is it possible to change this java code at runtime to insert some small code

Question

I have a quite large codebase. In many places I have a piece of code like this:

for (MyObjectType myobj : myList) {
   //...do something with myobj
}

MyObjectType is the basic object in my application, and I iterate over many of them very often. I have some log4j set up so that I log info about the MyObjectType instance I am dealing with:

for (MyObjectType myobj : myList) {
   MDC.put("myobj", myobj.identify());
   ...
   logger.error("this message contains info about myobj")
}

This is really helpful. Unfortunately there are tons of for looks like this where I forgot to use the mdc.put(). So I was thinking...would be some way to instrument the code so that:

I detect there is a for looping over a collection of MyObjectType
I insert this as first instruction inside the loop: MDC.put("myobj", myobj.identify());

If there is a way (using aop, instrumentation, some java agent?), how difficult would it be (maybe it's not worth the effort).

I have never used any java bytecode library, just spring aop lightly.

It is so a pity that Coccinelle doesn't support Java (yet)... Otherwise it'd have been the ideal tool for that job! — fge
– fge, Commented Dec 16, 2011 at 18:41
Instead of using magical tricks, try not to duplicate your code, because this is what caused you the problem. — Zoltan Balazs
– Zoltan Balazs, Commented Dec 16, 2011 at 20:54

Ozzy · Accepted Answer · 2011-12-16 20:34:51Z

1

If the iteration method is quite complex and you use it so much, maybe you should move it to a new utility class specifically for handling those functions? That way, you need to write something once and all the calls to the new static method will reuse the same code.

answered Dec 16, 2011 at 20:34

Ozzy

8,3327 gold badges58 silver badges96 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Bohemian · Accepted Answer · 2011-12-16 20:31:57Z

0

You can change/add classes at runtime using javassist.
It's practically black magic.

I have also used janino with great success.

edited Dec 16, 2011 at 20:31

answered Dec 16, 2011 at 19:48

Bohemian♦

427k103 gold badges603 silver badges750 bronze badges

Comments

Chris Aldrich · Accepted Answer · 2011-12-16 18:46:10Z

0

I believe you would have to do this at class loading time. I don't know how to do it myself. But our company uses an application by a vendor that instruments our application code this way.

It does seem odd to instrument something that should have been noticed by a programmer (IMHO). I was wondering why not use refactoring through an IDE like eclipse, etc., where you could locate all instances of something and then add the code? Both will require testing, but it will probably be tougher to debug issues to solve problems if you get your instrumentation wrong.

Just my opinion.

answered Dec 16, 2011 at 18:46

Chris Aldrich

1,9281 gold badge23 silver badges37 bronze badges

Collectives™ on Stack Overflow

is it possible to change this java code at runtime to insert some small code

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related