Browsers, OLE, DDE, SDI, CCI, NEO...

How do I have my applet send the browser to a new location?

(Submitted by Cliff Berg)

Normal Java way:
String url = new URL("http://www.digitalfocus.com");
applet.showDocument(url, "MY_NETSCAPE_FRAME");

Unfortunately, in Netscape 2 and Netscape 3 beta 4 this does not work if the
user leaves the applet page - even if you have a Java frame still visible.

Workaround using Netscape 3 Javascript:
import netscape.javascript.*;

JSObject win = JSObject.getWindow(applet);
String url = new URL("http://www.digitalfocus.com");
win.eval("open(\"" + url + "\",\"" + "MY_NETSCAPE_FRAME" + "\")");

(Submitted by Jeff Breidenbach)

You may use
getAppletContext().showDocument(newplace);
where newplace is the URL you want the browser to go to.

(Submitted by William S. Clark)

/*** Load URL.*/
public boolean loadUrl() {
	urlLoaded = true;		// well, tried to load anyway
	if (url == null)
	return false;
	dbg("loadUrl()");      
	// use showDocument() to display new URL.
	// Note: Netscape 2.0b2 problems here... I don't really understand how
	// to catch errors from showDocument()!
	try {
		getAppletContext().showDocument(url);
	}
	catch (Exception e) {
		if (url.getRef() == null) {
			errMessage = "Couldn't load url. Try to re-start Netscape :-(";
		}
		else {
			errMessage = "Couldn't load url: " + url.getRef();
		}
		return false;
	}
	return true;
}

How do I send an http server a request for an object, and have it pass the content back to the browser to process it like an html (or any other kind of) page?

(Submitted by Daryoush Mehrtash)

Here is the code segment that worked for me:

// Open the URL and display it as a new page
try {
    String NLinkname = "http://home.netscape.com";
    URL NLink = new URL(NLinkname);
    MYAPPLET.getAppletContext().showDocument(NLink);
}
catch(java.net.MalformedURLException e) {
    System.out.println("Malformed URL!!!! exception"); 
}

How can applets on the same page communicate?

(Submitted by Seokkyu Kong)

There are two solution on this problem. One is as

Applet1:

import java.awt.*;
import java.applet.*;

public class Applet1 extends java.applet.Applet{
  public boolean handleEvent(Event evt){
    Applet buddy=(Applet)getAppletContext().getApplet("buddy");
    return (buddy!=null) ? buddy.handleEvent(evt):false;
  }
}

Applet2:

import java.awt.*;
public class Applet2 extends java.applet.Applet{
  String str="";
  public boolean handleEvent(Event evt){
    str=evt.toString();
    repaint();
    return true;
  }
  public void paint(Graphics g){
    g.drawString(str, 0, size().height * 2 / 3);
  }
}

and

test1.html:

<html>
<head>Test</head>
<body>
  <applet code = Applet1.class width=100 height=100></applet>
  <applet code = Applet2.class width=400 height=30 name=buddy></applet>
</body>
</html>

Another solution is

Applet3:

import java.awt.*;
import java.applet.*;

class Applet2 extends Applet{
  public boolean handleEvent(Event evt){
  return true;
  }
}

public class Applet3 extends java.applet.Applet{
  public boolean handleEvent(Event evt){
    Applet2 buddy=(Applet2)getAppletContext().getApplet("buddy");
    return (buddy != null) ? buddy.handleEvent(evt):false;
  }
}

and Applet2 is same above,

test2.html:

<html>
<head>Test</head>
<body>
  <applet code = Applet3.class width=100 height=100></applet>
  <applet code = Applet2.class width=400 height=30 name=buddy></applet>
</body>
</html>

(Submitted by Bill Giel)

/* Very simple inter-applet communication demo
 * for any number of applets.
 * by Bill Giel, rvdi@usa.nai.net
 *               http://www.nai.net/~rvdi/home.htm
 *
 *
 *  <HTML>
 *  <HEAD><TITLE>Inter-Applet Test</TITLE></HEAD>
 *  <BODY>
 *  <applet code="interapp.class" height=100 width=100></applet>
 *  <applet code="interapp.class" height=100 width=100></applet>
 *  <applet code="interapp.class" height=100 width=100></applet>
 *
 *  </BODY>
 *  </HTML>
 *
 * This example uses three applets of the same class, but the
 * technique could be applied to different applets that shared
 * a common class containing static members to share data among
 * the different applets.
 *
 */


import java.awt.*;
import java.applet.*;

public class interapp extends Applet implements Runnable
{
    /////////////////////////////////////////////
    // Static members are common in value to all
    // instances.
    /////////////////////////////////////////////
    static final String BUTTON="Hit me!";
    
    static String globalName = null;
    static boolean globalHitFlag=false;
    static int counter = 0;

