Logging Example

[chris_grind]

I'm having trouble using Javassist for something I thought would be straightforward. Am I missing something obvious or is this a current limitation?

I'm trying to instrumentate some methods to determine how long they take to execute. So at the beginning of the method I need a line such as:
long start = System.currentTimeMillis();

then at the end of the method I want to print out how long the method took, such as:
System.out.println(System.currentTimeMillis() - start);

It doesn't seem like I can do this using Javassist unless I want to manipulate the bytecodes directly.

TIA - Chris

[chiba]

You're right.

Since the before advice and the after advice belong
to separate scopes, "start" cannot be shared among
them. Fixing this problem is in my Todo list but, sorry,
I haven't done it. :<

A quick fix is to make "start" be a static field.

[ravipal]

Hi,
There is a way to achieve the same in Javassist though:

You can use ExpEditor class to modify the method body and hence you could use the same Object /variable without declaring static.

e.g :

method.instrument(
//
new ExprEditor() {
public void edit(MethodCall m) throws CannotCompileException{

m.replace("{"+
"long start = System.currentMillis...();"+
"$_ = $proceed($$);"+

"System.out.println(System.current....-start);"+

"}");


}
}
);

[ravipal]

sorry for being abstract.. but please ignore the syntax part.

Thanks
Ravi