.out.println(br.readLine());
        socket.shutdownInput();
        System.out.println("服务端接收成功");

    }

    /**
     * 服务端回应客户端
     * @throws IOException
     */
    public void respond() throws IOException {
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
        bw.write("nihao");
        bw.newLine();
        bw.flush();
        bw.close();
    }

    public void close() throws IOException {
        socket.close();
        serverSocket.close();
    }

}

Client里面的newLine()并不是表示流的结束，因此当没有close()时，在Server里 循环readLine()是不能结束循环的，一直在等待Client的继续传输，程序一直卡住。

而当加入close()时，Server可以顺利读取Client传输的数据，但是此时，Client的socket也随着流的关闭而关闭了，导致Server响应Client的数据就无法传输给Client。

PS：所有的读取，只要流没结束  就不会停下来。如果没有了 ，那就会等待，如果有，那就直接读。