/*
    * $Id: ActionDispatcher.java 471754 2006-11-06 14:55:09Z husted $
    *
    * 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.actions;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.struts.Globals;
  import org.apache.struts.action.Action;
  import org.apache.struts.action.ActionForm;
  import org.apache.struts.action.ActionForward;
  import org.apache.struts.action.ActionMapping;
  import org.apache.struts.util.MessageResources;
  
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  
  import java.util.HashMap;
  
  /**
   * <p>Action <i>helper</i> class that dispatches to a public method in an
   * Action.</p> <p/> <p>This class is provided as an alternative mechanism to
   * using DispatchAction and its various flavours and means <i>Dispatch</i>
   * behaviour can be easily implemented into any <code>Action</code> without
   * having to inherit from a particular super <code>Action</code>.</p> <p/>
   * <p>To implement <i>dispatch</i> behaviour in an <code>Action</code> class,
   * create your custom Action as follows, along with the methods you require
   * (and optionally "cancelled" and "unspecified" methods):</p> <p/>
   * <pre>
   *   public class MyCustomAction extends Action {
   *
   *       protected ActionDispatcher dispatcher
   *                = new ActionDispatcher(this, ActionDispatcher.MAPPING_FLAVOR);
   *
   *       public ActionForward execute(ActionMapping mapping,
   *                                    ActionForm form,
   *                                    HttpServletRequest request,
   *                                    HttpServletResponse response)
   *                           throws Exception {
   *           return dispatcher.execute(mapping, form, request, response);
   *       }
   *   }
   * </pre>
   * <p/>
   *
   * <p>It provides three flavours of determing the name of the method:</p>
   *
   * <ul>
   *
   * <li><strong>{@link #DEFAULT_FLAVOR}</strong> - uses the parameter
   * specified in the struts-config.xml to get the method name from the Request
   * (equivalent to <code>DispatchAction</code> <b>except</b> uses "method" as a
   * default if the <code>parameter</code> is not specified in the
   * struts-config.xml).</li>
   *
   * <li><strong>{@link #DISPATCH_FLAVOR}</strong>
   * - uses the parameter specified in the struts-config.xml to get the method
   * name from the Request (equivalent to <code>DispatchAction</code>).</li>
   *
   * <li><strong>{@link #MAPPING_FLAVOR}</strong> - uses the parameter
   * specified in the struts-config.xml as the method name (equivalent to
   * <code>MappingDispatchAction</code>).</li>
  
   * </ul>
   *
   * @version $Rev: 471754 $ $Date: 2006-11-06 08:55:09 -0600 (Mon, 06 Nov 2006) $
   * @since Struts 1.2.7
   */
  public class ActionDispatcher {
      // ----------------------------------------------------- Instance Variables
  
      /**
       * Indicates "default" dispatch flavor.
       */
      public static final int DEFAULT_FLAVOR = 0;
  
      /**
       * Indicates "mapping" dispatch flavor.
      */
     public static final int MAPPING_FLAVOR = 1;
 
     /**
      * Indicates flavor compatible with DispatchAction.
      */
     public static final int DISPATCH_FLAVOR = 2;
 
     /**
      * Commons Logging instance.
      */
     protected static Log log = LogFactory.getLog(ActionDispatcher.class);
 
     /**
      * The message resources for this package.
      */
     protected static MessageResources messages =
         MessageResources.getMessageResources(
             "org.apache.struts.actions.LocalStrings");
 
     /**
      * The associated Action to dispatch to.
      */
     protected Action actionInstance;
 
     /**
      * Indicates dispatch <i>flavor</i>.
      */
     protected int flavor;
 
     /**
      * The Class instance of this <code>DispatchAction</code> class.
      */
     protected Class clazz;
 
     /**
      * The set of Method objects we have introspected for this class, keyed by
      * method name.  This collection is populated as different methods are
      * called, so that introspection needs to occur only once per method
      * name.
      */
     protected HashMap methods = new HashMap();
 
     /**
      * The set of argument type classes for the reflected method call.  These
      * are the same for all calls, so calculate them only once.
      */
     protected Class[] types =
         {
             ActionMapping.class, ActionForm.class, HttpServletRequest.class,
             HttpServletResponse.class
         };
 
     // ----------------------------------------------------- Constructors
 
     /**
      * Construct an instance of this class from the supplied parameters.
      *
      * @param actionInstance The action instance to be invoked.
      */
     public ActionDispatcher(Action actionInstance) {
         this(actionInstance, DEFAULT_FLAVOR);
     }
 
