A simple case

client:

package demo;

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

public class TCPClient {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("127.0.0.1", 7000);
        OutputStream out = socket.getOutputStream();
        out.write("hello".getBytes());
        InputStream in = socket.getInputStream();
        byte[] data = new byte[1024];
        int len = in.read(data);
        System.out.println(new String(data, 0, len));
        socket.close();
    }
}

Server side:

package demo;

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

public class TCPServer {
    public static void main(String[] args) throws IOException {
        ServerSocket server = new ServerSocket(7000);
        Socket socket = server.accept();
        InputStream in = socket.getInputStream();
        byte[] data = new byte[1024];
        int len = in.read(data);
        System.out.println(new String(data, 0, len));
        OutputStream out = socket.getOutputStream();
        out.write("Received".getBytes());
        socket.close();
        server.close();
    }
}

Start the server first, then the client. The server Prints: hello, then the client Prints: received

Pay attention to distinguish the flow objects here

Next, on the basis of this case, make a case of image upload

The essence of image upload is file copy

client:

package demo1;

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

public class TCPClient {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("127.0.0.1", 7000);
        OutputStream out = socket.getOutputStream();
        FileInputStream fis = new FileInputStream("d:\\666.jpeg");
        int len = 0;
        byte[] bytes = new byte[1024];
        while ((len = fis.read(bytes)) != -1) {
            out.write(bytes, 0, len);
        }
        socket.shutdownOutput();
        // Server side cannot read-1，Do not terminate. Call this method to terminate
        InputStream in = socket.getInputStream();
        len = in.read(bytes);
        System.out.println(new String(bytes, 0, len));
        fis.close();
        socket.close();
    }
}

Server side:

package demo1;

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 java.util.Random;

public class TCPServer {
    public static void main(String[] args) throws IOException {
        ServerSocket server = new ServerSocket(7000);
        Socket socket = server.accept();
        InputStream in = socket.getInputStream();
        File upload = new File("d:\\upload");
        if (!upload.exists()) {
            upload.mkdirs();
        }
        String filename = System.currentTimeMillis() + new Random().nextInt(999999) + ".jpeg";
        FileOutputStream fos = new FileOutputStream(upload + File.separator + filename);
        // Here is the problem of dealing with the duplicate names of pictures
        byte[] bytes = new byte[1024];
        int len = 0;
        while ((len = in.read(bytes)) != -1) {
            fos.write(bytes, 0, len);
        }
        socket.getOutputStream().write("Upload succeeded".getBytes());
        fos.close();
        socket.close();
        server.close();
    }
}

If multiple clients upload together, multi-threaded technology is needed, and each client takes up one thread

Client does not need to be modified

Server side:

package demo1;

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

public class TCPServer {
    public static void main(String[] args) throws IOException {
        ServerSocket server = new ServerSocket(7000);
        while (true) {
            Socket socket = server.accept();
            new Thread(new Upload(socket)).start();
        }
    }
}

package demo1;
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 java.util.Random;

public class Upload implements Runnable {

    private Socket socket;

    public Upload(Socket socket) {
        this.socket = socket;
    }

    public void run() {
        try {
            InputStream in = socket.getInputStream();
            File upload = new File("d:\\upload");
            if (!upload.exists()) {
                upload.mkdirs();
            }
            String filename = System.currentTimeMillis() + new Random().nextInt(999999) + ".jpeg";
            FileOutputStream fos = new FileOutputStream(upload + File.separator + filename);
            // Here is the problem of dealing with the duplicate names of pictures
            byte[] bytes = new byte[1024];
            int len = 0;
            while ((len = in.read(bytes)) != -1) {
                fos.write(bytes, 0, len);
            }
            socket.getOutputStream().write("Upload succeeded".getBytes());
            fos.close();
            socket.close();
        } catch (IOException ex) {
            System.out.println(ex);
        }
    }
}