action.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.action;

import org.apache.struts.Globals;
import org.apache.struts.config.ModuleConfig;
import org.apache.struts.util.MessageResources;
import org.apache.struts.util.ModuleUtils;
import org.apache.struts.util.RequestUtils;
import org.apache.struts.util.TokenProcessor;

import javax.servlet.ServletContext;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import java.util.Locale;

/**
 * <p>An <strong>Action</strong> is an adapter between the contents of an
 * incoming HTTP request and the corresponding business logic that should be
 * executed to process this request. The controller (RequestProcessor) will
 * select an appropriate Action for each request, create an instance (if
 * necessary), and call the <code>execute</code> method.</p>
 *
 * <p>Actions must be programmed in a thread-safe manner, because the
 * controller will share the same instance for multiple simultaneous requests.
 * This means you should design with the following items in mind: </p>
 *
 * <ul>
 *
 * <li>Instance and static variables MUST NOT be used to store information
 * related to the state of a particular request. They MAY be used to share
 * global resources across requests for the same action.</li>
 *
 * <li>Access to other resources (JavaBeans, session variables, etc.) MUST be
 * synchronized if those resources require protection. (Generally, however,
 * resource classes should be designed to provide their own protection where
 * necessary.</li>
 *
 * </ul>
 *
 * <p>When an <code>Action</code> instance is first created, the controller
 * will call <code>setServlet</code> with a non-null argument to identify the
 * servlet instance to which this Action is attached. When the servlet is to
 * be shut down (or restarted), the <code>setServlet</code> method will be
 * called with a <code>null</code> argument, which can be used to clean up any
 * allocated resources in use by this Action.</p>
 *
 * @version $Rev$ $Date: 2005-08-26 21:58:39 -0400 (Fri, 26 Aug 2005)
 *          $
 */
public class Action {
    /**
     * <p>An instance of <code>TokenProcessor</code> to use for token
     * functionality.</p>
     */
    private static TokenProcessor token = TokenProcessor.getInstance();
    
    /**
     * The action execution was a failure. Show an error view, possibly asking
     * the user to retry entering data.
     * 
     * @since Struts 1.4
     */
    public static final String ERROR = "error";

    /**
     * The action execution require more input in order to succeed. This 
     * result is typically used if a form handling action has been executed 
     * so as to provide defaults for a form. The form associated with the 
     * handler should be shown to the end user.
     * <p>
     * This result is also used if the given input params are invalid, 
     * meaning the user should try providing input again. 
     * 
     * @since Struts 1.4
     */
    public static final String INPUT = "input";
    
    /**
     * The action could not execute, since the user most was not logged in. 
     * The login view should be shown.
     * 
     * @since Struts 1.4
     */
    public static final String LOGIN = "login";

    /**
     * The action execution was successful. Show result view to the end user.
     * 
     * @since Struts 1.4
     */
    public static final String SUCCESS = "success";
    
    // NOTE: We can make the tken  variable protected and remove Action's
    // token methods or leave it private and allow the token methods to
    // delegate their calls.
    // ----------------------------------------------------- Instance Variables

    /**
     * <p>The servlet to which we are attached.</p>
     */
    protected transient ActionServlet servlet = null;

    // ------------------------------------------------------------- Properties

    /**
     * <p>Return the servlet instance to which we are attached.</p>
     *
     * @return The servlet instance to which we are attached.
     */
    public ActionServlet getServlet() {
        return (this.servlet);
    }

    /**
     * <p>Set the servlet instance to which we are attached (if
     * <code>servlet</code> is non-null), or release any allocated resources
     * (if <code>servlet</code> is null).</p>
     *
     * @param servlet The new controller servlet, if any
     */
    public void setServlet(ActionServlet servlet) {
        this.servlet = servlet;

        // :FIXME: Is this suppose to release resources?
    }

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

    /**
     * <p>Process the specified non-HTTP request, and create the corresponding
     * non-HTTP response (or forward to another web component that will create
     * it), with provision for handling exceptions thrown by the business
     * logic. Return an {@link ActionForward} instance describing where and
     * how control should be forwarded, or <code>null</code> if the response
     * has already been completed.</p>
     *
     * <p>The default implementation attempts to forward to the HTTP version
     * of this method.</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.
     * @since Struts 1.1
     */
    public ActionForward execute(ActionMapping mapping, ActionForm form,
        ServletRequest request, ServletResponse response)
        throws Exception {
        try {
            return execute(mapping, form, (HttpServletRequest) request,
                (HttpServletResponse) response);
        } catch (ClassCastException e) {
            return null;
        }
    }

    /**
     * <p>Process the specified HTTP request, and create the corresponding
     * HTTP response (or forward to another web component that will create
     * it), with provision for handling exceptions thrown by the business
     * logic. Return an {@link ActionForward} instance describing where and
     * how control should be forwarded, or <code>null</code> if the response
     * has already been completed.</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 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
     */
    public ActionForward execute(ActionMapping mapping, ActionForm form,
        HttpServletRequest request, HttpServletResponse response)
        throws Exception {
        return null;
    }

    // ---------------------------------------------------- Protected Methods

    /**
     * Adds the specified messages keys into the appropriate request attribute
     * for use by the &lt;html:messages&gt; tag (if messages="true" is set),
     * if any messages are required. Initialize the attribute if it has not
     * already been. Otherwise, ensure that the request attribute is not set.
     *
     * @param request  The servlet request we are processing
     * @param messages Messages object
     * @since Struts 1.2.1
     */
    protected void addMessages(HttpServletRequest request,
        ActionMessages messages) {
        if (messages == null) {
            //  bad programmer! *slap*
            return;
        }

        // get any existing messages from the request, or make a new one
        ActionMessages requestMessages =
            (ActionMessages) request.getAttribute(Globals.MESSAGE_KEY);

        if (requestMessages == null) {
            requestMessages = new ActionMessages();
        }

        // add incoming messages
        requestMessages.add(messages);

        // if still empty, just wipe it out from the request
        if (requestMessages.isEmpty()) {
            request.removeAttribute(Globals.MESSAGE_KEY);

            return;
        }

        // Save the messages
        request.setAttribute(Globals.MESSAGE_KEY, requestMessages);
    }

    /**
     * Adds the specified errors keys into the appropriate request attribute
     * for use by the &lt;html:errors&gt; tag, if any messages are required.
     * Initialize the attribute if it has not already been. Otherwise, ensure
     * that the request attribute is not set.
     *
     * @param request The servlet request we are processing
     * @param errors  Errors object
     * @since Struts 1.2.1
     */
    protected void addErrors(HttpServletRequest request, ActionMessages errors) {
        if (errors == null) {
            //  bad programmer! *slap*
            return;
        }

        // get any existing errors from the request, or make a new one
        ActionMessages requestErrors =
            (ActionMessages) request.getAttribute(Globals.ERROR_KEY);

        if (requestErrors == null) {
            requestErrors = new ActionMessages();
        }

        // add incoming errors
        requestErrors.add(errors);

        // if still empty, just wipe it out from the request
        if (requestErrors.isEmpty()) {
            request.removeAttribute(Globals.ERROR_KEY);

            return;
        }

        // Save the errors
        request.setAttribute(Globals.ERROR_KEY, requestErrors);
    }

    /**
     * <p>Generate a new transaction token, to be used for enforcing a single
     * request for a particular transaction.</p>
     *
     * @param request The request we are processing
     * @return The new transaction token.
     */
    protected String generateToken(HttpServletRequest request) {
        return token.generateToken(request);
    }