Hello,
I am creating a client/server application that verifies math equations for addition, subtraction, and division. I think I just need someone else’s eyes to possibly see where I am going wrong with this. Everything seems to be working fine except for one variable. This is the String serverAnswer variable in my Server class. When I debug the application, the serverAnswer variable remains null, can anyone tell me what I’m doing wrong? I wrote the code for where it should be populated in the processConnection() method of my server class. I know this is a lot of code, but it is needed to debug the application. Thank you.
import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.lang.*;
import sun.io.Converters;
import javax.script.*;
public class Server extends JFrame
{
private JTextField enterField; // inputs message from user
private JTextArea displayArea; // display information to user
private ObjectOutputStream output; // output stream to client
private ObjectInputStream input; // input stream from client
private ServerSocket server; // server socket
private Socket connection; // connection to client
private int counter = 1; // counter of number of connections
String serverAnswer;
//private String serverAnswer;
// set up GUI
public Server()
{
super( "Server" );
enterField = new JTextField(); // create enterField
enterField.setEditable( false );
enterField.addActionListener(
new ActionListener()
{
// send message to client
public void actionPerformed( ActionEvent event )
{
sendData( event.getActionCommand() );
enterField.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
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 Server constructor
// set up and run server
public void runServer()
{
try // set up server to receive connections; process connections
{
server = new ServerSocket( 12345, 100 ); // create ServerSocket
while ( true )
{
try
{
waitForConnection(); // wait for a connection
getStreams(); // get input & output streams
processConnection(); // process connection
} // end try
catch ( EOFException eofException )
{
displayMessage( "\nServer terminated connection" );
} // end catch
finally
{
closeConnection(); // close connection
counter++;
} // end finally
} // end while
} // end try
catch ( IOException ioException )
{
ioException.printStackTrace();
} // end catch
} // end method runServer
// wait for connection to arrive, then display connection info
private void waitForConnection() throws IOException
{
displayMessage( "Waiting for connection\n" );
connection = server.accept(); // allow server to accept connection
displayMessage( "Connection " + counter + " received from: " +
connection.getInetAddress().getHostName() );
} // end method waitForConnection
// get streams to send and receive data
private void getStreams() throws IOException
{
// set up output stream for objects
output = new ObjectOutputStream( connection.getOutputStream() );
output.flush(); // flush output buffer to send header information
// set up input stream for objects
input = new ObjectInputStream( connection.getInputStream() );
displayMessage( "\nGot I/O streams\n" );
} // end method getStreams
// process connection with client
private void processConnection() throws IOException
{
String message = "Connection successful";
sendData( message ); // send connection successful message
// enable enterField so server user can send messages
setTextFieldEditable( false );
ScriptEngine engine = new ScriptEngineManager().getEngineByExtension("js");
do // process messages sent from client
{
try // read message and display it
{
message = ( String ) input.readObject(); // read new message
if (message.contains("+")){
Object result = engine.eval(message);
serverAnswer = String.valueOf(result);
}
else if(message.contains("/")){
Object result = engine.eval(message);
serverAnswer = String.valueOf(result);
}
else if(message.contains("-")){
Object result = engine.eval(message);
serverAnswer = String.valueOf(result);
}
else if (message.equals(serverAnswer)){
displayMessage("\n" + "You are correct");
}
else{
displayMessage("\n" + "Incorrect!");
}
//displayMessage("\n" + serverAnswer);
}
catch (ScriptException e) {
// Something went wrong
e.printStackTrace();
}
catch (ClassNotFoundException classNotFoundException){
displayMessage ( "\nUnknown object type received" );
}
displayMessage( "\n" + message ); // display message
} // end try
/* catch ( ClassNotFoundException classNotFoundException )
{
displayMessage( "\nUnknown object type received" );
} // end catch
} */while ( !message.equals( "CLIENT>>> TERMINATE" ) );
} // end method processConnection
// close streams and socket
private void closeConnection()
{
displayMessage( "\nTerminating connection\n" );
setTextFieldEditable( false ); // disable enterField
try
{
output.close(); // close output stream
input.close(); // close input stream
connection.close(); // close socket
} // end try
catch ( IOException ioException )
{
ioException.printStackTrace();
} // end catch
} // end method closeConnection
// send message to client
private void sendData( String message )
{
try // send object to client
{
output.writeObject( "SERVER>>> " + message );
output.flush(); // flush output to client
displayMessage( "\nSERVER>>> " + message );
} // end try
catch ( IOException ioException )
{
displayArea.append( "\nError writing object" );
} // end catch
} // end method sendData
// manipulates displayArea in the event-dispatch thread
private void displayMessage( final String messageToDisplay )
{
SwingUtilities.invokeLater(
new Runnable()
{
public void run() // updates displayArea
{
displayArea.append( messageToDisplay ); // append message
} // end method run
} // end anonymous inner class
); // end call to SwingUtilities.invokeLater
} // end method displayMessage
// manipulates enterField in the event-dispatch thread
private void setTextFieldEditable( final boolean editable )
{
SwingUtilities.invokeLater(
new Runnable()
{
public void run() // sets enterField's editability
{
enterField.setEditable( editable );
} // end method run
} // end inner class
); // end call to SwingUtilities.invokeLater
} // end method setTextFieldEditable
} // end class Serverimport javax.swing.JFrame;
public class ServerTest
{
