Re: Aspect questions?

Novice <>
Sun, 26 Feb 2012 17:22:32 +0000 (UTC)
Lew <> wrote in news:jibso4$bv2$

Novice wrote:

Lew wrote:

Novice wrote:

Lew wrote:

Novice wrote:

Lew wrote:

Logging is a great use case for aspects. However, there are
alternatives to lessening logging's overhead, too. You have to
weigh costs and benefits.

What are other good ways to do logging?

log4j is my favorite.

Right now, the two main programs in my current project each
create their own logger and then pass it to the classes they call
in their parameters.

I don't think that's a good pattern. Which logging library are you

I'm using Java Logging. Does that answer your question or are you
asking something else?

I have each class create its own logger (log4j style shown:

    package eegee;
    import org.apache.log4j.Logger;
    import static org.apache.log4j.Logger.getLogger;
    public class Foo
      final Logger logger = getLogger(getClass());

      public void foo()
        // do the fooey stuff
          // do the trying stuff
        catch (FooException exc)
          String msg = "trying stuff failed. "+
          exc.getLocalizedMessage(); logger.error(msg, exc);
          throw new IllegalStateException(msg, exc);

This boilerplate is what aspects aim to remove from the code and I
espouse retaining.

My code is not terribly different than that.

Actually, what you do is different and some of that difference is

Why aren't you logging the exceptions?

Because this is the code that creates the logger. If it fails to
create the logger, where would you like me to log the exception?

Yeah, I figured that out after the fact. You were doing a weird thing
by creating a factory method to call the factory method to create the

And what you are doing here is radically different from what I
proposed, hardly at all similar in any respect. I don't understand
why you think it's similar.

Okay, maybe it's completely different then. I thought it was the same

No. The difference is that I put the logger code in each class, and
don't have a centralized factory factory. That's because the logging
framework already provides a factory and a way to configure it, so I
don't try to reinvent that entire mechanism.

Here's the actual code minus the Javadoc comment:

      public static Logger configureLogger(String className, String
logFilePath, String logFileName, Locale locale, Formatter
formatter, Level loggingLevel) {

My goodness, don't use TABs! Especially not in Usenet posts!


This use of a separate logger factory that takes over what the
logging framework already does is, well, curious.

      String METHOD_NAME = "configureLogger()"; //$NON-NLS-1$

You don't need this, and if you did it should be 'final' and named
according to the Java coding conventions.

I thought final was irrelevant in a method and only made a difference
for instance variables?

It's not irrelevant, depending on what you think is relevant. It
prevents reassignment of the reference, and as a comment lets
maintainers know the intent is to have an immutable reference.

But you are correct that is actually wasn't so necessary here.

Relevant was probably not the right word to use there but it was the
closest I could think of at the time. Some time ago, I saw a post where
someone had a local variable defined as final and someone remarked that
it wasn't necessary or appropriate or whatever to put final on a local
variable. That's all I meant to say. I'm happy to put final on my local
variables or leave it out, whichever is appropriate.

You're right about the case of the name. That should be methodName
for a method variable....

      /* Ensure that the mandatory parameters have all been
      specified. */ if (className == null) {
           throw new IllegalArgumentException("The name of the
           class must
be provided."); //$NON-NLS-1$

You didn't log this!

Where would you like me to log this?

'logger.severe()' right at the point, just before the throw.

And those "$NON-NLS-1$" comments are highly distracting.

Sorry, I should have stripped them and the tabs out of the code

Actually, you should indent with spaces not TABs routinely.

Fair enough. I've gone into Eclipse, nosed around until I found where the
tabs are created (in "Formatter") and created a new profile that uses
spaces instead of tabs.

And strip
out the superfluous comments in your own code, too - that is, if
they're actually superfluous.

When I write code, I typically write a comment first to express the
intent of what I want the next line or lines to do. Then I write the code
and leave the comment there due to the brainwashing I got in my early
days about always commenting everything. I try very hard to choose very
clear names for things like variables, methods, and classes and I'd like
to think the code is nearly self-explanatory most of the time without the
need for comments. I'm sometimes tempted to erase all or most of the
comments but then it occurs to me that what is obvious to me may not be
so obvious to a total beginner and maybe it's a good thing to leave the
comments there for their sake. In short, I agree that the comments in the
method I posted don't really need to be there for my sake but, as long as
I keep them accurate - and I usually do - they might conceivably help
someone else.


      if (logFilePath == null) {
           throw new IllegalArgumentException("The log file path
           must be
provided."); //$NON-NLS-1$

      if (logFileName == null) {
           throw new IllegalArgumentException("The log file name
           must be
provided."); //$NON-NLS-1$

      if (locale == null) {
           throw new IllegalArgumentException("The locale must be
provided."); //$NON-NLS-1$

      /* Create the logger. */
      Logger logger = Logger.getLogger(className);

      /* Create path identified by logFilePath if it does not
      exist. */ File path = new File(logFilePath);


I can't go on. It's too painful.

