CascadeEvent.java

/*******************************************************************************
 * Copyright (c) 2012-2017 Codenvy, S.A.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Codenvy, S.A. - initial API and implementation
 *******************************************************************************/
package org.eclipse.che.core.db.cascade.event;

import org.eclipse.che.core.db.cascade.CascadeContext;

/**
 * Special event type which is needed only for notification
 * in the process which can require cascade operation.
 *
 * <p>Publisher should invoke {@link #propagateException()}
 * to get cause of event canceling.
 *
 * <p>Rollback of operation must be performed when subscriber
 * throws {@link Exception} during event processing.
 *
 * <p>Usage example:
 * <pre>
 *     EventService bus = new EventService();
 *     bus.subscribe(new CascadeEventSubscriber<MyEvent>() {
 *         @Override
 *         public void onCascadeEvent(MyEvent event) throws Exception {
 *             if (event.getEntityName().startsWith("reserved")) {
 *                 throw new ConflictException("Entity name can't start with `reserved`.");
 *             }
 *         }
 *     });
 *     bus.publish(new MyEvent(...)).propagateException();
 * </pre>
 *
 * @author Anton Korneta
 * @author Sergii Leschenko
 */
public abstract class CascadeEvent {
    protected final CascadeContext context = new CascadeContext();

    public CascadeContext getContext() {
        return context;
    }

    /**
     * Propagates exception if subscriber throws it
     * while event processing otherwise do nothing
     *
     * @throws Exception
     *         when any subscriber throws {@link Exception}
     */
    public void propagateException() throws Exception {
        if (context.isFailed()) {
            throw context.getCause();
        }
    }
}