AOP to instrument classes on the fly ?

[belaban]

Okay, back to my old problem: I want to know whether an object has been modified within a given period of time. Here's what I would like to do:

Person p=new Person("Bela", 37);
cache.put("bela", p);
...
p.incrementAge();
...
if(p.isModified()) {
channel.replicate(p.toByteBuffer());
p.setModified(false);
}


The getModified() and setModified() methods are added to the class when the class is loaded. Possibly we also instrument the class with a method toStream() /fromStream, which provides efficient serialization, so my objects do not have to implement Serializable.


Can this be done ?

This would entail tracking state changes within the object.

Can you guys at class loading time find out whether a method is write or read-only ? If it is write add some code which sets an internal boolean "modified".

Am I far off ?

Bela

[marc.fleury]

> Person p=new Person("Bela", 37);
> cache.put("bela", p);
> ...
> p.incrementAge();
> ...
> if(p.isModified()) {
> channel.replicate(p.toByteBuffer());
> p.setModified(false);

essentially incrementAge() is a field access modification and the modification is instrumented meaning it is indirected. The cache.put("bela", p) triggers
((AOP)p).getStack(addInterceptor(new CacheInterceptor(this));

the Cache Interceptor is notified of setters changes.


>
>
> The getModified() and setModified() methods are added
> to the class when the class is loaded. Possibly we
> also instrument the class with a method toStream()
> /fromStream, which provides efficient serialization,
> so my objects do not have to implement Serializable.

essentially you get notified from the interceptor you dynamically add when someone inserts the entry in your cache.

> Can this be done ?

sure.

> This would entail tracking state changes within the
> object.

exactly and you get notified.

> Can you guys at class loading time find out whether a
> method is write or read-only ? If it is write add
> some code which sets an internal boolean "modified".

Again better, you instrument it for modifications. We just create the indirection.

marcf