/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.waveprotocol.box.server.waveserver;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
/**
* Utility methods for futures.
*
* @author soren@google.com (Soren Lassen)
*/
public class FutureUtil {
/**
* Wraps an unexpected exception as a {@link RuntimeException}.
*/
public static class UnexpectedExceptionFromFuture extends RuntimeException {
public UnexpectedExceptionFromFuture(Throwable cause) {
super(cause);
}
}
/**
* Gets the result of the given future or propagates any exception of
* the expected type. That is, in the case of an {@link ExecutionException}),
* if the cause has the expected type, it is unwrapped and thrown directly.
*
* @param <V> the result type of the future
* @param <X> exception type expected to be wrapped
* @param future future to check
* @param expectedCauseClass class of exception expected to be wrapped
* @return the result of the future
* @throws X if the future throws an {@link ExecutionException} wrapping an
* exception of type X
* @throws UnexpectedExceptionFromFuture wrapping any cause of
* an {@link ExecutionException} not of type X
* @throws InterruptedException if the current thread was interrupted
* @throws CancellationException if the future was cancelled
*/
public static <V, X extends Exception> V getResultOrPropagateException(Future<V> future,
Class<X> expectedCauseClass) throws X, InterruptedException {
try {
return future.get();
} catch (ExecutionException e) {
Throwable cause = e.getCause();
if (expectedCauseClass.isInstance(cause)) {
throw expectedCauseClass.cast(cause);
} else {
throw new UnexpectedExceptionFromFuture(cause);
}
}
}
private FutureUtil() { } // prevent instantiation
}