Why? Telling me it's awful without saying why doesn't teach me

I didn't stop there. I did say why.

I hadn't got that far yet ;-)

I put that in a utility class in my Common project. Then any
program that wants a logger just executes this one method passing
the appropriate parameters.

You don't need that. You just call 'Logger.getLogger()'. The utility
class is a whole lot of weird complication that you don't need.

But, splutter, but, ... that's what the existing
'Logger.getLogger()' method does!

You're doing everything by hand that the framework does for you!

So I just execute Logger.getLogger() and a logger will be magically
created that is exactly where I want it to be with exactly the file
name I want to ensure that it is in the right format, XML in my case
and with exactly the right logging level and handlers? I thought I
had to do SOME of the work to ensure I got what I wanted.

Yes, that is correct.

I gave your suggestion a try in my sandbox, where I'm playing with
Aspects. I wrote this little class:

package test;

import java.util.logging.Level;
import java.util.logging.Logger;

public class TestLogging {

public static void main(String[] args) {

TestLogging test = new TestLogging();

public TestLogging() {
Logger logger = Logger.getLogger("test");
logger.logp(Level.INFO, "myClass", "myMethod", "Monday");
logger.logp(Level.INFO, "myClass", "myMethod", "Tuesday");
logger.logp(Level.INFO, "myClass", "myMethod", "Wednesday");
logger.logp(Level.INFO, "myClass", "myMethod", "Thursday");
logger.logp(Level.INFO, "myClass", "myMethod", "Friday");
logger.logp(Level.INFO, "myClass", "myMethod", "Saturday");
logger.logp(Level.INFO, "myClass", "myMethod", "Sunday");

The code ran fine and the logging statements all appear nicely in red on
my console. So far, so good.

But I'd like them to appear in a log file somewhere, too. My has the following lines:

handlers= java.util.logging.FileHandler, java.util.logging.ConsoleHandler
java.util.logging.FileHandler.pattern = %h/java%u.log
java.util.logging.FileHandler.limit = 50000
java.util.logging.FileHandler.count = 1
java.util.logging.FileHandler.formatter = java.util.logging.XMLFormatter

By my reckoning, that should ensure that I'm also getting a log file and,
since I'm running on Windows XP, I should be able to find it at C:
\Documents and Settings\[Windows ID]\javaX.log. Well, I've got a
java0.log through java4.log in that directory but none of them contain my
logging statements.

The only other place I can find to look, suggested by this site -
guide/tracing_logging.html - translates to C:\Documents and Settings
\[Windows ID]\Application Data\Sun\Java\Deployment\log. There's exactly
one file in that directory and it is a Java log with the ungainly name of
plugin5581819941091650582.log but it contains only this:

<?xml version="1.0" encoding="windows-1252" standalone="no"?>
<!DOCTYPE log SYSTEM "logger.dtd">

I'm not sure where else to look so I'm going back to the docs to see what
other clues I can find. I suspect that the indirection involved in trying
to find the log files was another factor in which I decided to create the
loggers the way I did....

The logged files simply aren't much use if you can't find them.

I realize that I could have each class create its own logger and
log but



would seem to guarantee a proliferation of logs that would be a
pain to find. It seems reasonable to me that if I have a bunch of

No, no, no, no.

You don't create multiple log files, one per class. Where did you
get that notion?

Huh? You seem to be contradicting yourself. Are you saying I should
create one logging file per class or not? And why have a separate

No. I never said nor implied that you should have one logging file per
class. That one's on you, brother.

Okay. Your phrasing was a bit confusing. I read it as "You don't create
multiple files, (you create) one per class." Apparently that's not what
you mean after all. Sorry.

file for each class? Isn't it more logical to have all the messages
that come from one program, say Foo, appear in the same log? Isn't
the poor

Yes, but why are you arguing a point not in dispute?

Because your phrasing seemed to imply that I DID want one log per class.

Sysop going to be excessively busy if he has to check a separate log
for each and every one of the - hundreds? thousands? - of classes in
the system? Wouldn't it be more logical to group logs on the basis of
which application is invoking the class? Therefore, if method
getCurrentWeekdayName had problems while executing program Foo, the
Foo log would contain the information? Wouldn't the person running
Foo be the one that's notifying the SysOp that something screwy just
happened while running Foo? Then the name of the application would be
a huge head start in finding the problem: just look in the Foo log
and all will be revealed. Or at least enough to get started.

How you do go on.

No one is suggesting anything like that scenario. so cool your jets,


Sorry. I was confused by what you seemed to imply.

You set up the logging in the configuration file. Done. Simple.

What configuration file? I'm not sure what you mean. First, I'm not
sure what you mean by a configuration file. Second, are you saying
that all applications will normally have a configuration file? I
don't remember coming across those in the Java Tutorial, for example,
or even seeing them mentioned in this newsgroup.

A configuration file is a file that contains configuration

I'd guessed that much ;-) I'm trying to figure out what they contain,
where I put them, etc. Reading ahead, you're about to explain that....

