Listening to a specific URL

[madness123]

Hi!

I have an assignment in which I need to create a program that would intercept that when a specific URL has been entered, it would load other contents instead of the content it currently has. For example if I were to load example.com and it would contain a string "Hello World", I will have to load it with "I did it!".

After investigating I found that the best approach for me would be to use a web proxy. However, I am only able to intercept localhost, and not external URLs.
I will appreciate any advice regarding catching when the correct URL has been entered.

Here is what I got so far:

public class ProxyServer {
	public static void main(String[] args) throws IOException {
		ServerSocket serverSocket = null;
		boolean listening = true;

		int port = 8118;
		serverSocket = new ServerSocket(port);
		System.out.println("Started on: " + port);

		while(listening){
			Thread t = new ProxyThread(serverSocket.accept());
			t.start();
		}
		
		serverSocket.close();
	}
}

public class ProxyThread extends Thread {
    private Socket socket = null;
    private static final int BUFFER_SIZE = 32768;
    
    public ProxyThread(Socket socket) {
        super("ProxyThread");
        this.socket = socket;
    }

    public void run() {
     
        try {
            DataOutputStream out = new DataOutputStream(socket.getOutputStream());
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            String inputLine, outputLine;
            int cnt = 0;
            String urlToCall = "";
       
            //begin get request from client
            while ((inputLine = in.readLine()) != null) {
                try {
                    StringTokenizer tok = new StringTokenizer(inputLine);
                    tok.nextToken();
                } catch (Exception e) {
                    break;
                }
                //parse the first line of the request to find the url
                if (cnt == 0) {
                    String[] tokens = inputLine.split(" ");
                    urlToCall = tokens[1];
                    System.out.println("Request for : " + urlToCall);
                }

                cnt++;
            }
            
            BufferedReader rd = null;
            try {
                
                URL url = new URL(urlToCall);
                URLConnection conn = url.openConnection();
             
                String line = "I did it!";
                
                InputStream is = null;
                is = new ByteArrayInputStream(line.getBytes(Charset.forName("UTF-8")));
                rd = new BufferedReader(new InputStreamReader(is));
                
                //send response to client
                byte by[] = new byte[ BUFFER_SIZE ];
                int index = is.read( by, 0, BUFFER_SIZE );
                while ( index != -1 )
                {
					out.write( by, 0, index );
					index = is.read( by, 0, BUFFER_SIZE );
                }
                out.flush();

            } catch (Exception e) {
                System.err.println("Encountered exception: " + e);
            }

            //close out all resources
            if (rd != null) {
                rd.close();
            }
            if (out != null) {
                out.close();
            }
            if (in != null) {
                in.close();
            }
            if (socket != null) {
                socket.close();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

[DarrylBurke]

All seems rather underhand to me. Why would you want to do this?

db