     /**
      * Construct an instance of this class from the supplied parameters.
      *
      * @param actionInstance The action instance to be invoked.
      * @param flavor         The flavor of dispatch to use.
      */
     public ActionDispatcher(Action actionInstance, int flavor) {
         this.actionInstance = actionInstance;
         this.flavor = flavor;
 
         clazz = actionInstance.getClass();
     }
 
     // --------------------------------------------------------- Public Methods
 
     /**
      * Process the specified HTTP request, and create the corresponding HTTP
      * response (or forward to another web component that will create it).
      * Return an <code>ActionForward</code> instance describing where and how
      * control should be forwarded, or <code>null</code> if the response has
      * already been completed.
      *
      * @param mapping  The ActionMapping used to select this instance
      * @param form     The optional ActionForm bean for this request (if any)
      * @param request  The HTTP request we are processing
      * @param response The HTTP response we are creating
      * @return The forward to which control should be transferred, or
      *         <code>null</code> if the response has been completed.
      * @throws Exception if an exception occurs
      */
     public ActionForward execute(ActionMapping mapping, ActionForm form,
         HttpServletRequest request, HttpServletResponse response)
         throws Exception {
         // Process "cancelled"
         if (isCancelled(request)) {
             ActionForward af = cancelled(mapping, form, request, response);
 
             if (af != null) {
                 return af;
             }
         }
 
         // Identify the request parameter containing the method name
         String parameter = getParameter(mapping, form, request, response);
 
         // Get the method's name. This could be overridden in subclasses.
         String name =
             getMethodName(mapping, form, request, response, parameter);
 
         // Prevent recursive calls
         if ("execute".equals(name) || "perform".equals(name)) {
             String message =
                 messages.getMessage("dispatch.recursive", mapping.getPath());
 
             log.error(message);
             throw new ServletException(message);
         }
 
         // Invoke the named method, and return the result
         return dispatchMethod(mapping, form, request, response, name);
     }
 
     /**
      * <p>Dispatches to the target class' <code>unspecified</code> method, if
      * present, otherwise throws a ServletException. Classes utilizing
      * <code>ActionDispatcher</code> should provide an <code>unspecified</code>
      * method if they wish to provide behavior different than throwing a
      * ServletException.</p>
      *
      * @param mapping  The ActionMapping used to select this instance
      * @param form     The optional ActionForm bean for this request (if any)
      * @param request  The non-HTTP request we are processing
      * @param response The non-HTTP response we are creating
      * @return The forward to which control should be transferred, or
      *         <code>null</code> if the response has been completed.
      * @throws Exception if the application business logic throws an
      *                   exception.
      */
     protected ActionForward unspecified(ActionMapping mapping, ActionForm form,
         HttpServletRequest request, HttpServletResponse response)
         throws Exception {
         // Identify if there is an "unspecified" method to be dispatched to
         String name = "unspecified";
         Method method = null;
 
         try {
             method = getMethod(name);
         } catch (NoSuchMethodException e) {
             String message =
                 messages.getMessage("dispatch.parameter", mapping.getPath(),
                     mapping.getParameter());
 
             log.error(message);
 
             throw new ServletException(message);
         }
 
         return dispatchMethod(mapping, form, request, response, name, method);
     }
 
     /**
      * <p>Dispatches to the target class' cancelled method, if present,
      * otherwise returns null. Classes utilizing <code>ActionDispatcher</code>
      * should provide a <code>cancelled</code> method if they wish to provide
      * behavior different than returning null.</p>
      *
      * @param mapping  The ActionMapping used to select this instance
      * @param form     The optional ActionForm bean for this request (if any)
      * @param request  The non-HTTP request we are processing
      * @param response The non-HTTP response we are creating
      * @return The forward to which control should be transferred, or
      *         <code>null</code> if the response has been completed.
      * @throws Exception if the application business logic throws an
      *                   exception.
      */
     protected ActionForward cancelled(ActionMapping mapping, ActionForm form,
         HttpServletRequest request, HttpServletResponse response)
         throws Exception {
         // Identify if there is an "cancelled" method to be dispatched to
         String name = "cancelled";
         Method method = null;
 
         try {
             method = getMethod(name);
         } catch (NoSuchMethodException e) {
             return null;
         }
 
         return dispatchMethod(mapping, form, request, response, name, method);
     }
 
     // ----------------------------------------------------- Protected Methods
 
     /**
      * Dispatch to the specified method.
      *
      * @param mapping  The ActionMapping used to select this instance
      * @param form     The optional ActionForm bean for this request (if any)
      * @param request  The non-HTTP request we are processing
      * @param response The non-HTTP response we are creating
      * @param name     The name of the method to invoke
      * @return The forward to which control should be transferred, or
      *         <code>null</code> if the response has been completed.
      * @throws Exception if the application business logic throws an
      *                   exception.
      */
     protected ActionForward dispatchMethod(ActionMapping mapping,
         ActionForm form, HttpServletRequest request,
         HttpServletResponse response, String name)
         throws Exception {
         // Make sure we have a valid method name to call.
         // This may be null if the user hacks the query string.
         if (name == null) {
             return this.unspecified(mapping, form, request, response);
         }
 
         // Identify the method object to be dispatched to
         Method method = null;
 
         try {
             method = getMethod(name);
         } catch (NoSuchMethodException e) {
             String message =
                 messages.getMessage("dispatch.method", mapping.getPath(), name);
 
             log.error(message, e);
 