public static void main( String args[] )
{
Server application = new Server(); // create server
application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
application.runServer(); // run server application
} // end main
} // end class ServerTestimport java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.JLabel;
public class Client extends JFrame
{
private JTextField equationField; // enter equation here
private JTextField answerField;//enter answer here
private JTextArea displayArea; // display information to user
private ObjectOutputStream output; // output stream to server
private ObjectInputStream input; // input stream from server
private String message = ""; // message from server
private String chatServer; // host server for this application
private Socket client; // socket to communicate with server
private JLabel label;//direction label
// initialize chatServer and set up GUI
public Client( String host )
{
super( "Client" );
chatServer = host; // set server to which this client connects
/*
label = new JLabel("Enter equation above and answer below.");//create label
add (label, BorderLayout.NORTH);
*/
equationField = new JTextField(); // create enterField
equationField.setEditable( false );
equationField.addActionListener(
new ActionListener()
{
// send message to server
public void actionPerformed( ActionEvent event )
{
sendData( event.getActionCommand() );
equationField.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
add( equationField, BorderLayout.NORTH);
answerField = new JTextField(); // create enterField
answerField.setEditable( false );
answerField.addActionListener(
new ActionListener()
{
// send message to server
public void actionPerformed( ActionEvent event )
{
sendData( event.getActionCommand() );
answerField.setText( "" );
} // end method actionPerformed
} // end anonymous inner class
); // end call to addActionListener
add( answerField, BorderLayout.SOUTH );
displayArea = new JTextArea(); // create displayArea
add( new JScrollPane( displayArea ), BorderLayout.CENTER);
setSize( 500, 250 ); // set size of window
setVisible( true ); // show window
} // end Client constructor
// connect to server and process messages from server
public void runClient()
{
try // connect to server, get streams, process connection
{
connectToServer(); // create a Socket to make connection
getStreams(); // get the input and output streams
processConnection(); // process connection
} // end try
catch ( EOFException eofException )
{
displayMessage( "\nClient terminated connection" );
} // end catch
catch ( IOException ioException )
{
ioException.printStackTrace();
} // end catch
finally
{
closeConnection(); // close connection
} // end finally
} // end method runClient
// connect to server
private void connectToServer() throws IOException
{
displayMessage( "Attempting connection\n" );
// create Socket to make connection to server
client = new Socket( InetAddress.getByName( chatServer ), 12345 );
displayMessage("Enter equation in top field and answer in the bottom field\n");
// display connection information
displayMessage( "Connected to: " +
client.getInetAddress().getHostName() );
} // end method connectToServer
// get streams to send and receive data
private void getStreams() throws IOException
{
// set up output stream for objects
output = new ObjectOutputStream( client.getOutputStream() );
output.flush(); // flush output buffer to send header information
// set up input stream for objects
input = new ObjectInputStream( client.getInputStream() );
displayMessage( "\nGot I/O streams\n" );
} // end method getStreams
// process connection with server
private void processConnection() throws IOException
{
// enable enterField so client user can send messages
setTextFieldEditable( true );
do // process messages sent from server
{
try // read message and display it
{
message = ( String ) input.readObject(); // read new message
displayMessage( "\n" + message ); // display message
} // end try
catch ( ClassNotFoundException classNotFoundException )
{
displayMessage( "\nUnknown object type received" );
} // end catch
} while ( !message.equals( "SERVER>>> TERMINATE" ) );
} // end method processConnection
// close streams and socket
private void closeConnection()
{
displayMessage( "\nClosing connection" );
setTextFieldEditable( false ); // disable enterField
try
{
output.close(); // close output stream
input.close(); // close input stream
client.close(); // close socket
} // end try
catch ( IOException ioException )
{
ioException.printStackTrace();
} // end catch
} // end method closeConnection
// send message to server
private void sendData( String message )
{
try // send object to server
{
output.writeObject( "CLIENT>>> " + message );
output.flush(); // flush data to output
displayMessage( "\nCLIENT>>> " + message );
} // end try
catch ( IOException ioException )
{
displayArea.append( "\nError writing object" );
} // end catch
} // end method sendData
// manipulates displayArea in the event-dispatch thread
private void displayMessage( final String messageToDisplay )
{
SwingUtilities.invokeLater(
new Runnable()
{
public void run() // updates displayArea
{
displayArea.append( messageToDisplay );
} // end method run
} // end anonymous inner class
); // end call to SwingUtilities.invokeLater
} // end method displayMessage
// manipulates enterField in the event-dispatch thread
private void setTextFieldEditable( final boolean editable )
{
SwingUtilities.invokeLater(
new Runnable()
{
public void run() // sets enterField's editability
{
equationField.setEditable( editable );
answerField.setEditable(editable);
} // end method run
} // end anonymous inner class
); // end call to SwingUtilities.invokeLater
} // end method setTextFieldEditable
} // end class Clientimport javax.swing.JFrame;
public class ClientTest
{
public static void main( String args[] )
{
Client application; // declare client application
// if no command line args
if ( args.length == 0 )
application = new Client( "127.0.0.1" ); // connect to localhost
else
application = new Client( args[ 0 ] ); // use args to connect
application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
application.runClient(); // run client application
} // end main
} // end class ClientTest