OncePerRequestFilter


1   /*
2    * Copyright 2002-2007 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.filter;
18  
19  import java.io.IOException  ;
20  
21  import javax.servlet.FilterChain  ;
22  import javax.servlet.ServletException  ;
23  import javax.servlet.ServletRequest  ;
24  import javax.servlet.ServletResponse  ;
25  import javax.servlet.http.HttpServletRequest  ;
26  import javax.servlet.http.HttpServletResponse  ;
27  
28  /**
29   * Filter base class that guarantees to be just executed once per request,
30   * on any servlet container. It provides a {@link #doFilterInternal}
31   * method with HttpServletRequest and HttpServletResponse arguments.
32   *
33   * <p>The {@link #getAlreadyFilteredAttributeName} method determines how
34   * to identify that a request is already filtered. The default implementation
35   * is based on the configured name of the concrete filter instance.
36   *
37   * @author Juergen Hoeller
38   * @since 06.12.2003
39   */
40  public abstract class OncePerRequestFilter extends GenericFilterBean {
41  
42      /**
43       * Suffix that gets appended to the filter name for the
44       * "already filtered" request attribute.
45       * @see #getAlreadyFilteredAttributeName
46       */
47      public static final String   ALREADY_FILTERED_SUFFIX = ".FILTERED";
48  
49  
50      /**
51       * This <code>doFilter</code> implementation stores a request attribute for
52       * "already filtered", proceeding without filtering again if the
53       * attribute is already there.
54       * @see #getAlreadyFilteredAttributeName
55       * @see #shouldNotFilter
56       * @see #doFilterInternal
57       */
58      public final void doFilter(ServletRequest   request, ServletResponse   response, FilterChain   filterChain)
59              throws ServletException  , IOException   {
60  
61          if (!(request instanceof HttpServletRequest  ) || !(response instanceof HttpServletResponse  )) {
62              throw new ServletException  ("OncePerRequestFilter just supports HTTP requests");
63          }
64          HttpServletRequest   httpRequest = (HttpServletRequest  ) request;
65          HttpServletResponse   httpResponse = (HttpServletResponse  ) response;
66  
67          String   alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
68          if (request.getAttribute(alreadyFilteredAttributeName) != null || shouldNotFilter(httpRequest)) {
69              // Proceed without invoking this filter...
70              filterChain.doFilter(request, response);
71          }
72          else {
73              // Do invoke this filter...
74              request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);
75              doFilterInternal(httpRequest, httpResponse, filterChain);
76          }
77      }
78  
79      /**
80       * Return the name of the request attribute that identifies that a request
81       * is already filtered.
82       * <p>Default implementation takes the configured name of the concrete filter
83       * instance and appends ".FILTERED". If the filter is not fully initialized,
84       * it falls back to its class name.
85       * @see #getFilterName
86       * @see #ALREADY_FILTERED_SUFFIX
87       */
88      protected String   getAlreadyFilteredAttributeName() {
89          String   name = getFilterName();
90          if (name == null) {
91              name = getClass().getName();
92          }
93          return name + ALREADY_FILTERED_SUFFIX;
94      }
95  
96      /**
97       * Can be overridden in subclasses for custom filtering control,
98       * returning <code>true</code> to avoid filtering of the given request.
99       * <p>The default implementation always returns <code>false</code>.
100      * @param request current HTTP request
101      * @return whether the given request should <i>not</i> be filtered
102      * @throws ServletException in case of errors
103      */
104     protected boolean shouldNotFilter(HttpServletRequest   request) throws ServletException   {
105         return false;
106     }
107 
108 
109     /**
110      * Same contract as for <code>doFilter</code>, but guaranteed to be
111      * just invoked once per request. Provides HttpServletRequest and
112      * HttpServletResponse arguments instead of the default ServletRequest
113      * and ServletResponse ones.
114      */
115     protected abstract void doFilterInternal(
116             HttpServletRequest   request, HttpServletResponse   response, FilterChain   filterChain)
117             throws ServletException  , IOException  ;
118 
119 }
120
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Popular Tags