2.3. TCP Socket Programming in Java

import java.io.*;
import java.net.*;

public class TCPClient {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 5000);
            OutputStream os = socket.getOutputStream();
            PrintWriter writer = new PrintWriter(os, true);
            writer.println("Hello Server");
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                socket.getInputStream()));
            System.out.println("Server says: " + reader.readLine());
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In this chunk, we look at the TCP Client code in Java. The client begins by creating a socket that connects to a server at a specified host and port (in this case, localhost and port 5000). It first obtains the output stream of the socket to send data to the server. The PrintWriter is used for writing a message to the server, in this case, 'Hello Server'. After sending the message, the client waits to read a response from the server. This is done through the input stream of the socket, allowing the client to receive and print a message from the server. Finally, it closes the socket connection to free resources.

Think of the TCP Client as a customer in a cafe. When the customer enters (creates a socket connection), they place an order (send a message). The cafe (server) prepares the order and serves it back (sends a response) before the customer leaves (closes the socket).

import java.io.*;
import java.net.*;

public class TCPServer {
    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(5000);
            System.out.println("Server is running...");
            Socket clientSocket = serverSocket.accept();
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                clientSocket.getInputStream()));
            System.out.println("Client says: " + reader.readLine());
            OutputStream os = clientSocket.getOutputStream();
            PrintWriter writer = new PrintWriter(os, true);
            writer.println("Hello Client");
            clientSocket.close();
            serverSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

This chunk describes the TCP Server code in Java. The server starts by creating a ServerSocket on port 5000 to listen for incoming client connections. When a client connects, the server accepts this connection, resulting in a new socket for the client (clientSocket). It reads a message sent from the client using a BufferedReader. After receiving the message, it then prepares to send a response to the client using an output stream and PrintWriter. Finally, the server closes both the client socket and the server socket, effectively ending the communication.

You can think of the TCP Server as a waiter in the same cafe. The waiter sets up a table (listens for connections). Once a customer arrives (client connects), the waiter takes their order (reads the client's message) and serves the meal (sends the server's response) before clearing the table (closing connections).

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