I. Socket sockets

• Two programs on the network communicate through a two-way connection to realize data exchange. One end of the connection is called a socket.
• Using socket to develop TCP program in java, this method can easily establish reliable, bidirectional, persistent, point-to-point communication connection.
• In the development of socket program, the server side uses ServerSocket to wait for the connection of the client. For the java network program, each client is represented by a socket object.

Code examples

2.1 Complete a communication between server and client

• Communicate with the client as a server.
• The server waits for the connection of the client and sends the data to the client after the connection.

Server

package com.rrs.socketserver;

import java.io.IOException;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

import org.junit.Test;

/**
 * @author lzx
 * on 2019/9/25.
 */
public class SocketServer {

	@Test
	public void test01() throws IOException {

		System.out.println("socket server start...");
		ServerSocket serverSocket = new ServerSocket(8888);

		Socket socket = serverSocket.accept();
		System.out.println("Client detected socket: " + socket);

		OutputStream out = socket.getOutputStream();

		String mString = "Hello Client";
		byte[] bytes = mString.getBytes();

		out.write(bytes);

		socket.shutdownOutput();
		out.close();

	}

}

Client

package com.rrs.sockerclient;

import java.io.IOException;
import java.io.InputStream;
import java.net.Socket;
import java.net.SocketAddress;

/**
 * Created by lzx on 2019/9/25.
 */
public class SocketClient {


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

        System.out.println("socket client start...");
        Socket socketClient = null;


        socketClient = new Socket("127.0.0.1", 8888);
        InputStream in = socketClient.getInputStream();
        byte[] bytes = new byte[1024];

        int len = in.read(bytes);

        String msg = new String(bytes, 0, len);

        System.out.println(msg);
    }

}

2.2 Complete picture transmission from client to server

Server server waits for client to send pictures

package com.rrs.socketserver.server;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;

import org.junit.Test;

/**
 * @author lzx
 *
 */
public class ServerPic {

	@Test
	public void serverPic() throws IOException {

		System.out.println("server start...");

		// Create socket
		ServerSocket server = new ServerSocket(8899);

		// Blocking listening client
		Socket socket = server.accept();

		// Get the input stream
		InputStream in = socket.getInputStream();

		byte[] buf = new byte[1024];
		int len = 0;

		// Reading while writing
		// Write to server disk

		// Get the file output stream
		File file = new File("java.jpg");
		FileOutputStream out = new FileOutputStream(file);

		while ((len = in.read(buf)) != -1) {

			out.write(buf, 0, len);
		}

		System.out.println("Picture Acceptance Completed...");
		
		socket.shutdownInput();
		in.close();
		out.close();
		

	}

}

Client client sends pictures

package com.rrs.socketserver.client;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;

import org.junit.Test;

/**
 * @author lzx
 *
 */
public class ClientPic {

	@Test
	public void clientPic() throws IOException {

		System.out.println("client start...");

		// Create a socket client
		Socket client = new Socket("127.0.0.1", 8899);

		// Send a file from a local read file (read while write)

		// read file
		File file = new File("D:/Desktop/java.jpg");
		FileInputStream in = new FileInputStream(file);

		// Send 1k at a time
		byte[] buf = new byte[1024];

		int len = 0;

		OutputStream out = client.getOutputStream();

		while ((len = in.read(buf)) != -1) {
			out.write(buf, 0, len);
		}
		System.out.println("Picture Sending Completed...");

		out.close();
		in.close();
		client.shutdownOutput();

	}

}