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 17:04:13 +0100

Message-ID:

<ft2v5t$l41$1@south.jnrs.ja.net>

Morten wrote:

Nigel Wade wrote:

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

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.

Interesting </Morten>

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

Huh?

I will discuss the HTML <IMG SRC=""> tags later. </Morten>

Hi Nigel,

What! Applets require a web server?
Interesting.

http://tinyurl.com/35dt2b

http://tinyurl.com/3dr2e4

http://tinyurl.com/3a2268

http://tinyurl.com/2vf3cw

http://tinyurl.com/2t856d

this shows that some works and others woun't work.

esp this one http://tinyurl.com/35dt2b

it works like charm from the
Apache/2.0.61 (Unix) Server at xxxx Port 80

with images and permissions and no jar file

and this one http://tinyurl.com/2t856d
always fails with nasty stack trace.
And the Red X image displayed where the applet should be,
except when run from the appletviewer.

the example I'm using which is supposed to work both has as Java code

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

and in the html file containing the <applet> ... </applet> tag also
has an html tag like <IMG SRC="filewithpicture.gif">

In the docs IIRC I at least remember to have read something like
<applet> is incorrect it should have been <object> </object>

but since there are so many different browsers the safe and old
fashioned way is the traditional way and still IIRC if I remember
correctly the recommended tag is in 2008 the <applet>.

My interpretation of this is in order to be browser compatible
also as an additional safety tag also to include an <IMG> tag.

This can be due to the population of nonstandards proprietary web
browsers. I'm not discussing safari, opera or Linux web browsers.

but this is about a java applet and I feel it would be nearly correct
to create an html file containing only the <applet> </applet>
tag like this

<applet code=PreviewApplet2.class width="400" height="200">
</applet>

Applets require a web server is an incorrect statement.

file:///usr/jdk/instances/jdk1.6.0/demo/applets/TicTacToe/example1.html

works like charm
in my browser
in my applet viewer
and from my homepage
and it has pictures.

Ok, it looks like I was wrong.

I thought that an applet loaded from the filesystem had no access to the local
filesystem other than the original class/jar file it was loaded from. It
appears that the applet *can* access the local filesystem via the classloader -
it still has no direct access.

If you look at the source code in that applet you will see that it is loading
the images via the classloader:

notImage = getImage(getCodeBase(), "images/not.gif");
crossImage = getImage(getCodeBase(), "images/cross.gif");

In the applet of yours which fails you are attempting to access the file via the
filesystem directly (rather than via the classloader):

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

this is not allowed and results in
java.security.AccessControlException: access denied

--
Nigel Wade