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From "Doug Bateman (JIRA)" <>
Subject [jira] Commented: (LOGGING-137) LogFactory.getLog()
Date Wed, 18 Aug 2010 20:03:20 GMT


Doug Bateman commented on LOGGING-137:

It's not quite that simple, because the output of Throwable.printStackTrace(stream) isn't
standard.  For one thing, it varies based on the availability of line numbers.  So it is very
important that the length of the header be calculated dynamically, at least once.

Doing that calculation in getStackHeaderCharCount() doesn't work, because that method signature
doesn't match getCallerJava11(int).  So what it means is that I've got to call "public static
int getCallerJava11(depth)" itself to calculate the stack size up front.... and that means
I'm using that public function even before the final field STACK_HEADER_CHAR_COUNT is even
initialized.  It's messy.

However, fortunately I think it's still workable.  I can rely on the fact that static-initializers
are synchronized by the class loader, so I need not worry about race conditions caused by
having a public static method reading a static field prior to initialization.  And I can rely
on the non-initialized field having the default value zero prior to it's initialization. 
Otherwise it would be a real nightmare.

Anyway, I've got to finish installing these updates.  For the Java 1.4 version, I take it
you prefer Example where I simply assert STACK_HEADER_FRAME_COUNT=2,
(e.g. drop 2 frames and then read at depth) rather than doing any dynamic calculations.  Is
that correct?

> LogFactory.getLog()
> -------------------
>                 Key: LOGGING-137
>                 URL:
>             Project: Commons Logging
>          Issue Type: New Feature
>    Affects Versions: 1.1.2
>            Reporter: Doug Bateman
>         Attachments:,,,,
>   Original Estimate: 0.5h
>  Remaining Estimate: 0.5h
> Presently, in Apache Commons, the most common way to get a logger is to do something
> public class MyClass {
>     private static Log log = LogFactory.getLog(MyClass.class);
> }
> Notice how MyClass.class (or alternatively a string name) is passed as a parameter. 
The annoying aspect of this is that sometimes the class name doesn't get updated when doing
copy/paste operations.  A desirable alternative might be:
> public class MyClass {
>     private static Log log = LogFactory.getLog(); //class name inferred from call stack
> }
> With such an approach there are two possible concerns I can foresee:
>     * Call stack inspection isn't terribly fast.  However since Loggers are generally
initialized only once, when the class is first loaded, performance isn't likely to be a major
>     * Commons-logging is Java 1.1 compatible.  Thus care must be taken to ensure compatibility
isn't broken.
>     * Commons-logging doesn't depend on commons-lang, and thus the utilities in commons-lang
cannot be used.
> In Java 1.4, the call stack is easily obtained using Thread.getCallStack().  Prior to
Java 1.4, the only way to obtain the call stack is to inspect the stack trace of an exception.

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