At 15:39 14.01.2002 -0500, you wrote:
>That all worked fine, except that developers would make the mistake of
>putting the wrong class name inside the getInstance() method. This would
>usually happen when they would cut and paste code.
The idea of automatically discovering the caller class name has been
suggested before, I believe by Anders Kristensen along similar lines.
It would be nice to have a reliable method to retrieve the caller
class name. However, I am not aware of any such method.
>So, one of our developers came up with a clever solution to cut down on the
>mistakes. He created a logging utility that could automatically read the
>stack frames, discover which class logged the message, and invoke logging
>from the proper Category.
>
>Here is how he did it:
>
>public class LogUtil {
> /**
> * Extends <code>java.lang.SecurityManager</code> to provide the
><code>getClassName()</code>
> * method.
> */
> private static class ClassGetter extends SecurityManager {
> // Inner class necessary because getClassContext() is protected
>
> /**
> * Returns the name of the calling class.
> * @return the name of the calling class
> */
> public String getClassName() {
> // getClassContext() returns the current execution stack trace
> // as an array of classes -- the element at index 0 is the class
> // of the currently executing method, the element at index 1 is
> // the class of that method's caller, and so on. So, 0 is going
> // to be this class (ClassGetter), 1 will be LogUtil, and 2 will
> // be the magic number we are after.
> return getClassContext()[2].getName();
> }
> }
This is pretty smart. However, is it guaranteed to work? How long do
you think it will take you to debug a problem with
getClassContext()[2].getName() compared to a typo? The goal was to
avoid errors, remember? Can it be that you are trading one evil with
even a worse one?
If getClassContext()[2].getName() is guaranteed to work, then it is a
useful feature, otherwise it is evil. I would not take any chances...
> public static boolean DEBUG() {
> Category cat = Category.getInstance(classGetter.getClassName());
> return cat.isDebugEnabled();
> }
The DEBUG method calls Category.getInstance method which is
not particularly fast. As such, this DEBUG method will incur
a constant penalty. I suspect this is not what you want.
--
Ceki Gülcü - http://qos.ch
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