Question

I’m refactoring some code to use guava Cache.

Initial code:

public Post getPost(Integer key) throws SQLException, IOException {
    return PostsDB.findPostByID(key);
}

In order not to break something I need to preserve any thrown exception as is, without wrapping it.

Current solution appears somewhat ugly:

public Post getPost(final Integer key) throws SQLException, IOException {
    try {
        return cache.get(key, new Callable<Post>() {
            @Override
            public Post call() throws Exception {
                return PostsDB.findPostByID(key);
            }
        });
    } catch (ExecutionException e) {
        Throwable cause = e.getCause();
        if (cause instanceof SQLException) {
            throw (SQLException) cause;
        } else if (cause instanceof IOException) {
            throw (IOException) cause;
        } else if (cause instanceof RuntimeException) {
            throw (RuntimeException) cause;
        } else if (cause instanceof Error) {
            throw (Error) cause;
        } else {
            throw new IllegalStateException(e);
        }
    }
}

Is there any possible way to make it nicer?

Answer 1

Just after writing the question started thinking about utility method powered with generics.
Then remembered something about Throwables.
And yes, it’s already there! )

It may also be necessary to handle UncheckedExecutionException or even ExecutionError.

So the solution is:

public Post getPost(final Integer key) throws SQLException, IOException {
    try {
        return cache.get(key, new Callable<Post>() {
            @Override
            public Post call() throws Exception {
                return PostsDB.findPostByID(key);
            }
        });
    } catch (ExecutionException e) {
        Throwables.propagateIfPossible(
            e.getCause(), SQLException.class, IOException.class);
        throw new IllegalStateException(e);
    } catch (UncheckedExecutionException e) {
        Throwables.throwIfUnchecked(e.getCause());
        throw new IllegalStateException(e);
    }
}

Very nice!

See also ThrowablesExplained, LoadingCache.getUnchecked and Why we deprecated Throwables.propagate.