alma.acs.nc.sm.generic.AcsScxmlDispatchingAction.java Source code

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/*******************************************************************************
 * ALMA - Atacama Large Millimeter Array
 * Copyright (c) ESO - European Southern Observatory, 2011
 * (in the framework of the ALMA collaboration).
 * All rights reserved.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
 *******************************************************************************/
package alma.acs.nc.sm.generic;

import java.util.Collection;

import org.apache.commons.logging.Log;
import org.apache.commons.scxml.ErrorReporter;
import org.apache.commons.scxml.EventDispatcher;
import org.apache.commons.scxml.SCInstance;
import org.apache.commons.scxml.SCXMLExpressionException;
import org.apache.commons.scxml.model.Action;
import org.apache.commons.scxml.model.ModelException;
import org.apache.commons.scxml.semantics.ErrorConstants;

/**
 * Action implementation class to be instantiated by the SCXML framework.
 * Forwards the execute call to the user-supplied dispatcher,
 * from where it goes to user-instantiated action impl objects.
 * <p>
 * The idea is to overcome Apache SCXML's limitation that action handlers 
 * cannot be injected, but instead get created by the framwork.
 * This allows flexible implementation of one or many actions in one class,
 * the use of normal JDK/ACS loggers in the action code, 
 * and flexibility in how the action objects can delegate among themselves
 * and to other objects.
 * 
 * @author hsommer
 */
public class AcsScxmlDispatchingAction<E extends Enum<E>> extends Action {

    /** Serial version UID. */
    private static final long serialVersionUID = 1L;

    /**
     * Set by the framework right after construction, via {@link #setName(String)}.
     * This mechanism is based on beanutils, working with SCXML elements such as 
     * &lt;customActionDomain:createEnvironment name="createEnvironment"/&gt;
     * that have a name attribute.
     */
    private String actionName;

    /**
     * The enum version of {@link #actionName}. 
     * Only available after the first call to {@link #getActionDispatcher(SCInstance)}
     * because we need the concrete enum class for the String-enum conversion,
     * which is only available through the user-supplied dispatcher.
     */
    private E action;

    /**
     * Cache, see {@link #getActionDispatcher(SCInstance)}.
     */
    private volatile AcsScxmlActionDispatcher<E> disp;

    /**
     * Called by the SCXML framework
     */
    public AcsScxmlDispatchingAction() {
    }

    /**
     * Gets the action name.
     * 
     * @return Returns the name.
     */
    public String getName() {
        return actionName;
    }

    /**
     * Sets the name. Stores it in {@link #actionName}.
     */
    public void setName(String name) {
        actionName = name;
    }

    //   @SuppressWarnings("rawtypes")
    public void execute(final EventDispatcher evtDispatcher, final ErrorReporter errRep,
            final SCInstance scInstance, final Log appLog, final Collection derivedEvents)
            throws ModelException, SCXMLExpressionException {

        try {
            getActionDispatcher(scInstance);
        } catch (Exception ex) {
            errRep.onError(ErrorConstants.UNDEFINED_VARIABLE,
                    "Failed to get UserActionDispatcher object from root context.", ex);
        }

        if (disp != null && action != null) {
            // forward the action call to the dispatcher
            disp.execute(action, evtDispatcher, errRep, scInstance, derivedEvents);
        } else {
            errRep.onError(ErrorConstants.UNDEFINED_VARIABLE,
                    "Failed to get UserActionDispatcher object from root context.", null);
        }
    }

    /**
     * Retrieves the user-supplied action dispatcher from the sm root context and
     * caches it in {@link #disp}. 
     * @param scInstance
     */
    private void getActionDispatcher(SCInstance scInstance) {
        if (disp == null) {
            synchronized (this) {
                if (disp == null) {
                    disp = (AcsScxmlActionDispatcher<E>) scInstance.getRootContext()
                            .get(AcsScxmlActionDispatcher.class.getName());
                    // cache the action enum
                    action = Enum.valueOf(disp.getActionType(), this.actionName);
                }
            }
        }
    }
}