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From Eli <elikat...@yahoo.com>
Subject Re: Registering Plugins, e.g. javax.imageio...
Date Wed, 11 Sep 2013 17:45:46 GMT
Don't know I'm in this email chain I need to ask someone that really knows computers 

Sent from my iPhone

On Sep 11, 2013, at 1:43 PM, Christopher Schultz <chris@christopherschultz.net> wrote:

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> Konstantin,
> 
> On 9/11/13 12:44 PM, Konstantin Kolinko wrote:
>> 2013/9/11 Christopher Schultz <chris@christopherschultz.net>:
>>> On 9/10/13 6:34 PM, George S. wrote:
>>>> 
>>>> On 9/10/13 3:14 PM, Christopher Schultz wrote:
>>>>> ----- Is there a way that I can specify something in the 
>>>>> server.xml code that would register them? The only thing I
>>>>> can see is to create a org.apache.catalina.LifecycleListener
>>>>> and put the code to register the plugins in there.
>>>>> 
>>>>> Is there some other way of doing it? How would you do it if
>>>>> you weren't running under Tomcat?
>>>> 
>>>> I only ever run Java with tomcat (or maybe ant), so I wouldn't 
>>>> know.
>>> 
>>> Okay. I had never heard of an "imageio plugin" before. Are you 
>>> basically registering file-type handlers?
>>> 
>>> I'm just guessing at all of this, since I've never done anything 
>>> besides use ImageIO for mundane operations like loading, saving,
>>> and re-sizing images.
>>> 
>>> Have you called ImageIO.scanForPlugins()?
>>> 
>>> The documentation gives light detains on how the plug-ins are
>>> found:
>>> 
>>> http://docs.oracle.com/javase/7/docs/api/javax/imageio/ImageIO.html#scanForPlugins%28%29
>> 
>> Those docs say that scanning is performed automatically on first
>> access.
> 
> Aah, yes. I didn't read it very closely :)
> 
>> As such, I would really recommend to write a Listener,  so that 
>> whatever classes are  found by scanning were loaded by the System 
>> classloader and had no references to the Webapp one.
> 
> The implications of doing this are that George will need to place the
> JAR file(s) containing his plug-ins in Tomcat's lib/ directory, so
> they can be picked-up by the top-level ClassLoader.
> 
> Using the existing JreMemoryLeakPreventionListener (with appropriate
> configuration) might take care of this... I don't exactly know when
> ImageIO will actually trigger this scan.
> 
>> Having unexpected references to the Webapp classloader would be
>> bad, as it leads to PermGen memory leaks.
> 
> +1
> 
>> The above is just a theoretical recommendation. I do not know how 
>> ImageIO manages those classes internally.
>> 
>> BTW, beware of known issue, mentioned in the FAQ, 
>> http://wiki.apache.org/tomcat/FAQ/KnownIssues#ImageIOIssues
> 
> +1
> 
> - -chris
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