    /////////////////////////////////////
    // These are unique in value for each
    // instance.
    /////////////////////////////////////
    String instanceName=null;
    boolean instanceHitFlag=false;
    int width,height;
    Thread appThread=null;

    public void init()
    {
        Button button;
        
        instanceName=new String("Hit on No. " + (counter + 1));
        counter++;
	add (button=new Button(BUTTON));
	width=size().width; height=size().height;
        button.move((width-button.size().width)/2,
                            (width-button.size().width)/2);
    }

    public boolean action(Event evt, Object arg)
    {
	if(arg.equals(BUTTON)){
	    globalName=instanceName;
	    globalHitFlag=!globalHitFlag;
	    return true;
        }
	else return false;  
    }

    public void paint(Graphics g)
    {
	if(null != globalName){
    	    FontMetrics fm=g.getFontMetrics();
	    int yPos=height/2;
	    int xPos=(width-fm.stringWidth(globalName))/2;
	    
            g.drawString(   globalName,xPos,yPos);
	}
    }

    public void run()
    {
        Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
        for(;;)
            ////////////////////////////////////////
            // If the instance data no longer equals
            // the global data, then there was a hit.
            /////////////////////////////////////////
            if(instanceHitFlag != globalHitFlag){
                repaint();
                instanceHitFlag=globalHitFlag;
            }
    }
    
    public void start()
    {
        if(appThread == null){
            appThread = new Thread(this);
            appThread.start();
        }
    }

    public void stop()
    {
        appThread.stop();
        appThread=null;
    }	
}

(Submitted by Albert M. Lopez)

In this example, Applet1 gets text from an textBox and then calls the appendText function of Applet2. Applet2 appends the text to a textArea box.

// Applet1
import java.awt.*;
 
 public class Applet1 extends java.applet.Applet {

        TextField inputText;
        Panel myPanel;

        public void init() {

                resize( 100, 100 );

                setLayout(new BorderLayout());

                add("South", myPanel = new Panel() );

                GridBagLayout gridBag = new GridBagLayout();
                GridBagConstraints con = new GridBagConstraints();
                myPanel.setLayout( gridBag );

                inputText = new TextField( "", 15 );
                inputText.setEditable( true );
                con.gridwidth = GridBagConstraints.REMAINDER; // end of row 
                gridBag.setConstraints( inputText, con ); // end of row 
                myPanel.add( inputText );

                con.gridwidth = 1;
                Button enterText = new Button( "Enter Text" );
                myPanel.add ( enterText );
                myPanel.enable();

        }


        public boolean action(Event ev, Object arg) { 

                if( ev.target instanceof Button)  
                { 

                        String textMsg = inputText.getText().trim();
                        Applet2 applet2 = (Applet2)getAppletContext().getApplet("applet2");

                        if ( applet2 != null )
                        {
                                applet2.AppendText( textMsg );
                                return true;
                        }

                        else
                                return false;

                }

                return false;
        }



//Applet2
import java.awt.*;

public class Applet2 extends java.applet.Applet {

        TextArea textBox;
        Panel myPanel;

        public void init() {

                resize ( 100, 100 );

                setLayout(new BorderLayout());

                add("South", myPanel = new Panel() );


                textBox = new TextArea( 5, 40 );
                myPanel.add( textBox );
                myPanel.enable();

        }


        public void AppendText( String msg )

        {
                String newLine = new String( "\n" );
                textBox.appendText( msg );
                textBox.appendText( newLine );


        }

}

(Submitted by Matt Young)

From Lemay & Perkins, p. 298:

for( Enumeration e = getAppletContext().getApplets(); e.hasMoreElements();) {
    Applet current = (Applet)(e.nextElement());
    f(current);
}

where f is a function call.

(Submitted by Friedhelm Ries)

Quoting elharo@sunsite.unc.edu (in his comp.lang.java.faq) http://sunsite.unc.edu/javafaq/javafaq.html:
"At this point in time applets may communicate with other applets on the same page. As yet there is no way for applets on different pages to communicate directly. This may be added at some point in the future."

