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Java > Open Source Codes > org > apache > webapp > admin > filters > SetCharacterEncodingFilter


1 /*
2  * Copyright 1999-2001,2004 The Apache Software Foundation.
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
18 package org.apache.webapp.admin.filters;
19
20
21 import java.io.IOException JavaDoc;
22 import javax.servlet.Filter JavaDoc;
23 import javax.servlet.FilterChain JavaDoc;
24 import javax.servlet.FilterConfig JavaDoc;
25 import javax.servlet.ServletException JavaDoc;
26 import javax.servlet.ServletRequest JavaDoc;
27 import javax.servlet.ServletResponse JavaDoc;
28 import javax.servlet.UnavailableException JavaDoc;
29
30
31 /**
32  * <p>Example filter that sets the character encoding to be used in parsing the
33  * incoming request, either unconditionally or only if the client did not
34  * specify a character encoding. Configuration of this filter is based on
35  * the following initialization parameters:</p>
36  * <ul>
37  * <li><strong>encoding</strong> - The character encoding to be configured
38  * for this request, either conditionally or unconditionally based on
39  * the <code>ignore</code> initialization parameter. This parameter
40  * is required, so there is no default.</li>
41  * <li><strong>ignore</strong> - If set to "true", any character encoding
42  * specified by the client is ignored, and the value returned by the
43  * <code>selectEncoding()</code> method is set. If set to "false,
44  * <code>selectEncoding()</code> is called <strong>only</strong> if the
45  * client has not already specified an encoding. By default, this
46  * parameter is set to "true".</li>
47  * </ul>
48  *
49  * <p>Although this filter can be used unchanged, it is also easy to
50  * subclass it and make the <code>selectEncoding()</code> method more
51  * intelligent about what encoding to choose, based on characteristics of
52  * the incoming request (such as the values of the <code>Accept-Language</code>
53  * and <code>User-Agent</code> headers, or a value stashed in the current
54  * user's session.</p>
55  *
56  * @author Craig McClanahan
57  * @version $Revision: 1.3 $ $Date: 2004/07/23 14:02:17 $
58  */
59
60 public class SetCharacterEncodingFilter implements Filter JavaDoc {
61
62
63     // ----------------------------------------------------- Instance Variables
64
65
66     /**
67      * The default character encoding to set for requests that pass through
68      * this filter.
69      */
70     protected String JavaDoc encoding = null;
71
72
73     /**
74      * The filter configuration object we are associated with. If this value
75      * is null, this filter instance is not currently configured.
76      */
77     protected FilterConfig JavaDoc filterConfig = null;
78
79
80     /**
81      * Should a character encoding specified by the client be ignored?
82      */
83     protected boolean ignore = true;
84
85
86     // --------------------------------------------------------- Public Methods
87
88
89     /**
90      * Take this filter out of service.
91      */
92     public void destroy() {
93
94         this.encoding = null;
95         this.filterConfig = null;
96
97     }
98
99
100     /**
101      * Select and set (if specified) the character encoding to be used to
102      * interpret request parameters for this request.
103      *
104      * @param request The servlet request we are processing
105      * @param result The servlet response we are creating
106      * @param chain The filter chain we are processing
107      *
108      * @exception IOException if an input/output error occurs
109      * @exception ServletException if a servlet error occurs
110      */
111     public void doFilter(ServletRequest JavaDoc request, ServletResponse JavaDoc response,
112                          FilterChain JavaDoc chain)
113     throws IOException JavaDoc, ServletException JavaDoc {
114
115         // Conditionally select and set the character encoding to be used
116 if (ignore || (request.getCharacterEncoding() == null)) {
117             String JavaDoc encoding = selectEncoding(request);
118             if (encoding != null)
119                 request.setCharacterEncoding(encoding);
120         }
121
122     // Pass control on to the next filter
123 chain.doFilter(request, response);
124
125     }
126
127
128     /**
129      * Place this filter into service.
130      *
131      * @param filterConfig The filter configuration object
132      */
133     public void init(FilterConfig JavaDoc filterConfig) throws ServletException JavaDoc {
134
135     this.filterConfig = filterConfig;
136         this.encoding = filterConfig.getInitParameter("encoding");
137         String JavaDoc value = filterConfig.getInitParameter("ignore");
138         if (value == null)
139             this.ignore = true;
140         else if (value.equalsIgnoreCase("true"))
141             this.ignore = true;
142         else if (value.equalsIgnoreCase("yes"))
143             this.ignore = true;
144         else
145             this.ignore = false;
146
147     }
148
149
150     // ------------------------------------------------------ Protected Methods
151
152
153     /**
154      * Select an appropriate character encoding to be used, based on the
155      * characteristics of the current request and/or filter initialization
156      * parameters. If no character encoding should be set, return
157      * <code>null</code>.
158      * <p>
159      * The default implementation unconditionally returns the value configured
160      * by the <strong>encoding</strong> initialization parameter for this
161      * filter.
162      *
163      * @param request The servlet request we are processing
164      */
165     protected String JavaDoc selectEncoding(ServletRequest JavaDoc request) {
166
167         return (this.encoding);
168
169     }
170
171
172 }
173
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