executecommand.java.svn-base

MVC开源框架

/*
 * $Id$
 *
 * 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.apache.struts.chain.commands;

import org.apache.commons.chain.Catalog;
import org.apache.commons.chain.CatalogFactory;
import org.apache.commons.chain.Command;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.struts.chain.contexts.ActionContext;
import org.apache.struts.config.ActionConfig;

/**
 * <p>Invoke the appropriate <code>Command</code> for this request.  If the
 * context's <code>ActionConfig</code> has no <code>command</code> property
 * defined, no action will be taken.  If the specified command cannot be
 * found, a warning will be logged, but processing will continue.  Depending
 * on how the chain is configured, this can be used in place of an
 * <code>Action</code> or as a method of performing pre-processing. </p>
 *
 * <p>If used instead of an action, the command which is looked up should put
 * an ActionForward into the context, unless it has already dealt with the
 * response.</p>
 *
 * @version $Id$
 */
public class ExecuteCommand extends ActionCommandBase {
    // ------------------------------------------------------ Instance Variables

    /**
     * Provide Commons Logging instance for this class.
     */
    private static final Log LOG = LogFactory.getLog(ExecuteCommand.class);

    // ---------------------------------------------------------- Public Methods

    /**
     * <p>If the <code>context</code> is "valid", lookup a command and execute
     * it.</p>
     *
     * @param actionCtx The <code>Context</code> for the current request
     * @return the result of the lookup command's <code>execute</code> method,
     *         if executed, or <code>false</code> if it was not executed.
     * @throws Exception on any error
     */
    public boolean execute(ActionContext actionCtx)
        throws Exception {
        if (shouldProcess(actionCtx)) {
            Command command = getCommand(actionCtx);

            if (command != null) {
                return (command.execute(actionCtx));
            }
        }

        return (false);
    }

    /**
     * <p>Evaluate the current context to see if a command should even be
     * executed.</p>
     *
     * @param context A valid ActionContext
     * @return TRUE if the pending Command should be executed
     */
    protected boolean shouldProcess(ActionContext context) {
        // Skip processing if the current request is not valid
        Boolean valid = context.getFormValid();

        return ((valid != null) && valid.booleanValue());
    }

    /**
     * <p>Find the <code>ActionConfig</code> in the current context and, if it
     * is properly configured, lookup the appropriate <code>commons-chain</code>
     * command.</p>
     *
     * @param context A valid ActionContext
     * @return a <code>Command</code> to execute, or null if none is specified
     *         or if the specified command cannot be found.
     */
    protected Command getCommand(ActionContext context) {
        ActionConfig actionConfig = context.getActionConfig();

        String commandName = actionConfig.getCommand();

        if (commandName == null) {
            return null;
        }

        String catalogName = actionConfig.getCatalog();

        return getCommand(commandName, catalogName);
    }

    /**
     * <p> Retrieve the specified Command from the specified Catalog. </p>
     *
     * @param commandName The Command to retrieve.
     * @param catalogName The Catalog to search.
     * @return Instantiated Command, or null
     */
    protected Command getCommand(String commandName, String catalogName) {
        if (commandName == null) {
            return null;
        }

        Catalog catalog;

        if (catalogName != null) {
            catalog = CatalogFactory.getInstance().getCatalog(catalogName);

            if (catalog == null) {
                LOG.warn("When looking up " + commandName + ","
                    + " no catalog found under " + catalogName);

                return null;
            }
        } else {
            catalogName = "the default catalog";
            catalog = CatalogFactory.getInstance().getCatalog();

            if (catalog == null) {
                LOG.warn("When looking up " + commandName + ","
                    + " no default catalog found.");

                return null;
            }
        }

        if (LOG.isDebugEnabled()) {
            LOG.debug("looking up command " + commandName + " in "
                + catalogName);
        }

        return catalog.getCommand(commandName);
    }
}