Tuesday, July 15, 2014

Java 8 magic exception copying

Since I can in Java 8 now parameterize constructors as functions, I can write a generic exception copier:

<E extends Throwable>
E copy(final Throwable from, final Function<String, E> ctor) {
    final E to = ctor.apply(from.getMessage());
    for (final Throwable s : from.getSuppressed())
    return to;


try {
    // Something throws
} catch (final AnException | BeException | KatException e) {
    throw copy(e, IOException::new);

This is not a common strategy but one I sometimes use to reduce the incredible size of layered exceptions, especially for logging. It is also handy for shoehorning 3rd-party exceptions into a common framework exception, a nice feature for APIs to simplify calling code. Copy helps reduce boilerplate code.

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