As far as what you don't remember, if you follow the link from the API
docs for java.util.logging:

You come across a recommendation to read the introduction to Java
logging, which I sure hope you followed:
"Related Documentation
For an overview of control flow, please refer to the Java Logging
Overview." which links you to
.html> wherein you would have read, had you read it,
.html#a1.15> "The APIs are structured so that an initial set of
configuration information is read as properties from a configuration

As for the tutorials, you have
which among other links will find you
that covers a little about the "" file.

Actually, I have been in all of those documents in the last several hours
as I've been trying to puzzle out the right way to do logging. I'd seen
all of them before at some point, but it was a fair while ago. Back then,
I played with logging and came up with the logging code I posted (more
or less). I truly don't remember how I got to that code though. At a
guess, I didn't want the logs to go where the logging properties file
wanted to put it and wanted it in a directory within each project so that
it was more convenient, rather than putting all logs in the same

As for the term "configuration file" I didn't realize you meant
"". That was my confusion there; I don't recall hearing
that called a configuration file before and thought you were talking
about something completely new and outside my experience.

If this is some routine thing that professional developers do, great.
I obviously need to know about it. Can you point me to a tutorial or
whatever that will explain what they are and how to create them?

GIYF, dude.


You are re-inventing the logging wheel. You said,

Goodness no! I am using the Java Logging classes to do my logging.
Sorry if that wasn't clear.

but you aren't using it correctly. What you are doing is defeating
the built-in features and reinventing everything. Don't do that.

That was not my intention. I'm off to look at the logging classes
again and see how I can avoid reinventing the wheel. I'm really not
seeing why you say that yet. I'm using the standard Java Logging
classes. I've


not deliberately, I assure you.

tweaked the properties file that governs logging a little bit to get

Huh. That's the configuration file, dude.

Now the penny drops....

effect that I wanted and I created my own variant on the XMLFormatter
that is only very slightly different. Aside from that, I'm using the
vanilla logging classes. I'm not sure how that constitutes
reinventing the framework. But, as I said, I'm going to review the
logging classes now and see if I'm overcomplicating the creation of
the logger as you say. Perhaps I am....

The properties file specifies the log file, the log level (by type if
you so choose), the output format, whether you report the class and
method being logged - all the things you did manually in your utility

And when I said you should know both ju.logging and log4j, somehow
you inferred that to mean that you should use both in the same
program. Such leaps you make! Settle back and stick with inferences
that actually follow from what I say.

Well, here's the exact quote:

"Use log4j or java.util.logging (OR BOTH)". [emphasis added]

Not in the same code! Yeesh.


As I've said, I'm a one man Java shop in a town that doesn't seem to
do much Java. I don't work in a professional Java shop so I have no
professional Java code to look at or peers to learn from. So I'm
floundering. That's why this newsgroup is important to me. I _AM_
trying to get better at this....

Of course, hence the detailed feedback.

Which I appreciate, even if I seem a bit grumpy or frustrated at times.

But I'm still confused about the scope of my logs. According to the
logging overview, I want the argument to Logger.getLogger() to be "A name
for the logger. This should be a dot-separated name and should normally
be based on the package name or class name of the subsystem, such as or javax.swing."

I expect that they are assuming that each project has a unique package
name. Therefore, if my company is, then the Foo project will
presumably have a package named and the Bar project will
have a package named Then, the logging for the Foo
project will be based on Logger.getLogger(""), right? Then
every class within the Foo project will have the line:

Logger logger = Logger.getLogger("");

Have I got this so far?

If so, the next logical step would be to treat all the stuff in the
Common project similarly. If I put all of those classes in package
com.novice.common, then each class would have this:

Logger logger = Logger.getLogger("com.novice.common");

Or would it be better to get a reference to the logger within Foo and
pass that to the classes in the Common project so that they write to the
logger used by the instantiating class from Foo?

Now, as it turns out, I've actually got a bunch of packages in project
Common. I'm separating different kinds of common classes via packages.
I'm not sure now if that is a good idea or a bad one. I've got separate
packages with the Common project for utilities, for classes dealing with
preference handling, for classes that are just simple lookups (including
Enums), classes that create generic panels for GUIs, etc. So maybe I need
to ask first if it is a bad idea to separate my common code into
categories or if it is better to lump it all together into a single

If keeping the separate packages is a good idea, then I need a bit of
guidance on whether there should be a separate logger for each package or
whether I'm better to write all messages from all Common classes to the
same logger, e.g. com.novice.common despite their different packages.

Now, if Project Foo only uses code from one other project, Common, I only
have two logs to worry about, the one that has all the Foo stuff and the
one that has all the Common stuff. That's not too bad. Then again, maybe
it would be better to use Logger.getLogger("com.novice") and write every
message from every class I write to the very same log, regardless of
project. What is the best practice here?

I feel like I'm starting to see what you have in mind but I hope you stay
with me for just a bit longer until we've hashed the last bits out. I
don't want to go off in the wrong direction again so I need your
confirmation that I'm starting to get it now.


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