Re: Exception Handling

Lew <>
Sat, 10 Mar 2012 18:39:48 -0800
Novice wrote:

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.

Here's the code for getResources() with all comments and error handling
(aside from the empty catch block) stripped out:

static public ResourceBundle getResources(String baseName, Locale locale
   ResourceBundle locList = null;

Don't use throwaway initializations, usually.

   try {
     locList = ResourceBundle.getBundle(baseName, locale);
   catch (MissingResourceException mrExcp) {

Log and return 'null' if that's the recovery strategy for this exception.


   return (locList);

The program which is executing is Foo. It has a method called
getLocalizedText() which is the one executing
LocalizationUtils.getResources(). The value of the baseName is a constant
coded in an interface of constants called FooConstants which is
implemented by Foo. Here's the code for getLocalizedText() without any
error handling and just one relevant comment:

Using an interface to define constants is the "Constant Interface
Antipattern". (Google it.) Use a class to define constants, not an interface.

An interface is there to define a type. Using it merely to define constants
violates the spirit of interfaces, which is to avoid implementation.

private void getLocalizedText() {

   Locale locale = Locale.getDefault();

   this.myText = LocalizationUtils.getResources(TEXT_BASE, locale);
   this.myMsg = LocalizationUtils.getResources(MSG_BASE, locale);

   /* Work with the localized resources. */

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


   logger.error(message, exception);

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,
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 disagree.

I'd keep that class/method info in the log message. Line information is less
valuable unless your methods are far, far too long.

Now, finally, here are some questions:

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. Okay,

I disagree. You should end the program gracefully and get someone to fix the
programming error right away.

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

In the log file.

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

Always check all parameters for validity, either by an explicit check for a
public or protected method, or by controlling what's passed to package-private
or private methods.

A normal practice is to have an application-specific checked exception to
throw, or to throw the standard unchecked exception. For example:

  if (argument == null)
    final String msg = "null argument";
    IllegalArgumentException except = new IllegalArgumentException(msg);
    logger.error(msg, except);
    throw except;

or similarly for application checked exception 'FooException'.

   throw new FooException(new IllegalArgumentException(msg));

Somewhere up the stack you should catch the exception and convert it to valid
program state"

  catch(RuntimeException except)

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.

There is if you create one. That's why Java has the 'new' operator.

If I let getResources() throw NullPointerException if either parameter is

Better, use 'IllegalArgumentException'.

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.

Write the log at the point where you detect the error, not only further up the

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.

  IllegalArgumentException exception = new IllegalArgumentException(msg);
  logger.error("Unable to proceed", exception);

One other questions. When, if ever, should I execute System.exit() with a
non-zero integer? In my example, I know that program Foo can't proceed

Never. Program exit should be under user control.

without the resources it is trying to get in getResources() so if I
simply throw exceptions and write to the log and then let the program
keep going, I'm simply going to get another NullPointerException on the
first statement that tries to use the resources. I'm thinking that I
should do a System.exit(1) after I've logged a null parameter or in the
event of a MissingResourceException in getResources(). But I have yet to
see System.exit() used in ANY example of error handling in any resource
I've looked at so far.


Honi soit qui mal y pense.

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