openjdk team mailing list archive
-
openjdk team
-
Mailing list archive
-
Message #08826
[Bug 199732] Re: applet fails to load with nullpointerexception
Launchpad has imported 5 comments from the remote bug at
http://icedtea.classpath.org/bugzilla/show_bug.cgi?id=189.
If you reply to an imported comment from within Launchpad, your comment
will be sent to the remote bug automatically. Read more about
Launchpad's inter-bugtracker facilities at
https://help.launchpad.net/InterBugTracking.
------------------------------------------------------------------------
On 2008-09-02T00:07:03+00:00 Java-l wrote:
This is an upstream report based on Ubuntu Bug LP #199732
https://bugs.launchpad.net/ubuntu/+bug/199732
== Overview ==
Loading some Java applets via Firefox and the plugin with openjdk-6
results in:
Exception in thread "main" java.lang.NullPointerException
at sun.applet.PluginMain.start(PluginMain.java:211)
at sun.applet.PluginMain.main(PluginMain.java:73)
See, for example:
http://www.jeacle.ie/mortgage/ca/
http://wypte.acislive.com/pda/pda_maps.asp?SysId=30
I'll detail the analysis and the fix after this explanation.
== Background ==
There are an unknown number of Internet sites hosting Java applets that
fail when using the icedtea plug-in but work using the Sun Java plug-in.
The reason for the failure is usually a result of the historic mess that
was made of the HTML EMBED, APPLET, and OBJECT tags.
As a result of the various contrived work-arounds that web-site authors
used to try and ensure that all browsers managed to load a Java applet,
there are many combinations of these tags and the PARAM name/value
attribute tags that attempt to use browser quirks to ensure the user
does see the Java applet.
There has never been a standard for the EMBED tag particularly, it
having grown over time from its beginnings in Netscape Navigator. There
have likewise been various unofficial extensions to the OBJECT tag - the
only properly standardised tag - which should really replace the other
two tags in modern browsers and web-applications.
As a result users often suffer, caught between a rock and a hard place
when things go wrong - such as this NullPointerException - since they
have no influence over the web-site operators in most cases, and often
get told by developers that it is the web-site's problem, not the plug-
in, despite the widespread use of varying combinations of browser-
specific tag combinations. (See, for example, the responses in Bug
#151).
== The Issue ==
In the cases I've dealt with the failures are caused by the use of the
EMBED tag with no "code" attribute.
However, the HTML author has attempted to ensure all browsers/Java plug-
ins load the applet by including OBJECT and/or APPLET variations as well
as using PARAM name/value pairs.
The plug-in currently refuses to accept a tag-set passed by the browser
plug-in *before it has been completely parsed* if the initial tag isn't
of the form:
<EMBED CODE="" WIDTH="" HEIGHT=""> ... </EMBED>
It will also then ignore any PARAM name/value pairs as being "outside an
APPLET tag". This is unfortunate since in many cases the PARAM pairs
contain values that the plug-in can use to load the applet successfully.
== The Solution ==
The patch I've created refines the way PluginAppletViewer.parse() deals
with the EMBED tag. It adopts the same logic as is already present for
the OBJECT tag, deferring rejection of the attributes until the closing
tag, and thus allowing any PARAM name/value pairs after the opening tag
to be parsed into the attributes Hash.
When the closing EMBED tag is parsed, if there is still no "code" or
"object" attribute, the patch makes one last attempt to locate the
entry-point class. It first looks for the attribute "classid". If it is
found, the patch further checks that the value is prefixed "java:". If
so, a new "code" attribute is created and assigned the remaining
characters of the "classid" value. This will allow the applet to start.
E.g. <PARAM name="classid" value="java:org.some.main.class"/>
If any of these attempts fail it nullifies the attributes hash and fails
with the same message as previously.
This patch allows the plug-in to work with many more combinations of
OBJECT, APPLET, and EMBED tags and improves the user experience and
perception of openjdk and icedtea.
== Exception Analysis ==
This bug is caused when the Java plug-in hasn't had a window registered
using PluginMain.registerWindow(), which will set
PluginMain.currentWindow.
Without PluginMain.currentWindow set (it is initialised to null), when
the gcjwebplugin sends the applet the "width" message, the applet's
PluginMain.start() message-reading loop reads the width correctly, but
then tries to get the internal height property using:
int height = currentWindow.getHeight();
Because currentWindow is NULL it causes the Null Pointer Exception on
line 211.
The problem is caused in PluginAppletViewer.parse(...). There are
several overloaded versions of this function but they all pass through
to the work-horse overload that takes a complete set of arguments.
In PluginAppletViewer.parse() it scans the HTML APPLET/OBJECT/EMBED tag
and extracts the attribute values. When it finds an EMBED tag it passes
it to PluginAppletViewer.scanTag(). That method is responsible for
scanning the attributes inside the EMBED tag and assigning them to the
attributes Hash.
