SetCharacterEncodingFilter


1   /*
2    * $Header: /cvsroot/jgossipforum/release_01_01/src/org/jresearch/gossip/filters/SetCharacterEncodingFilter.java,v 1.3 2005/06/07 12:32:26 bel70 Exp $
3    * $Revision: 1.3 $
4    * $Date: 2005/06/07 12:32:26 $
5    *
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63  
64  package org.jresearch.gossip.filters;
65  
66  import java.io.IOException  ;
67  import java.util.Locale  ;
68  
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.http.HttpServletRequest  ;
76  import javax.servlet.http.HttpSession  ;
77  import javax.servlet.jsp.jstl.core.Config;
78  
79  import org.apache.struts.Globals;
80  
81  /**
82   * <p>
83   * Example filter that sets the character encoding to be used in parsing the
84   * incoming request, either unconditionally or only if the client did not
85   * specify a character encoding. Configuration of this filter is based on the
86   * following initialization parameters:
87   * </p>
88   * <ul>
89   * <li><strong>encoding</strong> - The character encoding to be configured for
90   * this request, either conditionally or unconditionally based on the
91   * <code>ignore</code> initialization parameter. This parameter is required,
92   * so there is no default.</li>
93   * <li><strong>ignore</strong> - If set to "true", any character encoding
94   * specified by the client is ignored, and the value returned by the
95   * <code>selectEncoding()</code> method is set. If set to "false,
96   * <code>selectEncoding()</code> is called <strong>only</strong> if the
97   * client has not already specified an encoding. By default, this parameter is
98   * set to "true".</li>
99   * </ul>
100  * 
101  * <p>
102  * Although this filter can be used unchanged, it is also easy to subclass it
103  * and make the <code>selectEncoding()</code> method more intelligent about
104  * what encoding to choose, based on characteristics of the incoming request
105  * (such as the values of the <code>Accept-Language</code> and
106  * <code>User-Agent</code> headers, or a value stashed in the current user's
107  * session.
108  * </p>
109  * 
110  * @author Craig McClanahan
111  * @version $Revision: 1.3 $ $Date: 2005/06/07 12:32:26 $
112  */
113 
114 public class SetCharacterEncodingFilter implements Filter   {
115 
116     // ----------------------------------------------------- Instance Variables
117 
118     /**
119      * The default character encoding to set for requests that pass through this
120      * filter.
121      */
122     protected String   encoding = null;
123 
124     /**
125      * The filter configuration object we are associated with. If this value is
126      * null, this filter instance is not currently configured.
127      */
128     protected FilterConfig   filterConfig = null;
129 
130     /**
131      * Should a character encoding specified by the client be ignored?
132      */
133     protected boolean ignore = true;
134 
135     // --------------------------------------------------------- Public Methods
136 
137     /**
138      * Take this filter out of service.
139      */
140     public void destroy() {
141 
142         this.encoding = null;
143         this.filterConfig = null;
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
152      *            The servlet request we are processing
153      * @param result
154      *            The servlet response we are creating
155      * @param chain
156      *            The filter chain we are processing
157      * 
158      * @exception IOException
159      *                if an input/output error occurs
160      * @exception ServletException
161      *                if a servlet error occurs
162      */
163     public void doFilter(ServletRequest   request, ServletResponse   response,
164             FilterChain   chain) throws IOException  , ServletException   {
165         // Conditionally select and set the character encoding to be used
166         if (ignore || (request.getCharacterEncoding() == null)) {
167             String   encoding = selectEncoding(request);
168             if (encoding != null) {
169                 request.setCharacterEncoding(encoding);
170             }
171         }
172         // Syncronize JSTL and struts locale settings
173         HttpSession   session = ((HttpServletRequest  ) request).getSession(true);
174         Locale   locale = (Locale  ) session.getAttribute(Globals.LOCALE_KEY);
175         if (locale == null) {
176             locale = request.getLocale();
177         }
178         Config.set(session, Config.FMT_LOCALE, locale);
179         // Pass control on to the next filter
180         chain.doFilter(request, response);
181 
182     }
183 
184     /**
185      * Place this filter into service.
186      * 
187      * @param filterConfig
188      *            The filter configuration object
189      */
190     public void init(FilterConfig   filterConfig) throws ServletException   {
191 
192         this.filterConfig = filterConfig;
193         this.encoding = filterConfig.getInitParameter("encoding");
194         String   value = filterConfig.getInitParameter("ignore");
195         if (value == null)
196             this.ignore = true;
197         else if (value.equalsIgnoreCase("true"))
198             this.ignore = true;
199         else if (value.equalsIgnoreCase("yes"))
200             this.ignore = true;
201         else
202             this.ignore = false;
203 
204     }
205 
206     // ------------------------------------------------------ Protected Methods
207 
208     /**
209      * Select an appropriate character encoding to be used, based on the
210      * characteristics of the current request and/or filter initialization
211      * parameters. If no character encoding should be set, return
212      * <code>null</code>.
213      * <p>
214      * The default implementation unconditionally returns the value configured
215      * by the <strong>encoding</strong> initialization parameter for this
216      * filter.
217      * 
218      * @param request
219      *            The servlet request we are processing
220      */
221     protected String   selectEncoding(ServletRequest   request) {
222 
223         return (this.encoding);
224 
225     }
226 
227 }
228
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