Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.java.programmer > #12423

Re: Additional logging questions

Show all headers | View raw

Novice wrote:
> Arne Vajhøj wrote:
>> Novice wrote:
>>> Basically, I'm looking for advice on what should always be logged by
>>> every class. I understand now that every class is going to have its
>>> own logger but what should be logged?

You log what reveals to someone reading the log what they want to know.

>>> Or to put it another way, are there cases where a class won't log at
>>> all?

That depends on the logging level set at runtime, doesn't it?

If a class is unable to log anything, and that omission deprives someone of 
necessary information when they're relying on the log, it's a mistake.

If no one ever needs information from that class out of the log, it can get 
away with not logging.

>>> I'm thinking of things like Enums. If I have an enum that lists the

Enums are classes. The same considerations apply as for any other class.

>>> days of the week, there's not much to go wrong there and I'm not

Is there? I trust you - there's not.

>>> likely to throw exceptions or even have a try/catch block. So should
>>> it just be left so that it isn't logging at all? Or should there be
>>> some standard bare-minimum sort of logging, like an entering() and
>>> existing(), even if nothing else of interest goes on?

Good questions. Answer wisely, Grasshopper.

>>> What about holder classes? I'm not sure if I'm using the terminology

You are.

>>> correctly but I'm thinking of a class where you simply store related
>>> bits of data, like a Name class whose constructor insists on a first
>>> name and a last name and then supplies getters and setters so that
>>> another class can ask for just the first name or just the last name?
>>> (Let's pretend that everyone has exactly one given name and one
>>> surname, no exceptions, just to keep this simple). This could be an
>>> awfully barebones class if it only had a two line constructor and one
>>> line getters and setters. Should it log anyway?

Logging is generally for state changes.

>>> My feeling is that Lew would say NOT to log unless there was a good
>>> reason to log and then cite several good reasons to log. I'm not sure

Don't take advice from your fantasy of me unless it's good advice. Don't take 
advice from the real me unless it's good advice, either.

>>> if something like an enum or a holder class (if I've used the term
>>> correctly) would EVER justify logging though.

Sure.

Depends on what's in it, doesn't it?

>>> I may have completely misread Lew and, if so, I'm sorry. Maybe this
>>> is another premature leap....

Since I never before said what to log or not log that you've seen, there's 
been nothing to misread, has there?

Nothing to read, nothing to misread. It's a simple equation.

>>> Some of the rest of you may differ dramatically on what should be
>>> logged and when it is okay not to bother. I hope some of you can
>>> share those thoughts with me.
>>>
>>> Basically, I'm just about ready to start getting loggers for each and
>>> every class in the project I'm working on now (with plans to do the
>>> same in every project as I create it or return to it). But I don't
>>> want to do too much logging either.....
>>
>> You should log the information you expect potentially could be
>> useful when troubleshooting a problem.

This requires that you think like a useful person, not a computer programmer.

When you're troubleshooting a log, you don't have code in front of you. You 
have what the log tells you. It had better God-damned tell you what you need, 
because you wouldn't be looking if someone weren't breathing down your neck. 
No fancy "***********************=============" strings. Logs are dense, 
multi-mega- or gigabyte beasts of tightly printed strings.

Ops personnel read logs. Ops personnel think programmers are children. I had 
an ops mentor who told me, "We love getting the programmers from [the 
development location] here for six months. They go back to coding _changed_!"

Other times they're cursing the programmers who wrote such lame logging 
statements.

>> And as a general rule, then if any doubt then log, because it
>> is usually better to have too much logging than too little
>> logging.
>>
>> I do not see any need for logging in an enum or in a pure
>> data class (holder class).

Some enums.

Like any other class, it depends on what it does. But generally you log state 
changes, i.e., behavioral methods (not usually attributes). You log anything 
that is weird. You log errors and warnings.

You pick appropriate logging levels.  Here's my log4j idiom:

  public void loadResource()
  {
    logger.debug("");

    final BufferedReader reader;
    try
    {
      reader = new BufferedReader(new InputStreamReader(getClass()
          .getResourceAsStream("/config/configuration.txt")));
    }
    catch(IOException exc)
    {
      String msg = "Cannot open configuration. "+ exc.getLocalizedMessage();
      logger.error(msg, exc);
      throw new IllegalStateException(msg, exc);
    }
    assert reader != null;

    try
    {
      // read the Reader, etc.
    }
    catch(IOException exc)
    {
      String msg = "Cannot read configuration. "+ exc.getLocalizedMessage();
      logger.error(msg, exc);
      throw new IllegalStateException(msg, exc);
    }
    finally
    {
      try
      {
        reader.close();
      }
      catch(IOException exc)
      {
        String msg = "Cannot close configuration. "
                     + exc.getLocalizedMessage();
        logger.warn(msg, exc);
      }
    }
  }

Note the multiple uses of 'logger' (an instance member) in that method.

>> But please add a toString method in your data class, so
>> when the class with real login in that uses the data class
>> can log it and you get something useful in the log about the
>> data.
>>
> Sorry, I'm not following you.
>
> Are you saying that the toString() method needs to be there to turn
> things like references into meaningful information? I know that a
> reference to something like a JFrame is not going to be very meaningful
> and would rather display the name given the JFrame via setName(). Or are
> you saying something quite different?

'toString()' should always give a useful way to identify the specific instance.

It should depend on (and usually only on) the same fields used to drive 
'hashCode()' and 'equals()' and if supported, 'compareTo()' (which should 
always be consistent with each other).

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Additional logging questions Novice <novice@example..com> - 2012-02-27 02:02 +0000
  Re: Additional logging questions Arne Vajhøj <arne@vajhoej.dk> - 2012-02-26 21:08 -0500
    Re: Additional logging questions Novice <novice@example..com> - 2012-02-27 04:12 +0000
      Re: Additional logging questions Lew <noone@lewscanon.com> - 2012-02-26 22:13 -0800
        Re: Additional logging questions Novice <novice@example..com> - 2012-02-27 19:14 +0000
          Re: Additional logging questions Lew <noone@lewscanon.com> - 2012-02-27 12:32 -0800
          Re: Additional logging questions Lew <noone@lewscanon.com> - 2012-02-27 13:06 -0800
            Re: Additional logging questions Novice <novice@example..com> - 2012-02-28 01:48 +0000
              Re: Additional logging questions Arne Vajhøj <arne@vajhoej.dk> - 2012-02-27 20:57 -0500
                Re: Additional logging questions Lew <noone@lewscanon.com> - 2012-02-27 23:51 -0800
          Re: Additional logging questions Arne Vajhøj <arne@vajhoej.dk> - 2012-02-27 20:50 -0500
            Re: Additional logging questions Lew <noone@lewscanon.com> - 2012-02-27 23:57 -0800
        Re: Additional logging questions Arne Vajhøj <arne@vajhoej.dk> - 2012-02-27 20:45 -0500
          Re: Additional logging questions Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-02-28 01:52 -0600
            Re: Additional logging questions Arne Vajhøj <arne@vajhoej.dk> - 2012-02-28 17:20 -0500
            Re: Additional logging questions Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-02-28 20:26 -0400
      Re: Additional logging questions Arne Vajhøj <arne@vajhoej.dk> - 2012-02-27 20:34 -0500
  Re: Additional logging questions Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-02-27 12:36 -0800
    Re: Additional logging questions Novice <novice@example..com> - 2012-02-28 01:43 +0000

csiph-web