@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?

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.

Answer 2

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);
}

Answer 3

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!