Use of servlet http tunneling for client server communication

Question

Hello I am having a problem connecting a simple client applet to a server application. I can connect the two directly using sockets. However, when I try to connect the two via a servlet the input stream cannot be accessed. The application is purely for demonstration. Here is some of the source code
A servlet for http tunneling
import java.io.*;
import java.net.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SocketServlet extends HttpServlet
     ServletInputStream servletinput;
     ServletOutputStream servletoutput;
     Socket socket;
     DataOutputStream dataoutput;
     DataInputStream datainput;     
     public SocketServlet()
public void init(ServletConfig servletconfig) throws ServletException
super.init(servletconfig);
log("Socket servlet initialized.");
     public void doPost( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException
try
servletinput = request.getInputStream();
socket = new Socket( InetAddress.getByName( "127.0.0.1" ), 5000 );
dataoutput = new DataOutputStream( socket.getOutputStream() );
try
                    byte[] inbytes = new byte[1024];
                    servletinput.read( inbytes );
                    String inmessage = new String( inbytes );                    
                    dataoutput.writeBytes( inmessage );
catch(IOException ioex)
dataoutput.flush();
datainput = new DataInputStream( socket.getInputStream() );
servletoutput = response.getOutputStream();
try
byte[] outbytes = new byte[1024];
datainput.read( outbytes );
servletoutput.write( outbytes );
catch(IOException ioex)
servletoutput.flush();
servletoutput.close();
catch(Exception ex)
// Server.java
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Server extends JFrame {
private JTextField enter;
private JTextArea display;
DataOutputStream output;
DataInputStream input;
public Server()
super( "Server" );
Container c = getContentPane();
     enter = new JTextField();
     enter.setEnabled( false );
     c.add( enter, BorderLayout.SOUTH );
display = new JTextArea();
c.add( new JScrollPane( display ),
BorderLayout.CENTER );
setSize( 300, 150 );
show();
public void runServer()
ServerSocket server;
Socket connection;
int counter = 1;
try {
// Step 1: Create a ServerSocket.
server = new ServerSocket( 5000, 100 );
while ( true ) {
// Step 2: Wait for a connection.
display.setText( "Waiting for connection\n" );
connection = server.accept();
display.append( "Connection " + counter +
" received from: " +
connection.getInetAddress().getHostName() );
// Step 3: Get input and output streams.
output = new DataOutputStream(
connection.getOutputStream() );
input = new DataInputStream(
connection.getInputStream() );
display.append( "\nGot I/O streams\n" );
// Step 4: Process connection.
String message =
"SERVER>>> Connection successful";
output.writeBytes( message );
enter.setEnabled( true );
               display.append( "\nConnected\n" );
do {
try {
                    byte[] mess = new byte[1024];
input.read( mess );
display.append( "\n" + message );
display.setCaretPosition(
display.getText().length() );
               catch (IOException ioex )
} while ( !message.equals( "CLIENT>>> TERMINATE" ) );
// Step 5: Close connection.
display.append( "\nUser terminated connection" );
enter.setEnabled( false );
output.close();
input.close();
connection.close();
++counter;
catch ( EOFException eof ) {
System.out.println( "Client terminated connection" );
catch ( IOException io ) {
io.printStackTrace();
private void sendData( String s )
try {
output.writeBytes( "SERVER>>> " + s );
display.append( "\nSERVER>>>" + s );
catch ( IOException cnfex ) {
display.append(
"\nError writing object" );
public static void main( String args[] )
Server app = new Server();
app.addWindowListener(
new WindowAdapter() {
public void windowClosing( WindowEvent e )
System.exit( 0 );
app.runServer();
// Fig. 21.4: Client.java
// Set up a Client that will read information sent
// from a Server and display the information.
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.util.zip.*;
public class Client extends Applet implements ActionListener {
private TextField enter;
private TextArea display;
DataOutputStream output;
DataInputStream input;
private Button button, button2;
URLConnection connection;
private byte[] bytes1, bytes2;
private String message, message2;
public void init()
setLayout( new BorderLayout() );
enter = new TextField( " Enter text here " );
enter.setEnabled( false );
enter.addActionListener( this );
add( enter, BorderLayout.NORTH );
display = new TextArea( 4, 30 );
     display.setEditable( false );
add( display, BorderLayout.CENTER );
     button = new Button( "Connect" );
     button.addActionListener( this );
     add( button, BorderLayout.SOUTH );
public void runClient()
Socket client;
try {
// Step 1: Create a Socket to make connection.
display.setText( "Attempting connection\n" );
          URL currentpage = getCodeBase();
          String protocol = currentpage.getProtocol();
          String host = currentpage.getHost();
          int port = 8100;
          String urlsuffix = "/servlet/SocketServlet";
          URL dataurl = new URL( "http://localhost:8100/servlet/SocketServlet" );
          connection = dataurl.openConnection();
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setRequestProperty("Content-type", "application/octet-stream");
          connection.setUseCaches( false );
          display.append( "\nConnected to: " + host );          
// Step 2: Get the output streams.
output = new DataOutputStream(
connection.getOutputStream() );
          display.append( "\n got output stream\n" );
          // Step 3 get input connection
          try
          display.append( "\nAttempting to connect to input stream\n" );
               input = new DataInputStream( connection.getInputStream() );
               bytes1 = new byte[1024];
               input.readFully( bytes1 );
               display.append( "\nGot input stream\n" );
               message = new String( bytes1 );
               display.append( "\n" + message + "\n" );          
          catch ( IOException ioex )
          // Step 3: Process connection.
          enter.setEnabled( true );
          do {
          try {
bytes2 = new byte[1024];
          input.readFully( bytes2 );
          message2 = new String( bytes2 );
          display.append( "\n" + message2 );
          display.setCaretPosition(
          display.getText().length() );
          catch ( IOException ioex ) {
          display.append(
          "\nUnknown object type received" );
          } while ( !message.equals( "SERVER>>> TERMINATE" ) );
// Step 4: Close connection.
display.append( "Closing connection.\n" );
output.close();
input.close();
     catch (MalformedURLException mfe )
catch ( EOFException eof ) {
System.out.println( "Server terminated connection" );
catch ( IOException e ) {
e.printStackTrace();
private void sendData( String s )
try {
message = s;
output.writeBytes( "CLIENT>>> " + s );
display.append( "\nCLIENT>>>" + s );
catch ( IOException cnfex ) {
display.append(
"\nError writing object" );
public void actionPerformed( ActionEvent e )
     if ( e.getActionCommand() == "Connect" )
          runClient();
     else
          sendData( e.getActionCommand() );
public static void main(String args[])
Frame f = new Frame("Chat Client");
     Client c = new Client();
     c.init();
     f.add("Center", c);
     f.setSize(300, 150);
     f.show();
the connection appears to fail at client step 3, any help is super, thanks
Aidan

