client/server socket

does anyone know how to write the client/server program (using sockets) where the client can ask the server if the file does/does not exist; if it does then read the file contents from server and shows it...there must be two separate client and server windows

Hello Java_dude_101.

Welcome to the Java Programming Forums.

Firstly you should concentrate on getting a client to connect to the server. This code will help:

Writing the Server Side of a Socket (The Java™ Tutorials > Custom Networking > All About Sockets)

Play around with that. When you are happy, post the code you have and we will help you with the file part.

Thanks.

I was able to make the connection and send streams back and forth...here is an example of the client side. I chose to put the code for reading the entry in this actionListener since it was already performing that role.

Code Java:

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public Client(String host) {
        super("Client Window");
 
        chatServer = host; // set server to which this client connects
 
        enterField = new JTextField(); // create enterField
        enterField.setEditable(false);
        enterField.addActionListener(
                new ActionListener() {
                    // send message to server
 
                    public void actionPerformed(ActionEvent event) {
                        sendData(event.getActionCommand());
                        enterField.setText("");
 
 
                        try // display contents of file
                        {
                            // create Socket to make connection to server
 
                            messoutput = new Formatter(client.getOutputStream());
                            // messoutput.flush(); // flush output to send header information
                            messinput = new Scanner(client.getInputStream());
 
                            String fileName = event.getActionCommand() + "\n";
                            messoutput.format(fileName);
                            messoutput.flush(); // flush output
                            String inputLine = messinput.nextLine(); // read input line
                            displayArea.setText(inputLine); // show input line in textarea
 
                            // if file exists, display file contents
                            if (inputLine.equals("The file is:")) {
                                while (messinput.hasNextLine()) {
                                    inputLine = messinput.nextLine(); // read a new line
                                    displayArea.append('\n' + inputLine); // add line
                                } // end while
                            } // end if
                        } // end try
                        catch (IOException ioException) {
                            ioException.printStackTrace();
                            System.exit(1);
                        } // end catch
                        finally {
                            try {
                                input.close(); // close output
                                output.close(); // close input
                                client.close(); // close connection to server
                            } catch (IOException ioException) {
                                ioException.printStackTrace();
                                System.exit(1);
 
                            } // end method actionPerformed
                        } // end anonymous inner class
                    }
                }); // end call to addActionListener
//close the attempted file formatter scanner
        add(enterField, BorderLayout.NORTH);
 
        displayArea = new JTextArea(); // create displayArea
        add(new JScrollPane(displayArea), BorderLayout.CENTER);
 
        setSize(300, 150); // set size of window
        setVisible(true); // show window
    } // end Client constructor

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The server side...I have the get streams and process connections methods and I chose to use the process connection() for looking to see if the file actually there.

Code Java:

---

private void processConnection() throws IOException
   {
      String message = "Connection successful";
      sendData( message ); // send connection successful message
 
      // enable enterField so server user can send messages
      setTextFieldEditable( true );
 
      do // process messages sent from client
      {
         try // read message and display it
         {
            message = ( String ) input.readObject(); // read new message
            displayMessage( "\n" + message ); // display message
  //Attempted code to read format of entry and determine if it is a file
            //start code
         connection = server.accept(); // accept connection
         messoutput = new Formatter( connection.getOutputStream() );
         messoutput.flush(); // flush output to send header information
         messinput = new Scanner( connection.getInputStream() );
         File file = new File( messinput.nextLine() ); // get file name
         String result; // result from checking file
 
         // file does exist
         if ( file.exists() )
         {
            Scanner fileInput = new Scanner( file ); // file scanner
            messoutput.format( "The file is:\n" ); // write header
            messoutput.flush(); // flush output
 
            while ( fileInput.hasNextLine() )
            {
               result = fileInput.nextLine(); // read a line from file
               messoutput.format( "%s\n", result ); // output line of file
               messoutput.flush(); // flush output
            } // end while
         } // end if
         else // file does not exist
         {
            result = file.getName() + " does not exist\n";
            messoutput.format( result ); // write that file does not exist
            messoutput.flush(); // flush output
         } // end else
     // } // end try
         //end attempted code for reading format if entry
         } // end try
         catch ( ClassNotFoundException classNotFoundException )
         {
            displayMessage( "\nUnknown object type received" );
         } // end catch
 
      } while ( !message.equals( "CLIENT>>> TERMINATE" ) );
   } // end method processConnection

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