[Jython-users] Dynamic Java Class creation

[David M. <Dav...@te...>]

In one case, I am interested in using Jython to dynamically create a =
java class at runtime and I would like to explore this with you.

The general idea is that I want to dynamically (at runtime) create a =
java class that implements a certain interface, then instantiate that =
class and call its methods.  I'm inventing a contrived example here =
because it is hard to explain in a few words the exact application.  =
Suppose the java interface looks something like (its late so please =
avoid syntax:):

Interface MyCallInterface:
    {
    public int doCall();
    }


Now I want to generate a new class implementing the above interface, and =
with some specific logic in the doCall() method , based on some =
properties that occur at runtime (including some user input).  The =
doCall method has to act on other java objects based on some =
configuration data, so normally it would have to do reflection to look =
up the method names (configurable) and then call them.  But, that is =
slower than I want it to be and so is using dynamic proxies. =20

What I would like to do is something like this:

0) I would rather implement an interface than extend and existing java =
class if possible.

1) Build a string that contains the class definition (that inherits from =
MyCallInterface) and the method code for the doCall() method.

2) Pass that string into jython in some manner so that I get a class =
back that I can instantiate the object from.

3) Instantiate the newly defined object.

4) Call its doCall() method repeatedly during program operation until =
parameters change, at which point I would generate a new class =
definition and get a new object.

What I am hoping is that the performance using this approach (after the =
initial class compile) would be faster than reflection and dynamic =
calls, since they have more overhead than direct method calls.  Would my =
approach be faster or is there a lot of overhead the jython introduces?

Also, I can't see clearly how to do what I want.  Could anyone post a =
very short but complete hello world type example of how to do this from =
within a java program?

This has all kinds of neat implications for custom configurators and =
dynamic execution policies, but it should be really really fast.

Also, I have heard of some code from a GNU or Apache project that would =
generate bytecode for classes on the fly (or something like that) and =
that is the type of functionality I need (without myself having to =
understand the byte code).  If the jython approach won't work, can =
someone point me to the code I mentioned here?

THANKS!!

David