When scanTag() returns the EMBED detection-logic does some sanity checks
on the attributes to ensure it has what it needs to execute the applet
successfully. It checks for the CODE, WIDTH, and HEIGHT attributes not
being null. If any one of them is null it sets the attribute reference
to null too - effectively wiping them all out.
When the logic in PluginAppletViewer.parse() finds the closing tag
</EMBED> it checks if the attributes reference IS NOT null and if so
calls PluginAppletViewerFactory.createAppletViewer(). That in turn calls
PluginMain.registerWindow() which, as I said at the beginning, sets
PluginMain.currentWindow.
But, because an attribute of the EMBED tag was missing, the attribute
Hash reference was null and so PluginMain.registerWindow() wasn't called
and PluginMain.currentWindow remained with its initialised value, which
is null.
Hence the bug.
In the case of the sites here the missing attribute is "code", and you
can see the warning in the output:
Warning: <embed> tag requires code attribute.
That really should say "Error" since it is fatal.
Because the EMBED tag was not part of a W3C standard the definition of
legal parameters is hazy. It has been introduced for HTML 5 *but* will
not support the CODE attribute.
== Patch ==
Currently the patch is included in a provisional Ubuntu openjdk-6 source
package as
debian/patches/plugin-embed-use-param-translate-classid-to-code.patch
It would be preferable to have it included upstream since other
distributions have bugs reported for the same issue.
The patch could easily be moved to ./patches/ in the openjdk-6 source
package, as long as it is applied after
patches/icedtea-plugin.patch
Reply at: https://bugs.launchpad.net/ubuntu/+source/icedtea-
gcjwebplugin/+bug/199732/comments/14
------------------------------------------------------------------------
On 2008-09-02T00:09:14+00:00 Java-l wrote:
Created attachment 90
Defer EMBED attribute decision; accept wider range of OBJECT/EMBED/APPLET attribute permutations
Reply at: https://bugs.launchpad.net/ubuntu/+source/icedtea-
gcjwebplugin/+bug/199732/comments/15
------------------------------------------------------------------------
On 2008-09-02T08:32:34+00:00 Mark J. Wielaard wrote:
Deepak, you probably want to look into this one.
Reply at: https://bugs.launchpad.net/ubuntu/+source/icedtea-
gcjwebplugin/+bug/199732/comments/18
------------------------------------------------------------------------
On 2008-09-05T17:51:35+00:00 Dbhole wrote:
Just for the record, item has been fixed in the IcedTea plugin. I will
get to the GCJ plugin shortly.
http://www.jeacle.ie/mortgage/ca/ now works with the IcedTeaPlugin.
http://wypte.acislive.com/pda/pda_maps.asp?SysId=30 still fails, but the problem appears to be in the applet itself:
Exception in thread "Thread-11" java.lang.NullPointerException
at BusMap.run(BusMap.java:205)
at java.lang.Thread.run(Thread.java:636)
Reply at: https://bugs.launchpad.net/ubuntu/+source/icedtea-
gcjwebplugin/+bug/199732/comments/24
------------------------------------------------------------------------
On 2008-10-28T20:07:58+00:00 Dbhole wrote:
Both, http://www.jeacle.ie/mortgage/ca/ now works and
http://wypte.acislive.com/pda/pda_maps.asp?SysId=30 now work with the new plugin in release 1.3.1+.
Closing issue.
Reply at: https://bugs.launchpad.net/ubuntu/+source/icedtea-
gcjwebplugin/+bug/199732/comments/27
--
You received this bug notification because you are a member of OpenJDK,
which is subscribed to openjdk-6 in Ubuntu.
https://bugs.launchpad.net/bugs/199732
Title:
applet fails to load with nullpointerexception
Status in OpenJDK:
Fix Released
Status in “icedtea-gcjwebplugin” package in Ubuntu:
Won't Fix
Status in “openjdk-6” package in Ubuntu:
Fix Released
Status in “openjdk-6” package in Fedora:
Fix Released
Bug description:
Binary package hint: icedtea-java7-plugin
I am trying to access an applet from http://www.jigzone.com. The
applet fails to load with error:
Exception in thread "main" java.lang.NullPointerException
at sun.applet.PluginMain.start(PluginMain.java:211)
at sun.applet.PluginMain.main(PluginMain.java:73)
I am running Hardy Alpha 6 (firefox3, icedtea-java7). The applet works just fine on my Gutsy box (firefox2, sun6).
I have attached the complete console output
ProblemType: Bug
Architecture: i386
Date: Fri Mar 7 23:13:26 2008
DistroRelease: Ubuntu 8.04
Package: firefox 3.0~b3+nobinonly-0ubuntu4
PackageArchitecture: all
SourcePackage: firefox-3.0
Uname: Linux 2.6.24-11-generic i686
To manage notifications about this bug go to:
https://bugs.launchpad.net/openjdk/+bug/199732/+subscriptions
