[icedtea-web] RFC: fix null dtd for swing applications rendering html

[Omair Majid]

Hi Deepak,

Thanks for taking a look at this!

On 10/26/2010 04:33 PM, Deepak Bhole wrote:
> * Omair Majid<omajid at redhat.com>  [2010-10-26 15:46]:
>> There has been a regression in netx: applications that render html
>> (using Swing components) now fail with a null pointer exception.
>> This problem can be reproduced by running the program at [1].
>>
>
> What caused this regression? I thought all the app context stuff was
> still disabled, with just the support added on the side?
>

The regression itself was caused by having security dialogs in one 
AppContext and the actual application in another AppContext.

The AppContext stuff is enabled and working (in fact, some of the 
AppContext code was part of the original import of Netx into IcedTea and 
has been active ever since - most of my recent patches are about 
enabling it in the plugin case too and using AppContext correctly to 
gain its benefits). It is what allows multiple applets to have their own 
look and feels and allows security dialogs to always use the system look 
and feel without setting the look and feel of applets (or jnlp 
applications) too. I thought I had made it pretty explicit in my patches 
and changelogs :(

What is still disabled is allowing applets/applications to access their 
individual EventQueues. This is because of a security patch that has 
been recently been committed to OpenJDK7. This patch provides some 
additional API and says (and I am paraphrasing): "here is some API that 
allows the proprietary plugin to check if AWT events are generated by 
the system". I dont know how to make use of it, so I havent added code 
to allow applets to access their EventQueues. At least one application - 
a swing demo, no less [1] - fails without this.

>> The problem is caused by how HTMLEditorKit/HTMLDocument and
>> ParserDelgator interact in the presence of multiple AppContexts. The
>> instance of the ParserDelegate is shared between multiple
>> HTMLEditorKit in different AppContexts. However, ParserDelegate
>> maintains a per-AppContext dtd instance. The dtd is valid in the
>> AppContext that created the ParserDelegate but null in all other
>> AppContexts. Using this null dtd throws a NullPointerException. This
>> is really a bug in OpenJDK6 rather than Netx. Fortunately, this bug
>> has been fixed in OpenJDK7 - ParserDelegate maintains an instance of
>> the dtd per runtime instead of per AppContext.
>>
>> The attached patch works around this bug. It manually creates a
>> ParserDelegate for each AppContext to avoid this problem.
>>
>
> Assuming you have tested this, OK for head.
>

Thanks
Omair

[1] http://download.oracle.com/javase/tutorial/ui/overview/demo.html