             String userMsg =
                 messages.getMessage("dispatch.method.user", mapping.getPath());
             throw new NoSuchMethodException(userMsg);
         }
 
         return dispatchMethod(mapping, form, request, response, name, method);
     }
 
     /**
      * Dispatch to the specified method.
      *
      * @param mapping  The ActionMapping used to select this instance
      * @param form     The optional ActionForm bean for this request (if any)
      * @param request  The non-HTTP request we are processing
      * @param response The non-HTTP response we are creating
      * @param name     The name of the method to invoke
      * @param method   The method to invoke
      * @return The forward to which control should be transferred, or
      *         <code>null</code> if the response has been completed.
      * @throws Exception if the application business logic throws an
      *                   exception.
      */
     protected ActionForward dispatchMethod(ActionMapping mapping,
         ActionForm form, HttpServletRequest request,
         HttpServletResponse response, String name, Method method)
         throws Exception {
         ActionForward forward = null;
 
         try {
             Object[] args = { mapping, form, request, response };
 
             forward = (ActionForward) method.invoke(actionInstance, args);
         } catch (ClassCastException e) {
             String message =
                 messages.getMessage("dispatch.return", mapping.getPath(), name);
 
             log.error(message, e);
             throw e;
         } catch (IllegalAccessException e) {
             String message =
                 messages.getMessage("dispatch.error", mapping.getPath(), name);
 
             log.error(message, e);
             throw e;
         } catch (InvocationTargetException e) {
             // Rethrow the target exception if possible so that the
             // exception handling machinery can deal with it
             Throwable t = e.getTargetException();
 
             if (t instanceof Exception) {
                 throw ((Exception) t);
             } else {
                 String message =
                     messages.getMessage("dispatch.error", mapping.getPath(),
                         name);
 
                 log.error(message, e);
                 throw new ServletException(t);
             }
         }
 
         // Return the returned ActionForward instance
         return (forward);
     }
 
     /**
      * Introspect the current class to identify a method of the specified name
      * that accepts the same parameter types as the <code>execute</code>
      * method does.
      *
      * @param name Name of the method to be introspected
      * @return The method with the specified name.
      * @throws NoSuchMethodException if no such method can be found
      */
     protected Method getMethod(String name)
         throws NoSuchMethodException {
         synchronized (methods) {
             Method method = (Method) methods.get(name);
 
             if (method == null) {
                 method = clazz.getMethod(name, types);
                 methods.put(name, method);
             }
 
             return (method);
         }
     }
 
     /**
      * <p>Returns the parameter value as influenced by the selected {@link
      * #flavor} specified for this <code>ActionDispatcher</code>.</p>
      *
      * @param mapping  The ActionMapping used to select this instance
      * @param form     The optional ActionForm bean for this request (if any)
      * @param request  The HTTP request we are processing
      * @param response The HTTP response we are creating
      * @return The <code>ActionMapping</code> parameter's value
      * @throws Exception if an error occurs.
      */
     protected String getParameter(ActionMapping mapping, ActionForm form,
         HttpServletRequest request, HttpServletResponse response)
         throws Exception {
         String parameter = mapping.getParameter();
 
         if ("".equals(parameter)) {
             parameter = null;
         }
 
         if ((parameter == null) && (flavor == DEFAULT_FLAVOR)) {
             // use "method" for DEFAULT_FLAVOR if no parameter was provided
             return "method";
         }
 
         if ((parameter == null)
             && ((flavor == MAPPING_FLAVOR) || (flavor == DISPATCH_FLAVOR))) {
             String message =
                 messages.getMessage("dispatch.handler", mapping.getPath());
 
             log.error(message);
 
             throw new ServletException(message);
         }
 
         return parameter;
     }
 
     /**
      * Returns the method name, given a parameter's value.
      *
      * @param mapping   The ActionMapping used to select this instance
      * @param form      The optional ActionForm bean for this request (if
      *                  any)
      * @param request   The HTTP request we are processing
      * @param response  The HTTP response we are creating
      * @param parameter The <code>ActionMapping</code> parameter's name
      * @return The method's name.
      * @throws Exception if an error occurs.
      */
     protected String getMethodName(ActionMapping mapping, ActionForm form,
         HttpServletRequest request, HttpServletResponse response,
         String parameter) throws Exception {
         // "Mapping" flavor, defaults to "method"
         if (flavor == MAPPING_FLAVOR) {
             return parameter;
         }
 
         // default behaviour
         return request.getParameter(parameter);
     }
 
     /**
      * <p>Returns <code>true</code> if the current form's cancel button was
      * pressed.  This method will check if the <code>Globals.CANCEL_KEY</code>
      * request attribute has been set, which normally occurs if the cancel
      * button generated by <strong>CancelTag</strong> was pressed by the user
      * in the current request.  If <code>true</code>, validation performed by
      * an <strong>ActionForm</strong>'s <code>validate()</code> method will
      * have been skipped by the controller servlet.</p>
      *
      * @param request The servlet request we are processing
      * @return <code>true</code> if the current form's cancel button was
      *         pressed; <code>false</code> otherwise.
      * @see org.apache.struts.taglib.html.CancelTag
      */
     protected boolean isCancelled(HttpServletRequest request) {
         return (request.getAttribute(Globals.CANCEL_KEY) != null);
     }
 }