Re: Exception Handling

From:
=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 12 Mar 2012 14:37:18 -0400
Message-ID:
<4f5e4260$0$293$14726298@news.sunsite.dk>
On 3/10/2012 8:51 PM, Novice wrote:

I've been trying to get my head around exception handling for the last
few days concurrently with my efforts to start doing logging correctly.

I've re-read the Java Tutorials section on exception handling. I read
Bloch's remarks on Exception Handling in Effective Java (2nd edition)
several days ago. I'm working my way through Stelting's Robust Java.

It's time to ask some questions to make sure I'm on the right track.

I'm struggling with the best way to revise some of my existing code.
Let's consider a concrete example and then see if we can generalize to
come up with a proper error handling strategy.

I have a utility class called LocalizationUtils which basically houses
convenience methods dealing with i18n/l10n. One of its methods is
getResources(). It expects two parameters, a String representing the
"base name" (the leading part of the resource file name) and a locale.

In terms of trouble spots, I know from experience that getResources()
will throw a MissingResourceException, which is an unchecked exception,
if the base name is misspelled. A null value in either parameter is also
going to make the getResources() method fail: ResourceBundle.getBundle()
will throw a NullPointerException if either parameter is null.

My objective is to code getResources() and getLocalizedText() as
professionally as possible. If the methods fail, I want to write a clear
message to my log and the log record needs to include a stacktrace. (I'm
assuming that a console is not necessarily available to the operators
running this program and I need to know where the error took place. Based
on an article Arved suggested in another thread,
http://www.javacodegeeks.com/2011/01/10-tips-proper-application-
logging.html, I'm inclined to minimize "position" information - class
name, method name, line number - in the log and instead get all of that
from the stacktrace.)


I would not worry about the performance until you know that you
have a problem.

Since the only exceptions I anticipate, MissingResourceException and
NullPointerException, are unchecked exceptions, I gather than I shouldn't
really do anything about them aside from logging when they happen.


If you only log - then what?

                                                                   Okay,
fair enough; I certainly don't want to display the source code to my
user, make them enter the correct value for the baseName, make them
recompile the program and then run it again! But when/where should I log
the error? For instance, if I mess up my coding somehow and inadvertently
pass a null in the baseName, should getResources() be testing its input
parameters individually to see if they are null and write a message to
the log if they are null from within that method? I'm inclined to say yes
to that but I'm not sure what to do next. It seems pointless to carry on
with getResources() since ResourceBundle.getBundle(baseName, locale)
will fail on a NullPointerException with a null in either parameter. I
could throw a NullPointerException so that getLocalizedText() can deal
with it. But how do I get a stacktrace into the log if I follow that
strategy? It's easy enough to get the stacktrace once I've caught an
exception but I'm just talking about recognizing that an input parameter
is null; there's no exception at that point to put in my log.

If I let getResources() throw NullPointerException if either parameter is
null, then I can let getLocalizedText() catch those NullPointerExceptions
and get the stacktraces from the exception and write them to the log. In
that case, I may as well just check the input parameters for nulls, and
simply throw NullPointerException with a specific message within
getResources(); then getLocalizedText() can have a try/catch block. The
try/catch can detect the NullPointerException and write both the message
and the stacktrace to the log.

But I gather that you should handle the error as close to where it
happened as possible when you can. I'd tend to prefer to handle the null
parameter values in getResources() except that I'm not sure how to write
the stack trace to the log before any exception has happened.


Do you need the stacktrace in that case?

One other questions. When, if ever, should I execute System.exit() with a
non-zero integer?


When you want to terminate the program with an error status to the
shell.

Arne

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