Working with proxy

I want to create a forward proxy .
And the requirement is that whenever browser hits a URL then that request should first go to that proxy, I want to add a header to this request then the modified request should go back to browser through which it will reach the remote server.

I tried to implement this through running a port on which I will read the request coming from browser .But I do not know how will I send the modified request back to the browser.

Please help me out!

Moved from Advanced Java

db

I have written the following code:

Code:

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


public class ProxyApp {

        public static void main(String a[]) throws IOException , Exception
        {
                ServerSocket proxySocket = new ServerSocket(7456);
                System.out.println("Socket created at port number.....7456.");
               

               
                System.out.println("waiting for browser to connect......");
               
                Socket browserSocket        = proxySocket.accept();
               
                System.out.println("request received from browser......");
               
               
                OutputStream browserOutputStream        = browserSocket.getOutputStream();
                InputStream browserInputStream                = browserSocket.getInputStream();
               
                byte[]      b = new byte[1];

                StringBuffer buf = new StringBuffer();
                String      s ;

                for ( ; ; ) {
                        int len ;

                        len = browserInputStream.read(b, 0, 1);
                        if ( len == -1 ) {
                                break ;
                        }
                        s = new String( b );
                        buf.append( s );
                        if ( b[0] != '\n' ) {
                                continue ;
                        }
                        break ;
                }

                String bufferedData = buf.toString();
                System.out.println("browser requested......"+bufferedData);
               

                int  start, end ;
               
                start = bufferedData.indexOf( ' ' ) + 1;
                while ( bufferedData.charAt(start) == ' ' ) {
                        start++ ;
                }
                end  = bufferedData.indexOf( ' ', start );
                String urlString = bufferedData.substring( start, end );

                System.out.println("browser requested..urlString...."+urlString);

               
                /*******************reading from server********************************/
                URL url = new URL(urlString);
        URLConnection connection = url.openConnection();
        connection.setDoOutput(true);

        OutputStream remoteOutputStream        =  connection.getOutputStream();
       
        System.out.println("sent to remote......"+bufferedData);
       
        remoteOutputStream.write(bufferedData.getBytes());
        remoteOutputStream.flush();
        remoteOutputStream.close();
       
        System.out.println("Data written to remote server...");
       
     
        InputStream remoteInputStream        = connection.getInputStream();

        byte[]      b1 = new byte[1];

                StringBuffer buf1 = new StringBuffer();
                String      s1 ;

                for ( ; ; ) {
                        int len ;

                        len = remoteInputStream.read(b1, 0, 1);
                        if ( len == -1 ) {
                                break ;
                        }
                        s1 = new String( b1 );
                        buf1.append( s1 );
                        if ( b1[0] != '\n' ) {
                                continue ;
                        }
                        break ;
                }

                String bufferedData1 = buf1.toString();
               
                System.out.println("Data read from remote server...bufferedData1..."+bufferedData1);
               
               
                browserOutputStream.write(bufferedData1.getBytes());
                browserOutputStream.flush();
                browserOutputStream.close();
               
                System.out.println("Data written to browser...");
                /**********************************************/


               

                System.out.println("**************END********************");
        }
}

---

But while getting the input stream from url connection I get Socket Exception.
Please tell me what is wrong...

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