001 /*
002 * Copyright 2004 The Apache Software Foundation
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package filters;
018
019
020 import java.io.IOException;
021 import javax.servlet.Filter;
022 import javax.servlet.FilterChain;
023 import javax.servlet.FilterConfig;
024 import javax.servlet.ServletException;
025 import javax.servlet.ServletRequest;
026 import javax.servlet.ServletResponse;
027 import javax.servlet.UnavailableException;
028
029
030 /**
031 * <p>Example filter that sets the character encoding to be used in parsing the
032 * incoming request, either unconditionally or only if the client did not
033 * specify a character encoding. Configuration of this filter is based on
034 * the following initialization parameters:</p>
035 * <ul>
036 * <li><strong>encoding</strong> - The character encoding to be configured
037 * for this request, either conditionally or unconditionally based on
038 * the <code>ignore</code> initialization parameter. This parameter
039 * is required, so there is no default.</li>
040 * <li><strong>ignore</strong> - If set to "true", any character encoding
041 * specified by the client is ignored, and the value returned by the
042 * <code>selectEncoding()</code> method is set. If set to "false,
043 * <code>selectEncoding()</code> is called <strong>only</strong> if the
044 * client has not already specified an encoding. By default, this
045 * parameter is set to "true".</li>
046 * </ul>
047 *
048 * <p>Although this filter can be used unchanged, it is also easy to
049 * subclass it and make the <code>selectEncoding()</code> method more
050 * intelligent about what encoding to choose, based on characteristics of
051 * the incoming request (such as the values of the <code>Accept-Language</code>
052 * and <code>User-Agent</code> headers, or a value stashed in the current
053 * user's session.</p>
054 *
055 * @author Craig McClanahan
056 * @version $Revision: 267129 $ $Date: 2004-03-18 08:40:35 -0800 (Thu, 18 Mar 2004) $
057 */
058
059 public class SetCharacterEncodingFilter implements Filter {
060
061
062 // ----------------------------------------------------- Instance Variables
063
064
065 /**
066 * The default character encoding to set for requests that pass through
067 * this filter.
068 */
069 protected String encoding = null;
070
071
072 /**
073 * The filter configuration object we are associated with. If this value
074 * is null, this filter instance is not currently configured.
075 */
076 protected FilterConfig filterConfig = null;
077
078
079 /**
080 * Should a character encoding specified by the client be ignored?
081 */
082 protected boolean ignore = true;
083
084
085 // --------------------------------------------------------- Public Methods
086
087
088 /**
089 * Take this filter out of service.
090 */
091 public void destroy() {
092
093 this.encoding = null;
094 this.filterConfig = null;
095
096 }
097
098
099 /**
100 * Select and set (if specified) the character encoding to be used to
101 * interpret request parameters for this request.
102 *
103 * @param request The servlet request we are processing
104 * @param result The servlet response we are creating
105 * @param chain The filter chain we are processing
106 *
107 * @exception IOException if an input/output error occurs
108 * @exception ServletException if a servlet error occurs
109 */
110 public void doFilter(ServletRequest request, ServletResponse response,
111 FilterChain chain)
112 throws IOException, ServletException {
113
114 // Conditionally select and set the character encoding to be used
115 if (ignore || (request.getCharacterEncoding() == null)) {
116 String encoding = selectEncoding(request);
117 if (encoding != null)
118 request.setCharacterEncoding(encoding);
119 }
120
121 // Pass control on to the next filter
122 chain.doFilter(request, response);
123
124 }
125
126
127 /**
128 * Place this filter into service.
129 *
130 * @param filterConfig The filter configuration object
131 */
132 public void init(FilterConfig filterConfig) throws ServletException {
133
134 this.filterConfig = filterConfig;
135 this.encoding = filterConfig.getInitParameter("encoding");
136 String value = filterConfig.getInitParameter("ignore");
137 if (value == null)
138 this.ignore = true;
139 else if (value.equalsIgnoreCase("true"))
140 this.ignore = true;
141 else if (value.equalsIgnoreCase("yes"))
142 this.ignore = true;
143 else
144 this.ignore = false;
145
146 }
147
148
149 // ------------------------------------------------------ Protected Methods
150
151
152 /**
153 * Select an appropriate character encoding to be used, based on the
154 * characteristics of the current request and/or filter initialization
155 * parameters. If no character encoding should be set, return
156 * <code>null</code>.
157 * <p>
158 * The default implementation unconditionally returns the value configured
159 * by the <strong>encoding</strong> initialization parameter for this
160 * filter.
161 *
162 * @param request The servlet request we are processing
163 */
164 protected String selectEncoding(ServletRequest request) {
165
166 return (this.encoding);
167
168 }
169
170
171 }