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From Tim Shaw <>
Subject Re: ClassCastException
Date Mon, 16 Jun 2003 20:25:20 GMT
 From memory,

Your ClassLoader has a constructor MyClassLoader() : 'inside' the 
constructor you call 'super( this.getClass().getClassLoader() )' - NB 
you can't actually do this as it involves doing stuff before the call to 
the super constructor, but the semantics are the same.

Now you override the loadClass( name ) method and use the name to derive 
the bytestream you need (the Class definition). This will only be called 
if the current Class loading delegation model can't find the class.
[That's the point at which I would load a blob ...]

After that, 'ClassNotFoundException's are your problem ;-)


Tim Shaw wrote:
> I've done a lot of dynamic class loading ... and have never needed to 
> use a custom class loader ('cept one time when I stored them in a DB ... 
>  don't go there!). I would re-evaluate why you need a class loader 
> rather than Class.forName( "someClassName" ).newInstance().
> My gut feeling is, if you don't know all about class loaders, you don't 
> need to use one (explicitly).
> My 2p
> tim
> Anna wrote:
>> i need to do some kind of dynamic plugin managment ... i retrieve 
>> files from directory .. and extract names ... after that i use these 
>> names to load classes dynamicaly ...
>> i catched article what did you post ... but i have some problems with 
>> this ... could you plz explain me how i can set my "classloader's 
>> parent to the current classloader"
>> Anna
>>   you need to set your classloader's parent to the current 
>> classloader. Have you reviewed Tomcat's classloader document so that 
>> you understand how tomcat works before trying to load your own classes?
>>   Is there a reason to do this as opposed to moving your classes into 
>> tomcat's WEB-INF directory? I wouldn't do this if you are just trying 
>> to avoid copying your files to tomcat's directory from your network 
>> drive.
>>   Charlie
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