com.eucalyptus.loadbalancing.activities.EventHandlerChain.java Source code

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Here is the source code for com.eucalyptus.loadbalancing.activities.EventHandlerChain.java

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/*************************************************************************
 * Copyright 2009-2013 Eucalyptus Systems, Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see http://www.gnu.org/licenses/.
 *
 * Please contact Eucalyptus Systems, Inc., 6755 Hollister Ave., Goleta
 * CA 93117, USA or visit http://www.eucalyptus.com/licenses/ if you need
 * additional information or have any questions.
 ************************************************************************/
package com.eucalyptus.loadbalancing.activities;

import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;

import org.apache.log4j.Logger;
import com.google.common.collect.Lists;

/**
 * @author Sang-Min Park (spark@eucalyptus.com)
 *
 */
public abstract class EventHandlerChain<T extends LoadbalancingEvent> {
    private static Logger LOG = Logger.getLogger(EventHandlerChain.class);
    private final List<EventHandler<T>> handlers = Lists.newArrayList();

    protected void insert(EventHandler<T> next) {
        handlers.add(next);
    }

    public void execute(T evt) throws EventHandlerChainException {
        LinkedList<EventHandler<T>> reverseHandler = Lists.newLinkedList();
        for (EventHandler<T> handler : this.handlers) {
            try {
                reverseHandler.addFirst(handler); // failed handler will rollback too
                handler.apply(evt);
                if (handler.skipRemaining()) {
                    LOG.info("skipping the remaining handlers");
                    break;
                }
            } catch (Exception e) {
                LOG.warn("starting to rollback");
                final String msg = e.getMessage() != null ? e.getMessage()
                        : String.format("failed handling %s at %s", evt, handler);
                final EventHandlerChainException toThrow = new EventHandlerChainException(msg, e, true);
                for (EventHandler<T> h : reverseHandler) {
                    try {
                        h.rollback();
                    } catch (Exception ex) {
                        LOG.warn("rollback failed at " + h.toString(), ex);
                        toThrow.setRollback(false); // fail once, rollback status is set to false
                    }
                }
                LOG.info("finished rollback");
                throw toThrow;
            }
        }
    }

    public abstract EventHandlerChain<T> build();

    @SuppressWarnings("unchecked")
    public <HT> HT findHandler(Class<HT> handlerType) {
        for (EventHandler<T> handler : this.handlers) {
            if (handler.getClass().isAssignableFrom(handlerType)) {
                return (HT) handler;
            }
        }
        throw new NoSuchElementException();
    }
}