AbstractTemplateView


1   /*
2    * Copyright 2002-2006 the original author or authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package org.springframework.web.servlet.view;
18  
19  import java.util.Enumeration  ;
20  import java.util.Map  ;
21  
22  import javax.servlet.ServletException  ;
23  import javax.servlet.ServletResponse  ;
24  import javax.servlet.http.HttpServletRequest  ;
25  import javax.servlet.http.HttpServletResponse  ;
26  import javax.servlet.http.HttpSession  ;
27  
28  import org.springframework.web.servlet.support.RequestContext;
29  
30  /**
31   * AbstractTemplateView provides template based view technologies such as
32   * Velocity and FreeMarker, with the ability to use request and session
33   * attributes in their model and the option to expose helper objects
34   * for Spring's Velocity/FreeMarker macro library.
35   *
36   * <p>JSP/JSTL and other view technologies automatically have access to the
37   * HttpServletRequest object and thereby the request/session attributes
38   * for the current user. Furthermore, they are able to create and cache
39   * helper objects as request attributes themselves.
40   *
41   * @author Darren Davison
42   * @author Juergen Hoeller
43   * @since 1.0.2
44   */
45  public abstract class AbstractTemplateView extends AbstractUrlBasedView {
46  
47      /**
48       * Variable name of the RequestContext instance in the template model,
49       * available to Spring's macros: e.g. for creating BindStatus objects.
50       */
51      public static final String   SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE = "springMacroRequestContext";
52  
53  
54      private static boolean responseGetContentTypeAvailable;
55  
56      static {
57          // Determine whether the Servlet 2.4 ServletResponse.getContentType method
58          // is available.
59          try {
60              ServletResponse  .class.getMethod("getContentType", new Class  [] {});
61              responseGetContentTypeAvailable = true;
62          }
63          catch (NoSuchMethodException   ex) {
64              responseGetContentTypeAvailable = false;
65          }
66      }
67  
68      private boolean exposeRequestAttributes = false;
69  
70      private boolean exposeSessionAttributes = false;
71  
72      private boolean exposeSpringMacroHelpers = false;
73      
74      private boolean allowRequestOverride = false;
75      
76      private boolean allowSessionOverride = false;
77  
78  
79      /**
80       * Set whether all request attributes should be added to the
81       * model prior to merging with the template. Default is "false".
82       */
83      public void setExposeRequestAttributes(boolean exposeRequestAttributes) {
84          this.exposeRequestAttributes = exposeRequestAttributes;
85      }
86  
87      /**
88       * Set whether all HttpSession attributes should be added to the
89       * model prior to merging with the template. Default is "false".
90       */
91      public void setExposeSessionAttributes(boolean exposeSessionAttributes) {
92          this.exposeSessionAttributes = exposeSessionAttributes;
93      }
94  
95      /**
96       * Set whether HttpServletRequest attributes are allowed to override (hide)
97       * controller generated model attributes of the same name. Default is "false",
98       * which causes an exception to be thrown if request attributes of the same
99       * name as model attributes are found.
100      */
101     public void setAllowRequestOverride(boolean allowRequestOverride) {
102         this.allowRequestOverride = allowRequestOverride;
103     }
104     
105     /**
106      * Set whether HttpSession attributes are allowed to override (hide)
107      * controller generated model attributes of the same name. Default is "false",
108      * which causes an exception to be thrown if session attributes of the same
109      * name as model attributes are found.
110      */
111     public void setAllowSessionOverride(boolean allowSessionOverride) {
112         this.allowSessionOverride = allowSessionOverride;
113     }
114 
115     /**
116      * Set whether to expose a RequestContext for use by Spring's macro library,
117      * under the name "springMacroRequestContext". Default is "false".
118      * <p>Currently needed for Spring's Velocity and FreeMarker default macros.
119      * Note that this is <b>not</b> required for templates that use HTML
120      * forms <b>unless</b> you wish to take advantage of the Spring helper macros.
121      * @see #SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE
122      */
123     public void setExposeSpringMacroHelpers(boolean exposeSpringMacroHelpers) {
124         this.exposeSpringMacroHelpers = exposeSpringMacroHelpers;
125     }
126 
127 
128     protected final void renderMergedOutputModel(
129             Map   model, HttpServletRequest   request, HttpServletResponse   response) throws Exception   {
130 
131         if (this.exposeRequestAttributes) {
132             for (Enumeration   en = request.getAttributeNames(); en.hasMoreElements();) {
133                 String   attribute = (String  ) en.nextElement();
134                 if (model.containsKey(attribute) && !this.allowRequestOverride) {
135                     throw new ServletException  ("Cannot expose request attribute '" + attribute +
136                         "' because of an existing model object of the same name");
137                 }
138                 Object   attributeValue = request.getAttribute(attribute);
139                 if (logger.isDebugEnabled()) {
140                     logger.debug("Exposing request attribute '" + attribute +
141                             "' with value [" + attributeValue + "] to model");
142                 }
143                 model.put(attribute, attributeValue);
144             }
145         }
146 
147         if (this.exposeSessionAttributes) {
148             HttpSession   session = request.getSession(false);
149             if (session != null) {
150                 for (Enumeration   en = session.getAttributeNames(); en.hasMoreElements();) {
151                     String   attribute = (String  ) en.nextElement();
152                     if (model.containsKey(attribute) && !this.allowSessionOverride) {
153                         throw new ServletException  ("Cannot expose session attribute '" + attribute +
154                             "' because of an existing model object of the same name");
155                     }
156                     Object   attributeValue = session.getAttribute(attribute);
157                     if (logger.isDebugEnabled()) {
158                         logger.debug("Exposing session attribute '" + attribute +
159                                 "' with value [" + attributeValue + "] to model");
160                     }
161                     model.put(attribute, attributeValue);
162                 }
163             }
164         }
165 
166         if (this.exposeSpringMacroHelpers) {
167             if (model.containsKey(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE)) {
168                 throw new ServletException  (
169                         "Cannot expose bind macro helper '" + SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE +
170                         "' because of an existing model object of the same name");
171             }
172             // expose RequestContext instance for Spring macros
173             model.put(SPRING_MACRO_REQUEST_CONTEXT_ATTRIBUTE, new RequestContext(request, model));
174         }
175 
176         applyContentType(response);
177 
178         renderMergedTemplateModel(model, request, response);
179     }
180 
181     /**
182      * Apply this view's content type as specified in the "contentType"
183      * bean property to the given response.
184      * <p>When running on Servlet 2.4, only applies the view's contentType
185      * if no content type has been set on the response before. This allows
186      * handlers to override the default content type beforehand.
187      * @param response current HTTP response
188      * @see #setContentType
189      */
190     protected void applyContentType(HttpServletResponse   response)   {
191         if (!responseGetContentTypeAvailable || response.getContentType() == null) {
192             response.setContentType(getContentType());
193         }
194     }
195 
196     /**
197      * Subclasses must implement this method to actually render the view.
198      * @param model combined output Map, with request attributes and
199      * session attributes merged into it if required
200      * @param request current HTTP request
201      * @param response current HTTP response
202      * @throws Exception if rendering failed
203      */
204     protected abstract void renderMergedTemplateModel(
205             Map   model, HttpServletRequest   request, HttpServletResponse   response) throws Exception  ;
206 
207 }
208
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