Java tutorial
/* * $Id: DispatchAction.java 384089 2006-03-08 01:50:52Z niallp $ * * Copyright 2001-2006 The Apache Software Foundation. * * Licensed 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 java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.HashMap; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; 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; /** * <p>An abstract <strong>Action</strong> that dispatches to a public * method that is named by the request parameter whose name is specified * by the <code>parameter</code> property of the corresponding * ActionMapping. This Action is useful for developers who prefer to * combine many similar actions into a single Action class, in order to * simplify their application design.</p> * * <p>To configure the use of this action in your * <code>struts-config.xml</code> file, create an entry like this:</p> * * <code> * <action path="/saveSubscription" * type="org.apache.struts.actions.DispatchAction" * name="subscriptionForm" * scope="request" * input="/subscription.jsp" * parameter="method"/> * </code> * * <p>which will use the value of the request parameter named "method" * to pick the appropriate "execute" method, which must have the same * signature (other than method name) of the standard Action.execute * method. For example, you might have the following three methods in the * same action:</p> * <ul> * <li>public ActionForward delete(ActionMapping mapping, ActionForm form, * HttpServletRequest request, HttpServletResponse response) * throws Exception</li> * <li>public ActionForward insert(ActionMapping mapping, ActionForm form, * HttpServletRequest request, HttpServletResponse response) * throws Exception</li> * <li>public ActionForward update(ActionMapping mapping, ActionForm form, * HttpServletRequest request, HttpServletResponse response) * throws Exception</li> * </ul> * <p>and call one of the methods with a URL like this:</p> * <code> * http://localhost:8080/myapp/saveSubscription.do?method=update * </code> * * <p><strong>NOTE</strong> - All of the other mapping characteristics of * this action must be shared by the various handlers. This places some * constraints over what types of handlers may reasonably be packaged into * the same <code>DispatchAction</code> subclass.</p> * * <p><strong>NOTE</strong> - If the value of the request parameter is empty, * a method named <code>unspecified</code> is called. The default action is * to throw an exception. If the request was cancelled (a <code>html:cancel</code> * button was pressed), the custom handler <code>cancelled</code> will be used instead. * You can also override the <code>getMethodName</code> method to override the action's * default handler selection.</p> * * @version $Rev: 384089 $ $Date: 2006-03-08 01:50:52 +0000 (Wed, 08 Mar 2006) $ */ public abstract class DispatchAction extends Action { // ----------------------------------------------------- Instance Variables /** * The Class instance of this <code>DispatchAction</code> class. */ protected Class clazz = this.getClass(); /** * Commons Logging instance. */ protected static Log log = LogFactory.getLog(DispatchAction.class); /** * The message resources for this package. */ protected static MessageResources messages = MessageResources .getMessageResources("org.apache.struts.actions.LocalStrings"); /** * 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 }; // --------------------------------------------------------- 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 * * @exception Exception if an exception occurs */ public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { if (isCancelled(request)) { ActionForward af = cancelled(mapping, form, request, response); if (af != null) { return af; } } // Get the parameter. This could be overridden in subclasses. 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); } /** * Method which is dispatched to when there is no value for specified * request parameter included in the request. Subclasses of * <code>DispatchAction</code> should override this method if they wish * to provide default behavior different than throwing a ServletException. */ protected ActionForward unspecified(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { String message = messages.getMessage("dispatch.parameter", mapping.getPath(), mapping.getParameter()); log.error(message); throw new ServletException(message); } /** * Method which is dispatched to when the request is a cancel button submit. * Subclasses of <code>DispatchAction</code> should override this method if * they wish to provide default behavior different than returning null. * @since Struts 1.2.0 */ protected ActionForward cancelled(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { return null; } // ----------------------------------------------------- Protected Methods /** * Dispatch to the specified method. * @since Struts 1.1 */ 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); } ActionForward forward = null; try { Object args[] = { mapping, form, request, response }; forward = (ActionForward) method.invoke(this, 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); } /** * <p>Returns the parameter value.</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 the parameter is missing. */ protected String getParameter(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { // Identify the request parameter containing the method name String parameter = mapping.getParameter(); if (parameter == null) { String message = messages.getMessage("dispatch.handler", mapping.getPath()); log.error(message); throw new ServletException(message); } return parameter; } /** * 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 * * @exception 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); } } /** * 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. * @since Struts 1.2.0 */ protected String getMethodName(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response, String parameter) throws Exception { // Identify the method name to be dispatched to. // dispatchMethod() will call unspecified() if name is null return request.getParameter(parameter); } }