For applets on the same page Arthur van Hoff has provided this example:
Applet 1:

    import java.awt.*;
    public class Applet1 extends java.applet.Applet {
        public boolean handleEvent(Event evt) {
            Applet2 buddy = (Applet2)getAppletContext().getApplet("buddy");
            return (buddy != null) ? buddy.handleEvent(evt) : false;
        }
    }

Applet 2:

    import java.awt.*;
    public class Applet2 extends java.applet.Applet {
        String str = "";
        public boolean handleEvent(Event evt) {
            str = evt.toString();
            repaint();
            return true;
        }
        public void paint(Graphics g) {
            g.drawString(str, 0, size().height * 2 / 3);
        }
    }

HTML:

<HTML>
<HEAD>
</HEAD>
<BODY>
    <applet code=Applet1.class width=100 height=100></applet>
    <applet code=Applet2.class width=400 height=30 name=buddy></applet>
</BODY>
</HTML>
It is conceivable to have applets that talk to a server somewhere on the Internet and store any data that needs to be serialized there. Then, when another applet needs this data, it could connect to this same server. Implementing this is non-trivial. However there is currently no secure way to store this data on the client.

How do I retrieve an HTML page and extract (parse) out only the data I need to use?

(Submitted by Peter Ott)

/* code snippet to grab a page from the httpd server
 * and parse the returned info.  
*/

...

/* build the URL */
String tmpURL = new String("http://www.foo.bar/junk.html");
URL infoLink = new URL(tmpURL);

/* start the connection with the httpd and talk */
InputStream serverIO = infoLink.openStream();
/* the stream doesn't need to be buffered, but
 * it's what I used during testing */
BufferedInputStream bufServerIO = new BufferedInputStream(serverIO);

/* init the buffer that'll hold the info coming from the server */
StringBuffer oneLink = new StringBuffer();

/* setup some parsing variables */
int info;
char histchar1=' ',histchar2=' ';

/* do the deed - one character at a time.
 * you can use read(byte b[], int off, int len) if you know
 * how many characters you expect from the server.
*/
while((info=bufServerIO.read())!=-1)
{
  oneLink.append((char)info); /* make note of the info */

  /* Sample Parsing: Now I look for the "/UL" string
   * parsing this way is ALOT faster than using oneLink.toString().indexOf("/UL")
   */	
  if(((char)info=='L')&&(histchar1=='U')&&
     (histchar2=='/'))
    {
      /* do stuff with oneLink */
    }
  histchar2=histchar1;
  histchar1=(char)info;
}

...

How do I design an applet to run in both a browser and as a standalone application?

(Submitted by Vivek Pabby)

// The following class would run as an application/applet. Use the // supplied HTML file to run as an applet.

import java.awt.*;
import java.applet.*;

public class easyOne extends Applet 
{
        public void init() {
        }
        public void resize() {
                resize(300,300);
        }
	public easyOne() {
		setLayout(new BorderLayout());
		Panel p1 = new Panel();
		p1.setLayout(new FlowLayout());
		add("South", p1);
 		p1.add(new Button("ButtonOne"));	 
		p1.add(new Button("AnotherButton"));	 
	}

	public void paint(Graphics g) {
		g.setColor(Color.cyan);
		g.drawRect(10,10,150,150);
		g.fillRect(10,10,150,150);
	}

	public static void main(String args[]) {
		Frame f1 = new Frame("Standalone Application");
		easyOne s1 = new easyOne();
	    f1.add("Center", s1);
	    f1.resize(300, 300);
	    f1.show();	
		s1.init();
		s1.start();
	}
}

How do I specify an applet that resides on a remote machine?

(Submitted by Steve Alexander)

The way to point to java applets which are located on a different server is to use the "CODEBASE" parameter in the applet html. It seems you cannot explicitly list the URL of the java applet in the CODE parameter but you CAN list a URL in the CODEBASE parameter. So....
	applet code="MyJavaApplet.class"
        width = 300
        height = 300
		CODEBASE="http://www.mydomain.fun/appletdirectory/"
is the correct html syntax to go to a different server (the one listed on the CODEBASE parameter) and get the applet listed on the CODE parameter.

How do I display HTML generated by an applet?

(Submitted by Cliff Berg)

String myHTML = new String(
   "javascript:'<title>My Page</title><h1>My Page</h1>'");
getAppletContext().showDocument(new URL(myHTML));

How do I keep an applet running as the user moves away from the page that launched my applet?

