Question

For debugging purposes I need to keep track of a Class attributes changes.

For example consider the following class:

class Test {
    int myInt;
    String myString;
    ...

    public void setMyInt(int a) ...
    public void setMyString(String s) ...

    public printDebugLog();
}

void main() {
    Test t = new Test();
    t.setMyInt(5);
    t.setMyString("Hello");
    t.printDebugLog();
}

I want to output to be something like:

myInt => 5
myString => Hello

The easy solution is to create logs instantly. i.e. adding a Log function as follow:

void Log(String s) {
    System.out.println(s);
}

and then code the set functions like below:

void setMyString(String s) {
    myString = s;
    Log("myString => " + s);
}

this requires all the set functions to be written variously and I wonder if there are any better solution for such matter. For example it might be easier (if possible) to create a SetValue function which accepts two variables and set the first attribute to the value of the second object. or something like this.

Any idea?

Answer 1

To do this you should wrap your class with orthogonal code that performs logging.

Since your class does not implement interface you cannot use dynamic proxy, so you have to use one of solutions that use byte code engineering.

The strongest solution I know is AspectJ. But probably you even do not need it. You can use Javassist or CGLIb – the byte code engineering libraries that allow creating proxies that wrap classes, so you can add code that performs logging.