<p>How can I refer a custom function in xml?  Suppose that I have a function written in Java and want it to refer by the xml tag, how is this possible?</p>

<p>Current senario: I am using XACML2.0 which contains xml tags and I want to refer some function in Java that will talk to the backend data, I'm unable to refer a function in xacml.  Could you help me please?</p>

You should read up on Reflection in Java.
The following example would invoke the method
myObjectThatContainsMethod#methodNameAsString(Integer arg1, Integer arg2)
```
```
Integer[] params = {new Integer(123),new Integer(567)}; 
Class cl=Class.forName("stringParsedFromYourXML"); 
Class[] par=new Class[2]; 
par[0]=Integer.TYPE; 
par[1]=Integer.TYPE; 
Method mthd=cl.getMethod("methodNameAsString", parameterTypes); 
mthd.invoke(new myObjectThatContainsMethod(), params);
```
```
hope that helps..