Java – throwing runtime exception in Java application

exceptionsjavauser-experience

I am working as a contractor designing enterprise Java application for my client in the role of a technical lead. The application will be used by end users and there will be a support team who will support the application when we leave.

The other technical leads with whom I am working are under the impression that exception handling will make the code dirty. The system should throw checked exceptions only from the Service tier and the rest of the code should throw runtime exceptions from all other tiers so that there is no need to handle the unchecked exceptions.

What is a need to ever throw a unchecked exception in a business application?

From my experience in the past about runtime exceptions:

1) Unchecked exceptions make the code unpredictable because they do not show up even in the Javadoc.

2) Throwing Unchecked exceptions in a business application is non-sense because when you throw it and it goes straight on Users face, how do you explain it to the user? I have seen enough of web application which show 500 -Internal Error. Contact Administrator which means nothing for a end user or to the support team managing the application.

3) Throwing runtime exceptions forces the users of the class throwing the exception to walk through the source code to debug and see why the exception is thrown. This can only be avoided if the Javadoc of the runtime exception happens to be excellently documented which I find is never a case.

Best Answer

Checked exceptions are a failed expriment in language design. They force you to have extremely leaky abstractions and dirty code. They should be avoided as much as possible.

As for your points:

1) Checked exceptions make the code dirty, and no less unpredictable because they show up everywhere.

2) How is a checked exception being shown to the user any better? The only real difference between checked and unchecked exceptions is technical and affects only the source code.

3) Ever heard of stack traces? They tell you exactly where the exception was thrown, no matter whether it's checked or unchecked. Actually, checked exceptions tend to be worse for debugging because they're often wrapped which leads to longer and uglier stack traces, or even lost atogether because the wrapping was done wrong.

There are two kinds of exceptions: those that occur "normally" and are typically handled very close to where they occur, and those that are reallly exceptional and can be handled generically in a very high layer (just abort the current action and log it / show an error).

Checked exceptions were an attempt to put this distinction into the language syntax at the point the exceptions are defined. The problems with this are

The distinction is really up to the caller, not the code that throws the exception
It's completely orthogonal to the semantic meaning of an exception, but tying it to the class hierarchy forces you to mix the two
The whole point of exceptions is that you can decide at what level to catch them without risking to lose an error silently or having to pollute the code at intermediate levels or ; checked exceptions lose that second advantage.

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How to write a good exception message

I'll direct my answer more to what comes after an exception: what's it good for and how should software behave, what should your users do with the exception? A great technique I came across early in my career was to always report problems and errors in 3 parts: context, problem & solution. Using this dicipline changes error handling enormously and makes the software vastly better for the operators to use.

Here's a few examples.

Context: Saving connection pooling configuration changes to disk.
Problem: Write permission denied on file '/xxx/yyy'.
Solution: Grant write permission to the file.

In this case, the operator knows exactly what to do and to which file must be affected. They also know that the connection pooling changes didn't take and should be repeated.

Context: Sending email to 'abc@xyz.com' regarding 'Blah'.
Problem: SMTP connection refused by server 'mail.xyz.com'.
Solution: Contact the mail server administrator to report a service problem.  The email will be sent later. You may want to tell 'abc@xyz.com' about this problem.

I write server side systems and my operators are generally tech savvy first line support. I would write the messages differently for desktop software that have a different audience but include the same information.

Several wonderful things happen if one uses this technique. The software developer is often best placed to know how to solve the problems in their own code so encoding solutions in this way as you write the code is of massive benefit to end users who are at a disadvantage finding solutions since they are often missing information about what exactly the software was doing. Anyone who has ever read an Oracle error message will know what I mean.

The second wonderful thing that comes to mind is when you find yourself trying to describe a solution in your exception and you're writing "Check X and if A then B else C". This is a very clear and obvious sign that your exception is being checked in the wrong place. You the programmer have the capacity to compare things in code so "if" statements should be run in code, why involve the user in something that can be automated? Chances are it's from deeper in the code and someone has done the lazy thing and thrown IOException from any number of methods and caught potential errors from all of them in a block of calling code that cannot adequately describe what went wrong, what the specific context is and how to fix it. This encourages you to write finer grain errors, catch and handle them in the right place in your code so that you can articulate properly the steps the operator should take.

At one company we had top notch operators who got to know the software really well and kept their own "run book" that augmented our error reporting and suggested solutions. To recognise this the software started including wiki links to the run book in exceptions so that a basic explanation was available as well as links to more advanced discussion and observations by the operators over time.

If you've had the dicipline to try this technique, it becomes much more obvious what you should name your exceptions in code when creating your own. NonRecoverableConfigurationReadFailedException becomes a bit of shorthand for what you're about to describe more fully to the operator. I like being verbose and I think that will be easier for the next developer who touches my code to interpret.

Exception Handling – Best Practices for Checked vs Unchecked vs No Exception

In the early days of C++ we discovered that without some sort of generic programming, strongly typed languages were extremely unwieldy. We also discovered that checked exceptions and generic programming didn't work well together, and checked exceptions were essentially abandoned.

Multiset return types are great, but no replacement for exceptions. Without exceptions the code is full of error-checking noise.

The other problem with checked exceptions is that a change in the exceptions thrown by a low-level function forces a cascade of changes in all the callers, and their callers, and so on. The only way to prevent this is for each level of code to catch any exceptions thrown by lower levels and wrap them in a new exception. Again, you end up with very noisy code.

Best Answer

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How to write a good exception message

Exception Handling – Best Practices for Checked vs Unchecked vs No Exception

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