Preprocessor logging statements in java

Question

for example I want to replace before compilation:

#debug("${enclosing_method} this is debug message for " + userName)

with:

if (log.isDebugEnabled())
{
  log.debug("<real method name> this is debug message for " + userName);
}

Answer 1

I would recommend AspectJ to accomplish your goal. It is not a preprocessor, but an aspect-oriented metaprogramming language for Java. You get all sorts of advantages by using AspectJ, like type safety and IDE support. It is quite a powerful language.

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To do what I think you want, I would recommend specifying a pointcut to match everything you would like to put your logging into. For example, this matches all the methods in MyType (you'll want something specific to your own code):

pointcut loggedMethod() execution(* *(..)) && this(MyType);

Then, you'll want to give advice to inject your logging statements:

before() : loggedMethod() {
    Log log = iDontKnowWhereLogComesFrom();
    if (log.isDefaultEnabled()) {
        String methodName = thisJoinPoint.getKind();
        log.debug(methodName + " is the debug message for " + iDontKnowWhereUsernameComesFrom);
    }
}

Which looks way wordier, except that you automatically support adding logging to any method that matches the pointcut without any changes, which means your actual methods can just look like:

public void foo() {
    // do whatever processing you want here without having to worry about the
    // cross-cutting concern of logging, since it is not at all associated with
    // your business logic
}

In my personal experience, this is a way more sustainable pattern than trying to implement and maintain your own custom preprocessor for this.

Answer 2

Consider using log4j if your example reflects your primary aim.

Quote needed: Preprocessor usage is bad OO practice could be of interest as well.

Answer 3

Don't. Use slf4j instead which allows you to avoid the check with {}.