(Submitted by David J. Bianco)

When your browser moves on to a different page, it will generally call your applet's stop() method. If you override the default, you can keep your applet running "in the background" while Netscape does other things. Adding the following to your class will probably do what you want:
    public void stop() {
        return;
    }
As you can see, the stop() method doesn't actually do anything. It just overrides the default so that Netscape (or whatever) can't use it to stop your applet.
This method is especially useful if your applet floats in it's own frame. Note that this means you must provide your users with some other way to kill off your applet. Also note that if your applet displays inline (ie. not in it's own frame), and the user goes off and does other stuff with Netscape, your applet will still be running, taking valuable CPU time.
Be careful overriding the stop() method.

What information can I get about the current applet context? How do I get the current location of the browser?

(Submitted by the editor)

Use Applet.getAppletContext(), Applet.getCodeBase(), and Applet.getDocumentBase().

How do I get the current HTML content? the Bookmarks the user saved? the Go list? the current browser font?

How do I get the current location of the browser? the current HTML content? the Bookmarks the user saved? the Go list? the current browser font?

How would one go about writing the specialized classes necessary in Java to support reading and writing Annotation files such as Mosaic creates?

How do I get Netscape2.0 on a PC to go to a page that does have Java applet on it and Netscape2.0 on a Mac witch does not have java to stay on the fisrt page?

(Submitted by Eric A. Zarko)

The best way to do this is on the server, with a CGI script. For instance:
#!/usr/local/bin/perl

use CGI;                     # CGI.pm See note below
$cgi = new CGI;

if(scalar(grep(/Macintosh/, $ENV{HTTP_USER_AGENT})) > 0) {
  # Give them the no applet page
  print $cgi->redirect('no-applet.html');
} else {
  # Give them the applet page
  print $cgi->redirect('applet.html');
}
exit(0);
This is assuming you have perl and the CGI.pm module by Lincoln Stein. If you do not, get perl at: ftp://ftp.netlabs.com/pub/outgoing/perl5.0/ and get CGI.pm at: http://www-genome.wi.mit.edu/ftp/pub/software/WWW/.

(Submitted by Cliff Berg)

Any HTML that appears between the applet tag and the end-applet tag is executed if the browser does not support applets. Thus, this non-Java HTML can provide whatever content is intended for a non-Java browser. The applet can, on the other hand, immediately do a getAppletContext().showDocument(url), causing the browser to go to another page without delay.

How can I programmatically access an applet from JavaScript within the Netscape Navigator browser?

(Submitted by Cliff Berg)

Adapted from Netscape's own Javascript help files:

<APPLET CODE="colors.class" WIDTH=1000 HEIGHT=60 NAME="colorApp" MAYSCRIPT>
</APPLET>

<FORM NAME=colorText>

<INPUT TYPE="text" NAME="textBox" LENGTH=50>

<INPUT TYPE="button" VALUE="Change Text"
 onClick="document.colorApp.setString(document.colorText.textBox.value)">

<P><INPUT TYPE="button" VALUE="Restart"
 onClick="document.colorApp.start()">

</FORM>

How do I show a document in one Netscape frame under the control of an applet running in another frame? and do this repeatedly?

(Submitted by Hoa Ton-That)

You want to create the second frame with a name. ie:

<frame
    name="control"
    src="applet.html"
>
<frame
  name=applet frame target"
  src=""
>

Then you would use the following code:

void moveFrame(String dest) {
  URL destURL=null;

  try {
    destURL = new URL(dest);
  } catch (MalformedURLException mal){
  }

  getAppletContext().showDocument(destURL,"target");
}

How do you make an applet that only runs in the background, i.e. has no area on the HTML page to paint?

(Submitted by E. Will Brown)

In the applet tag, set height=0 width=0.

Here is an example that puts scrolling text in the status bar but doesn't draw anything on the page itself. This works (netscape 2.0 Solaris 2.4) but isn't very pretty.

/* ScrollStatus.java                         emacs C++ mode: -*- C++ -*-
 
Optional parameters: message, width
Default values:
        message = " Isn't scrolling text in the status line annoying? "
        width = 36
 
Example usage:
 
<applet codebase=ScrollStatus code=ScrollStatus.class width=0 height=0>
<param name="message" value="Hello World!">
<param name="width" value="24">
</applet>
 
*/
 
import java.util.*;
import java.applet.Applet;
 
public class ScrollStatus extends Applet implements Runnable {
 
    Thread thread;
    String message;
    StringBuffer buffer;
    int at;
    int width;
 
    public void init(){
        message = getParameter("message");
        if(message == null)
          message = " Isn't scrolling text in the status line annoying? ";
 
