/*
* $Id: DispatchAction.java 664382 2008-06-07 20:45:12Z pbenedict $
*
* 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.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
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>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>
*
* <p> <code> http://localhost:8080/myapp/saveSubscription.do?method=update
* </code></p>
*
* <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: 664382 $ $Date: 2008-06-07 22:45:12 +0200 (Sam, 07 jui 2008) $
*/
public abstract class DispatchAction extends BaseAction {
/**
* Commons Logging instance.
*/
protected static Log log = LogFactory.getLog(DispatchAction.class);
// ----------------------------------------------------- Instance Variables
/**
* The Class instance of this <code>DispatchAction</code> class.
*/
protected Class clazz = this.getClass();
/**
* 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
* @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 {
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.
*
* @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 {
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.
*
* @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.
* @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.
*
* @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.
* @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());
NoSuchMethodException e2 = new NoSuchMethodException(userMsg);
e2.initCause(e);
throw e2;
}
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
* @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);
}
}
/**
* 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.
* @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);
}
}