@PostConstruct & Checked exceptions

Question

In the @PostConstruct doc it says about the annotated methods:

"The method MUST NOT throw a checked exception."

How would one deal with e.g. an IOException which can be thrown in such a method? Just wrap it in a RuntimeException and let the user worry about the faulty initial state of the object? Or is @PostConstruct the wrong place to validate and initialize objects which got their dependencies injected?

Frustule

Interesting, I hadn't noticed that. Seems like an odd restriction, given that the method is called reflectively. – Offbeat

PostConstruct method is for initializing objects. Why would you put something that throws IOException in an initialize method? – Maurits

@Medopal: I'm checking for the existence of DB tables in the init method of a service, which throws IOException – Frustule

@medopal redirecting or sending an HTTP error code also throw IOException – Rating

Is this constraint mostly from a philosophical viewpoint as in Exception must not be thrown while initializing objects or there is a bigger practical issue attached to it? I didn't fully understand this part why PostConstruct must not throw a checked exception – Protractile

Answer 1

Yes, wrap it in a runtime exception. Preferebly something more concrete like IllegalStateException.

Note that if the init method fails, normally the application won't start.

Schott

Answer 2

Generally, if you want or expect application start-up failure when one of your beans throws an exception you can use Lombok's @SneakyThrows.

It is incredibly useful and succinct when used correctly:

@SneakyThrows
@PostConstruct
public void init() {
    // I usually throw a checked exception
}

There's a recent write-up discussing its pros and cons here: Prefer Lombok’s @SneakyThrows to rethrowing checked exceptions as RuntimeExceptions

Enjoy!

Underclay

You can have similar effect without using Lombok. Assuming you throw SomeCheckedException in your init method you could write public void init() throws SomeCheckedException { and result should be the same as with Lombok @SneakyThrows. – Lewan

Answer 3

Use a softened exception like so, in effect wrapping in RuntimeException:

private static RuntimeException softenException(Exception e) {
    return new RuntimeException("Softened exception.", e);
}

Then usage is like:

} catch (IOException e) {
        throw softenException(e);
}

Tadzhik

How can this work? From what I see, you cannot just take an arbitrary exception and cast it to a RuntimeException. Sure the code will compile, but have you tried running this on the said IOException? I'm pretty sure you'll get a ClassCastException due to the fact that IOException does not inherit from RuntimeException. To truly get a RuntimeException you have to wrap the original exception in a new instance of RuntimeException or a subclass of choice. – Singlehandedly

Yeah, my code doesn't work right, but hopeully the basic idea, as you can see, is possible. – Tadzhik