        String ws = getParameter("width");
        if(ws == null) width = 36;
        else{
            width = Integer.valueOf(ws).intValue();
        }
        if(width < 5 || width > 180)
          width = 36;
 
        buffer = new StringBuffer(width);
        buffer.setLength(width);
        at = 0;
 
        if(message.length() < width){
            char buf[] = new char[width];
            for(int i = 0; i < width; ++i)
              buf[i] = ' ';
            message.getChars(0, message.length(),
                             buf, (width - message.length()) / 2);
            message = new String(buf);
        }
    }
 
    public void start(){
        thread = new Thread(this);
        thread.start();
    }
 
    public void stop(){
        thread.stop();
    }
 
    public void scroll(){
 
        int l = message.length();
        int k = at;
        for(int i = 0; i < width; ++i, ++k){
            if(k >= l)
              k = 0;
            buffer.setCharAt(i, message.charAt(k));
 
        }
        getAppletContext().showStatus(buffer.toString());
        at++;
        if(at >= l)
          at = 0;
 
/*
   This seems to work just as well (or poorly :(. I thought that it might be
   creating a lot of strings for the GC to clean up though.
   the "buffer" and "at" variable are not needed for this code.
 
        String msg = message.substring(0, width-1);
        getAppletContext().showStatus(msg);
        msg = message.substring(1);
        message = msg + message.charAt(0);
*/
    }
 
    public void run(){
        while(true){
            scroll();
            try{
                Thread.sleep(25); // wait 25 ms
            }
            catch(InterruptedException e){
                break;
            }
        }
    }
}

How do I display the contents of a remote location defined by a URL within a container of an applet?

How do I interface with DDE?

(Submitted by Martin Higgins)

Try http://www.apc.net/neva/java/ for a DDE server implemented using native methods. Not ideal but I think its probably the only way.

How do I cause the browser to load a new applet, based on information obtained in the current applet?

How do I get the URL of documents showing in other Netscape frames?

How do I update an applet in a static Netscape frame when I load new content into another (dynamic) Netwscape frame?

"For example, I would like a scrolling banner in one frame to announce the content that is displayed in another frame."

How do I access username/password-protected URLs on an HTTP server? (i.e. how do I actually send the username and password to the server)

(Submitted by Eric Zarko)

Have the html page with the applet in the same directory. The browser will prompt the user for the username/password when they request the page and then remember it when it needs the graphics.

See also, "How do I retrieve an html page which is on an http server using authentication?" in the section, "CGI, Servers". -the editor

How do I create a frame without the warning window at the bottom?

(Submitted by Matt Durham)

(Editor's note: We do not recommend that programmers use this technique.)
Here is how the no warning thing works, at least as I do it:
First, set some flag to indicate that the thing isn't shown yet.
In init():

make a Frame but don't .show() it.
Make a window on that frame, and reshape it as you please.
.show() the window, and add "this" to it(dont use this.show() yet.
reshape "this" to something equal or greater in size than the window.
In run() or handleEvent(): make a call to repaint()
In paint():

check the flag you set.
if true, do a this.show() and set the flag as false.
There are a number of variations on the theme, it really doesn't matter what order you do some of the steps in. The point is, don't do this.show() until after the window is shown, and do it outside of init a call from handle event to repaint in the case of WINDOW_EXPOSE works.
If you try to reshape the window, the string will reappear unless you hide "this", reshape the window, then show "this" again.
If the applet stops running, the warning string will generally reappear.
- Matt Durham, Feb. 13, 1997
Here is the code:
import java.awt.*;

public class nowarn extends java.applet.Applet implements Runnable{

Frame framey;
Window winny;
Thread runny;
boolean startflag=true;

public void init(){
setBackground(Color.black);
framey=new Frame();
winny=new Window(framey);
winny.show();
this.resize(500,300);
winny.add(this);
this.move(0,0);
start();

}//end init

public void start(){
if(runny==null){
	runny=new Thread(this);
	runny.start();
}
run();
}//end start

public void stop(){

if(runny!=null){
	runny.stop();
	runny=null;
}
}//end stop

public void update(Graphics g){
paint(g);
}//end update

public void paint(Graphics g){

if(startflag){
      winny.reshape(20,20,300,300);
	this.show();
	startflag=false;
	}//endif: first time through only

}//end paint

public void run(){
while(true){
	repaint();
try{runny.sleep(100);}
catch(InterruptedException e){}
}
}//end run

}//end nowarn
HTML:
<html>
<head>
<title>
Look, no warning...
</title>
</head>
<body bgcolor="#FFFFFF">
<applet code="nowarn.class"></applet>
</body>