Help with a 14 line java proggie!! (Applet)

TenLeftFingers

I got this code from the JDK 1.4 tutorial. The server runs fine (now that I added exception handling), but the client always crashes. Any ideas?

import java.applet.*;
import java.awt.*;
import java.io.*;
import java.net.*;

public class ChatClientApplet extends Applet
{
  public void init() {
    String host = getParameter( "host" );
    int port = Integer.parseInt( getParameter( "port" ) );
    setLayout( new BorderLayout() );
    add( "Center", new ChatClient( host, port ) );
  }
}

the applet takes port address 5555 from the containing html file.

These are the run-time errors...

F:\BEDS\java\Murrough\JDK1.4_Turorial\jdk14tut\Chapter2>appletviewer client.html
java.security.AccessControlException: access denied (java.net.SocketPermission hostname resolve)
at java.security.AccessControlContext.checkPermission(AccessControlContext.java:270)
at java.security.AccessController.checkPermission(AccessController.java:401)
at java.lang.SecurityManager.checkPermission(SecurityManager.java:542)
at java.lang.SecurityManager.checkConnect(SecurityManager.java:1042)
at java.net.InetAddress.getAllByName0(InetAddress.java:937)
at java.net.InetAddress.getAllByName0(InetAddress.java:918)
at java.net.InetAddress.getAllByName(InetAddress.java:912)
at java.net.InetAddress.getByName(InetAddress.java:832)
at java.net.InetSocketAddress.<init>(InetSocketAddress.java:109)
at java.net.Socket.<init>(Socket.java:119)
at ChatClient.<init>(ChatClient.java:44)
at ChatClientApplet.init(ChatClientApplet.java:14)
at sun.applet.AppletPanel.run(AppletPanel.java:347)
at java.lang.Thread.run(Thread.java:536)


Regards,
merlin_bar

TenLeftFingers

Nevermind. I found another example in a different book and it works fine. Just needs modification.

brainstorm

im no expert but applets accessing file systems throw up errors like that a lot

seamus

Ya. Java was designed with security and modularity in mind - i.e. Applets are supposed to be self-providing, and have very little permission in way of accessing the computer they're running on.

merlin_bar - if you could post up your solution, or a summary of what you did to get it to work, would be handy if someone else arrived with the same problem

TenLeftFingers

If by file system access you mean the getParamater(String) method; I've always had problems with it.

I replaced it with

// make connection
         connection = new Socket( [b]getCodeBase().getHost()[/b], 5555 );

I've progressed a lot in the program so It's very messy at the moment, but it works. I should have it finished tonight, I'll post the whole feckin' lot then. Or a link to it perhaps!

Regards merlin_bar

TenLeftFingers

It runs fine with this code. (Both this class and the one in my first post are needed).

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import java.util.logging.Logger;
import java.util.Hashtable;

public class ChatClient extends Panel implements Runnable
{
	// Components for the visual display of the chat windows
	private TextField tf = new TextField();
	private TextArea ta = new TextArea();

	// The socket connecting us to the server
	private Socket socket;

	// The streams we communicate to the server; these come
	// from the socket
	private OutputStream out;
	private InputStream in;
	private boolean acceptID = true;

	private Hashtable codeTable;
	private Hashtable restoreTable;

	public void initRestoreTable(){
		restoreTable.put( ".-", "A");
		//just filled a load of morse code retrieval values
		restoreTable.put( "...-..-", "$");
	}
	public void initHashTable(){
		codeTable.put("A", ".-");
		//morse code entry values
		codeTable.put("$", "...-..-");

		Logger.global.info("Hashtable initialzed.");
	}

	public ChatClient( String host, int port ) {
		//set up hashtable
		codeTable = new Hashtable();
		restoreTable = new Hashtable();
		initHashTable();
		initRestoreTable();
		// Set up the screen
		setLayout( new BorderLayout() );
		add( "North", tf );
		add( "Center", ta );

		// We want to receive messages when someone types a line
		// and hits return, using an anonymous class as
		// a callback
		tf.addActionListener( new ActionListener() {
			public void actionPerformed( ActionEvent e ) {
				processMessage( e.getActionCommand() );
			}
		} );

		// Connect to the server
		try {
			// Initiate the connection
			socket = new Socket( host, port );
			// We got a connection!  Tell the world
			System.out.println( "connected to "+socket );
			// Let's grab the streams and create DataInput/Output streams
			// from them
			in = socket.getInputStream();
			out = socket.getOutputStream();
			// Start a background thread for receiving messages
			new Thread( this ).start();
		} catch( IOException ie ) { System.out.println( ie ); }
	}

	// Gets called when the user types something
	private void processMessage( String message ) {
		try {
			//Convert to morse code
			String morse = new String();   //To contain converted morse code.
			String indexedChar = new String();

			for ( int i = 0; i < message.length(); i++){
				indexedChar = "";
				indexedChar += message.charAt(i);
				morse += codeTable.get( indexedChar.toUpperCase() );
				morse += " ";
			}

			Logger.global.info(morse);

			// Send it to the server
			out.write( morse.getBytes() );//was message
			// Clear out text input field
			tf.setText( "" );
			morse = "";//LATEST
		} catch( IOException ie ) { System.out.println( ie ); }
	}

	//process recieved message, with header removed.
	private String revert(String rx){
		System.out.println("RX=>" +rx);
		String reverted = "";
		String tokens[];
		tokens = rx.split(" ");

		for ( int i = 0; i < tokens.length ; i++){
			tokens[i].concat(" ");
			reverted += (String)restoreTable.get(tokens[i]);
			Logger.global.info("Token[" +i +"] = " +tokens[i] +" returns " +reverted);
		}
		return reverted;
	}

	// Background thread runs this: show messages from other window
	public void run() {
		int myID;
		String myMorseID = "";
		String header = "";
		String message = "";
		String temp = "";
		try {

			byte buffer[] = new byte[4096];
			// Receive messages one-by-one, forever
			while (true) {
				//Accept ID from server
				if ( acceptID == true ){
					int r = in.read( buffer );
					String id = new String( buffer, 0, r );
					myID = (int)id.charAt(0);
					acceptID = false;
					myMorseID = String.valueOf(myID);
					myMorseID = (String) codeTable.get(myMorseID);
					Logger.global.info("myID: " +myID +". myMorseID: " +myMorseID);
					ta.append("Welcome user " +myID +"\n");
				}else{

					// Get the next message
					int r = in.read( buffer );
					message = new String( buffer, 0, r );

					//evaluate and condition String
					int headerBreak = message.indexOf(" ");

					try{
						if(message.length() > 0 && headerBreak != -1){
							header = message.substring(0, headerBreak);
							header = header.trim();
							Logger.global.info("HEADER " +header);



					if( header.equalsIgnoreCase(myMorseID) ){
						Logger.global.info("I have been addressed!");
						//remove header
						message = message.substring(headerBreak, message.length());
						message = message.trim();
						temp = revert(message);
							ta.append( temp+"\n" );
					}
					}
					}catch(Exception e){Logger.global.info("E");}
					message = "";
					header = "";
					temp ="";
				}
			}
		} catch( IOException ie ) { System.out.println( ie ); }
	}
}

Hope this helps. If anyone has a question, feel free to ask. Each client is given an ID on startup. If one client wants to chat to another (lets say 2 wants to talk to 3)...then 2 would type: "3_hello_there" (morse code doesn't support spaces)