Answer 1

Hi,
In your client you are trying to open OutputStream even though you are not using it.
So there are two solutions here.
1. If you dont need OutputStream your code shoud look like this
try {
// Step 1: Create a Socket to make connection.
display.setText( "Attempting connection\n" );
URL currentpage = getCodeBase();
String protocol = currentpage.getProtocol();
String host = currentpage.getHost();
int port = 8100;
String urlsuffix = "/servlet/SocketServlet";
URL dataurl = new URL( "http://localhost:8100/servlet/SocketServlet" );
connection = dataurl.openConnection();
//connection.setDoOutput(true);
connection.setDoInput(true);
connection.setRequestProperty("Content-type", "application/octet-stream");
connection.setUseCaches( false );
display.append( "\nConnected to: " + host );
// Step 2: Get the output streams.
//output = new DataOutputStream(
//connection.getOutputStream() );
//display.append( "\n got output stream\n" );
display.append( "\n Not interested in output stream\n" );
//Step 3 Inpustream related
// Step 4: Close connection.
display.append( "Closing connection.\n" );
//output.close();
input.close();
1. If you need OutputStream, close your OutputStream before even trying to get InputStream, your code should like this
try {
// Step 1: Create a Socket to make connection.
display.setText( "Attempting connection\n" );
URL currentpage = getCodeBase();
String protocol = currentpage.getProtocol();
String host = currentpage.getHost();
int port = 8100;
String urlsuffix = "/servlet/SocketServlet";
URL dataurl = new URL( "http://localhost:8100/servlet/SocketServlet" );
connection = dataurl.openConnection();
//connection.setDoOutput(true);
connection.setDoInput(true);
connection.setRequestProperty("Content-type", "application/octet-stream");
connection.setUseCaches( false );
display.append( "\nConnected to: " + host );
// Step 2: Get the output streams.
output = new DataOutputStream(
connection.getOutputStream() );
display.append( "\n got output stream\n" );
//I'll do whateve I've to do with outputstream
//done with output stream closing
output.close();
//Step 3 Inpustream related
// Step 4: Close connection.
display.append( "Closing connection.\n" );
//output.close();
input.close();
hope this works
all the best,
Raj