番石榴缓存并保留已检查的异常

Question

我正在重构一些使用番石榴缓存的代码.

初始代码:

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

为了不破坏某些东西,我需要保留任何抛出的异常,而不包装它.

目前的解决方案看起来有些难看

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);
        }
    }
}

有没有办法让它变得更好？

Answer 1

在写完问题之后,开始考虑使用泛型的实用方法.然后想起了关于Throwables的一些事情.是的,它已经存在了!)

可能还需要处理UncheckedExecutionException甚至ExecutionError.

所以解决方案是:

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);
    }
}

非常好!

另请参阅ThrowablesExplained,LoadingCache.getUnchecked以及我们为何弃用Throwables.propagate.