Re: Red X image displayed where the applet should be, applets won't run

From:

Nigel Wade <nmw@ion.le.ac.uk>

Newsgroups:

comp.lang.java.help

Date:

Thu, 03 Apr 2008 09:03:32 +0100

Message-ID:

<ft230k$c96$1@south.jnrs.ja.net>

Morten Gulbrandsen wrote:

Error as described here,

http://www.java.com/en/download/help/redximage.xml

most or nearly all applets from other pages display well in browser

this applet works with the appletviewer.

I got no help on the IRC channel irc.freenode.net #java as they have
the policy no applets.

I type this in a file

import javax.swing.*;

public class PreviewApplet2 extends JApplet
{

    static final long serialVersionUID = -3850477712741615045L;

    public void init()
    {
        JLabel niceLabel = new JLabel("Java is fun!");
        ImageIcon dukeIcon = new ImageIcon("duke_waving.gif");
        niceLabel.setIcon(dukeIcon);
        getContentPane().add(niceLabel);
    }
}

and compiles to a class

javac -Xlint PreviewApplet2.java

I have the examples from here

http://www-cse.ucsd.edu/users/savitch/ # my book is not listed,

Java:An Introduction to Computer Science and Programming, 2nd Edition

some other examples runs fine, from the command line, on windows
in the appletviewer and in the browser.

But this one gets
Red X image displayed where the applet should be, applets won't run

I use appletviewer PreviewApplet2.html

and that works fine.

permissions for the image is

-rwxrwxrwx duke_waving.gif

a change in permissions to

-rw-r--r-- did not help.

on the Tools Java console I can se

Java Plug-in 1.6.0_05
Using JRE version 1.6.0_05 Java HotSpot(TM) Client VM
User home directory = /export/home/morten
----------------------------------------------------
c: clear console window
f: finalize objects on finalization queue
g: garbage collect
h: display this help message
l: dump classloader list
m: print memory usage
o: trigger logging
p: reload proxy configuration
q: hide console
r: reload policy configuration
s: dump system and deployment properties
t: dump thread list
v: dump thread stack
x: clear classloader cache
0-5: set trace level to <n>
----------------------------------------------------
java.security.AccessControlException: access denied
(java.io.FilePermission duke_waving.gif read)
      at

java.security.AccessControlContext.checkPermission(AccessControlContext.java:323)

[snip long stack trace]

in the error console I can see the above msg.

I did google for
java.io.FilePermission duke_waving.gif

and found this explanation

How are you running the applet from the command line? In a browser? In
the appletviewer? Or as an application?

Security settings are different for all three. When applets run in a web
browser, access to the file system is, by default, not permitted. That
is normal.

End of explanation

I look it up from sun

http://java.sun.com/docs/books/tutorial/uiswing/components/icon.html#applet

Loading Images Into Applets

Applets generally load image data from the computer that served up
the applet.

For me it looks like a contradiction.

No, it's not a contradiction. Applets require a web server, and they load images
from the same web server as they were themselves loaded from (or from within a
jar obtained from the same server). If you attempt to load an applet from the
local filesystem, as you have done here, then the JVM classloader can load the
class you specify, but your class file cannot access the local filesystem
unless you sign the applet. This is for everyone's protection. Otherwise an
applet which you accessed via some random URL would be able to access your
filesystem, which I'm sure you don't want to be allowed.

If I include this line of code in the java file

ImageIcon dukeIcon = new ImageIcon("duke_waving.gif");
niceLabel.setIcon(dukeIcon);

I do expect java to do so

but the applet plugin won't do so, and for a very good reason.

and not additionally
append an <IMG SRC="filewithpicture.gif"> to the HTML code.

Huh?

--
Nigel Wade