net.lshift.accent.ExceptionUtils.java Source code

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Here is the source code for net.lshift.accent.ExceptionUtils.java

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/**
 * Copyright (C) 2011 LShift Ltd.
 *
 * Licensed 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 net.lshift.accent;

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.AlreadyClosedException;
import com.rabbitmq.client.ShutdownSignalException;
import com.rabbitmq.client.impl.AMQImpl;

import java.io.EOFException;
import java.io.IOException;

/**
 * Utilities for diagnosing and working with exceptions.
 */
public class ExceptionUtils {
    /**
     * Attempts to extract a reply code from the given ShutdownSignalException. If a reply code is available, it is
     * returned - otherwise, the method returns 0.
     * @param s the signal to inspect.
     * @return the reply code if available, or 0.
     */
    public static int getReplyCode(ShutdownSignalException s) {
        if (s.getReason() instanceof AMQImpl.Connection.Close) {
            return ((AMQImpl.Connection.Close) s.getReason()).getReplyCode();
        } else {
            return 0;
        }
    }

    /**
     * Determines whether a given shutdown reason is recoverable.
     * @param s the shutdown signal to inspect.
     * @return true - the shutdown is recoverable; false - it isn't.
     */
    public static boolean isShutdownRecoverable(ShutdownSignalException s) {
        if (s != null) {
            int replyCode = getReplyCode(s);

            return s.isInitiatedByApplication()
                    && ((replyCode == AMQP.CONNECTION_FORCED) || (replyCode == AMQP.INTERNAL_ERROR)
                            || s instanceof AlreadyClosedException || (s.getCause() instanceof EOFException));
        }
        return false;
    }

    /**
     * Attempts to execute the given Thunk. If the operation unrecoverably failed, then the exception will be propogated.
     * If the exception can be recovered, then the exception will be simply returned. If the operation succeeds, null
     * will be returned.
     * @param t the operation to attempt.
     * @return the result exception, or null if the operation succeeds.
     * @throws UnrecoverableMessagingException if the operation fails, and cannot be recovered.
     */
    public static Exception attempt(Thunk t) {
        try {
            t.run();
            return null;
        } catch (AlreadyClosedException e) {
            if (isShutdownRecoverable(e)) {
                return e;
            } else {
                throw new UnrecoverableMessagingException(e);
            }
        } catch (IOException e) {
            if (e.getCause() instanceof ShutdownSignalException
                    && !isShutdownRecoverable((ShutdownSignalException) e.getCause())) {
                throw new UnrecoverableMessagingException(e);
            }

            return e;
        }
    }
}