https://zhuanlan.zhihu.com/p/24911086 demo ServerSocket

Server.java

package net;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.*;

public class Server {
    public static void main(String[] args) throws IOException {
    	ServerSocket ss = new ServerSocket(8080);
    	Socket conn = ss.accept();
    	BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    	BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(conn.getOutputStream()));
    	String s = br.readLine();
    	
    	while(s != null ) {
    		System.out.println(s);
    		bw.write(s.toUpperCase() + '\n');
    		bw.flush();
    		s = br.readLine();
    	}
    	
    	br.close();
    	bw.close();
    	conn.close();
    }
}