SetCharacterEncodingFilter


1   /*
2    * $Header: /home/cvs/jakarta-tomcat-4.0/webapps/examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java,v 1.2 2001/10/17 22:53:19 craigmcc Exp $
3    * $Revision: 1.2 $
4    * $Date: 2001/10/17 22:53:19 $
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63  
64  
65  package filters;
66  
67  
68  import java.io.IOException  ;
69  import javax.servlet.Filter  ;
70  import javax.servlet.FilterChain  ;
71  import javax.servlet.FilterConfig  ;
72  import javax.servlet.ServletException  ;
73  import javax.servlet.ServletRequest  ;
74  import javax.servlet.ServletResponse  ;
75  import javax.servlet.UnavailableException  ;
76  
77  
78  /**
79   * <p>Example filter that sets the character encoding to be used in parsing the
80   * incoming request, either unconditionally or only if the client did not
81   * specify a character encoding.  Configuration of this filter is based on
82   * the following initialization parameters:</p>
83   * <ul>
84   * <li><strong>encoding</strong> - The character encoding to be configured
85   *     for this request, either conditionally or unconditionally based on
86   *     the <code>ignore</code> initialization parameter.  This parameter
87   *     is required, so there is no default.</li>
88   * <li><strong>ignore</strong> - If set to "true", any character encoding
89   *     specified by the client is ignored, and the value returned by the
90   *     <code>selectEncoding()</code> method is set.  If set to "false,
91   *     <code>selectEncoding()</code> is called <strong>only</strong> if the
92   *     client has not already specified an encoding.  By default, this
93   *     parameter is set to "true".</li>
94   * </ul>
95   *
96   * <p>Although this filter can be used unchanged, it is also easy to
97   * subclass it and make the <code>selectEncoding()</code> method more
98   * intelligent about what encoding to choose, based on characteristics of
99   * the incoming request (such as the values of the <code>Accept-Language</code>
100  * and <code>User-Agent</code> headers, or a value stashed in the current
101  * user's session.</p>
102  *
103  * @author Craig McClanahan
104  * @version $Revision: 1.2 $ $Date: 2001/10/17 22:53:19 $
105  */
106 
107 public class SetCharacterEncodingFilter implements Filter   {
108 
109 
110     // ----------------------------------------------------- Instance Variables
111 
112 
113     /**
114      * The default character encoding to set for requests that pass through
115      * this filter.
116      */
117     protected String   encoding = null;
118 
119 
120     /**
121      * The filter configuration object we are associated with.  If this value
122      * is null, this filter instance is not currently configured.
123      */
124     protected FilterConfig   filterConfig = null;
125 
126 
127     /**
128      * Should a character encoding specified by the client be ignored?
129      */
130     protected boolean ignore = true;
131 
132 
133     // --------------------------------------------------------- Public Methods
134 
135 
136     /**
137      * Take this filter out of service.
138      */
139     public void destroy() {
140 
141         this.encoding = null;
142         this.filterConfig = null;
143 
144     }
145 
146 
147     /**
148      * Select and set (if specified) the character encoding to be used to
149      * interpret request parameters for this request.
150      *
151      * @param request The servlet request we are processing
152      * @param result The servlet response we are creating
153      * @param chain The filter chain we are processing
154      *
155      * @exception IOException if an input/output error occurs
156      * @exception ServletException if a servlet error occurs
157      */
158     public void doFilter(ServletRequest   request, ServletResponse   response,
159                          FilterChain   chain)
160     throws IOException  , ServletException   {
161 
162         // Conditionally select and set the character encoding to be used
163         if (ignore || (request.getCharacterEncoding() == null)) {
164             String   encoding = selectEncoding(request);
165             if (encoding != null)
166                 request.setCharacterEncoding(encoding);
167         }
168 
169     // Pass control on to the next filter
170         chain.doFilter(request, response);
171 
172     }
173 
174 
175     /**
176      * Place this filter into service.
177      *
178      * @param filterConfig The filter configuration object
179      */
180     public void init(FilterConfig   filterConfig) throws ServletException   {
181 
182     this.filterConfig = filterConfig;
183         this.encoding = filterConfig.getInitParameter("encoding");
184         String   value = filterConfig.getInitParameter("ignore");
185         if (value == null)
186             this.ignore = true;
187         else if (value.equalsIgnoreCase("true"))
188             this.ignore = true;
189         else if (value.equalsIgnoreCase("yes"))
190             this.ignore = true;
191         else
192             this.ignore = false;
193 
194     }
195 
196 
197     // ------------------------------------------------------ Protected Methods
198 
199 
200     /**
201      * Select an appropriate character encoding to be used, based on the
202      * characteristics of the current request and/or filter initialization
203      * parameters.  If no character encoding should be set, return
204      * <code>null</code>.
205      * <p>
206      * The default implementation unconditionally returns the value configured
207      * by the <strong>encoding</strong> initialization parameter for this
208      * filter.
209      *
210      * @param request The servlet request we are processing
211      */
212     protected String   selectEncoding(ServletRequest   request) {
213 
214         return (this.encoding);
215 
216     }
217 
218 
219 }
220
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