Data transmission under the same LAN based on tcp/ip

1.TCP/IP Network programming

    When developing web applications , Will meet Socket The concept . An application passes through a Socket To establish a remote connection , and Socket Through internal TCP/IP The protocol transmits data to the network .

    TCP/IP It is the abbreviation of transmission control protocol and network protocol , It defines how devices connect to the Internet , And how data is transferred between them .TCP/IP It's not an agreement , It's an umbrella term for a family of agreements , It includes IP agreement 、ICMP agreement 、TCP agreement 、 as well as http、ftp、pop3 Agreements, etc , Network computers are interconnected by this protocol family .

2. The data transfer

  Use Socket When programming the network , In essence, it is the network communication between two processes . One of the processes must act as the server side , It will actively listen to the port at a specified location , A column must act as a client , It must actively connect with the server IP Address and specified port , If the connection is successful , The server and client have successfully established a TCP agreement , Both parties can send and receive data at any time .

  For the server side , its Socket Is specified IP Address and specified port number .

  For clients , its Socket It's on the computer IP Address and a random port number assigned by the operating system .

3. Server side

Java The standard library provides ServerSocket To implement the specified IP Listening on the specified port of . The implementation procedure is as follows ：

public class Server {
    public static void main(String[] args) throws IOException {

        ServerSocket ss = new ServerSocket(6666); //  Listen on the specified port 
        System.out.println("server is running...");
        // Use while Loop to keep the server in the receiving state 
        while (true) {
            Socket sock = ss.accept();
            
            //  Use Socket Stream for network communication 
            // ...
            
            System.out.println("connected from " + sock.getRemoteSocketAddress());
        }
    }
}

  It should be noted that ：

（1） Use try-catch Block to throw an exception

（2） Use while Loop to keep the server in the receiving state .

（3） Be sure to specify the listening port on the server .

4. client

      The client connects to the server through the following code , And be sure to specify the port of the server , Otherwise, data transmission will not be carried out correctly .

public class Client {
    public static void main(String[] args) throws IOException {
        //  Connect to the specified server and port 
        Socket sock = new Socket("localhost", 6666); 
        
       //  Use Socket Stream for network communication 
       // ...
        
        //  close 
        sock.close();
        System.out.println("disconnected.");
    }
}

5. The reference sample ：（ The server · Chat with clients on the same LAN ）

Server side ：

public static void main(String[] args) {

		Scanner input = new Scanner(System.in);
		try (DatagramSocket socket = new DatagramSocket(8888)) {
			DatagramPacket sendPacket = new DatagramPacket(new byte[1024], 1024,
					new InetSocketAddress("192.168.254.177", 9999));
			DatagramPacket receivePacket = new DatagramPacket(new byte[1024], 1024);

			while (true) {

				socket.receive(receivePacket);
				String receiveContent = new String(receivePacket.getData(), receivePacket.getOffset(),
						receivePacket.getLength());
				if (receiveContent.equals("over")) {
					System.out.println(" The other party quit chatting ......");
					break;
				}
				System.out.println(" It said " + receiveContent);

				System.out.print(" You say? ：");
				String sendContent = input.nextLine();
				sendPacket.setData(sendContent.getBytes());
				socket.send(sendPacket);
				if (sendContent.equals("over")) {
					System.out.println(" You quit chatting ...");
					return;
				}

			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

client ：

public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		
		while(true) {
			
			
			try (Socket cilent = new Socket("192.168.254.159", 8888);
                
				 BufferedWriter writer = new BufferedWriter(new 
                     OutputStreamWriter(cilent.getOutputStream()));
				 BufferedReader reader = new BufferedReader(new 
                     InputStreamReader(cilent.getInputStream()))
				) {
				// Get console input 
				String question = input.nextLine();
				if(question.equals("over")) {
					break;
				}

				//  Send a message to the server 
				writer.write(question);
				writer.flush();
				
				// Temporarily end this output 
				cilent.shutdownOutput();
				
				// Get the answer from the server 
				String answer = reader.readLine();
				System.out.println("【 client 】 Answer from the server " + answer);
				

			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
		System.out.println(" This chat is over ！!");
	}