Custom class loader

[spaceman]

Hi,

How can I create a custom class loader which loads classes only from a
specific jar?
e.g. in my web apps web-inf/lib I have a.jar and b.jar and I'd like to
have two separate class loaders for each of them. Is it possible?
As these jars are libraries and do not have a main() etc.. or any other
entry point, how can I set the class loader for every class in the
jars?

Any advice is highly appreciated.
Thanks

 

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

How can I create a custom class loader which loads classes only from a
specific jar?
e.g. in my web apps web-inf/lib I have a.jar and b.jar and I'd like to
have two separate class loaders for each of them. Is it possible?
As these jars are libraries and do not have a main() etc.. or any other
entry point, how can I set the class loader for every class in the
jars?

WEB-INF/lib ? No !

Because they will be loaded by a parent classloader.

If the two jar files are outside of normal classloader search
path it is simple.

URLClassLoader cl = new URLClassLoader(urlofjar);
X o = (X)Class.forName(clsnam, true, cl).newInstance();

Arne

 

[spaceman]

Thank You.

WEB-INF/lib ? No !

Let me be more specific. The problem I have is that both a.jar and
b.jar have some classes which are the same ( duplicated ). If I put
them toghether in WEB-INF/lib the classloader gets messed up due to the
duplicate classes.

Because they will be loaded by a parent classloader.

If the two jar files are outside of normal classloader search
path it is simple.

URLClassLoader cl = new URLClassLoader(urlofjar);
X o = (X)Class.forName(clsnam, true, cl).newInstance();

This seem to be a good possibility however as there is no entry point
and there are a lot of classes, I'm not sure how I can control the
creation of each class and use my own class loader.
Also how can I have the web server load the jars at some point if they
are not in web-inf/lib?

 

[=?ISO-8859-1?Q?Arne_Vajh=F8j?=]

Let me be more specific. The problem I have is that both a.jar and
b.jar have some classes which are the same ( duplicated ). If I put
them toghether in WEB-INF/lib the classloader gets messed up due to the
duplicate classes.

Yes.

You need two custom classloaders one for each jar and the jars
must not ne in path for parent classloaders.

This seem to be a good possibility however as there is no entry point
and there are a lot of classes, I'm not sure how I can control the
creation of each class and use my own class loader.
Also how can I have the web server load the jars at some point if they
are not in web-inf/lib?

The Class.forName code above explicit specify classloader.

The URL for the classloader can be any URL including file
URL's.

Note that the deployment of you app will become a bit tricky, but
that is how it has to be.

Arne