Advanced API (batch image Download & socket dialog)

File character stream ：
         *         FileReader
         *         FileWriter

Read ：
         *                  One character array can be read at a time read(buf)
write in ：
         *                 write(char)
         *                 write(char[] chs)
         *                 write(String str)

    Buffer flow
         *         BufferedReader
         *         BufferedWriter
         * 
         *         readLine();// Read a line
         *         newLine();// enjambment
         *         flush();// Refresh buffer

Converted flow
         *         InputStreamReader
         *         OutputStreamWriter

    System.out.println("--------------- The server ----------------");
        //1. Create server side   adopt ServerSocket
        ServerSocket ss = new ServerSocket(8989);
        System.out.println("QQ Server turned on .... Wait for the client to connect !!!");
        //2. Wait for a client to connect to the server
        // adopt ss Object to call the method of the receiving client
        Socket sk = ss.accept();// The way of blocking
        System.out.println(" A client is online ......");
        
        // Receive messages from clients
        InputStream is = sk.getInputStream();
        InputStreamReader isr = new InputStreamReader(is);
        BufferedReader br = new BufferedReader(isr);
        
        // Read a line
        String readLine = br.readLine();
        System.out.println(" client sb say : "+readLine);
        
        // reply
        OutputStream os = sk.getOutputStream();
        OutputStreamWriter osw = new OutputStreamWriter(os);
        BufferedWriter bw = new BufferedWriter(osw);
        // Send a message
        Scanner sc = new Scanner(System.in);
        System.out.println(" Please enter the content to send : ");
        String content = sc.next();
        bw.write(content);
        bw.newLine();
        bw.flush();

System.out.println("------------------------ client --------------------");
        // 1. Use Socket Create client
        Socket sk = new Socket(InetAddress.getByName("127.0.0.1"), 8989);
        System.out.println(" Client on , Successfully connected to the server ");

        // a key : When the client connects to the server Send a message Flow through the network
        OutputStream os = sk.getOutputStream();
        OutputStreamWriter osw = new OutputStreamWriter(os);
        BufferedWriter bw = new BufferedWriter(osw);
        // Send a message
        // String content = " Hello , The server ; I'm the client , I like drinking .";
        Scanner sc = new Scanner(System.in);
        System.out.println(" Please enter the content to send : ");
        String content = sc.next();
        bw.write(content);
        bw.newLine();
        bw.flush();

        // Receive messages from clients
        InputStream is = sk.getInputStream();
        InputStreamReader isr = new InputStreamReader(is);
        BufferedReader br = new BufferedReader(isr);

        // Read a line
        String readLine = br.readLine();
        System.out.println(" The server sb say : " + readLine);