how to record/monitor java field assignment operation

Question

how to record/monitor java field assignment operation ; for example , i want to add some function before or after the assignment operation;

original code :

class Test{
 public String name;

 public void operation{
             .... some code ...
         name="stackoverflow";
            .... some code ...
  }
}

After changing the code :

class Test{
 public String name;
 public void operation{
          .... some code ...
      [[ my instrument code ]] 
         name="stackoverflow";
      [[ my instrument code ]]
           .... some code ...
  }
}

NOTE: I want to instrument before or after every filed assignment line ; so it can not mannually point out which line should be instrument

is it possible using JAVA DEBUG INTERFACE ?? or is there any way to reach it INStrument or Dynamic Proxy

Answer 1

You can do that using javassist. Works for fields, but not arrays. I have done something like that in my fast serialization struct simulation:

method.instrument( new ExprEditor() {
                        @Override
                        public void edit(FieldAccess f) throws CannotCompileException {
                            try {
                                if ( ! f.isStatic() ) {
                                    CtClass type = null;
                                    type = f.getField().getType();
                                    FSTClazzInfo.FSTFieldInfo fieldInfo = clInfo.getFieldInfo(f.getFieldName(), null);
                                    if ( fieldInfo == null ) {
                                        return;
                                    }
                                    if ( f.isReader() ) {
                                        structGen.defineStructReadAccess(f, type, fieldInfo);
                                    } else if ( f.isWriter() ) {
                                        structGen.defineStructWriteAccess(f, type, fieldInfo);
                                    }
                                }
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                    });

from https://code.google.com/p/fast-serialization/source/browse/trunk/src/main/java/de/ruedigermoeller/heapoff/structs/unsafeimpl/FSTStructFactory.java

Answer 2

I think AOP is what you need. Read eg this http://www.javacodegeeks.com/2012/06/simple-introduction-to-aop.html