| SetCharacterEncodingFilter.java |
1 /*
2 * $Header: /home/cvs/jakarta-servletapi-5/jsr154/examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java,v 1.1 2002/09/02 13:14:53 remm Exp $
3 * $Revision: 1.1 $
4 * $Date: 2002/09/02 13:14:53 $
5 *
6 * ====================================================================
7 *
8 * The Apache Software License, Version 1.1
9 *
10 * Copyright (c) 1999-2001 The Apache Software Foundation. All rights
11 * reserved.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 *
17 * 1. Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 *
20 * 2. Redistributions in binary form must reproduce the above copyright
21 * notice, this list of conditions and the following disclaimer in
22 * the documentation and/or other materials provided with the
23 * distribution.
24 *
25 * 3. The end-user documentation included with the redistribution, if
26 * any, must include the following acknowlegement:
27 * "This product includes software developed by the
28 * Apache Software Foundation (http://www.apache.org/)."
29 * Alternately, this acknowlegement may appear in the software itself,
30 * if and wherever such third-party acknowlegements normally appear.
31 *
32 * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software
33 * Foundation" must not be used to endorse or promote products derived
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62 */
63
64
65package tw.com.javaworld.CH11;
66
67
68import java.io.IOException;
69import javax.servlet.Filter;
70import javax.servlet.FilterChain;
71import javax.servlet.FilterConfig;
72import javax.servlet.ServletException;
73import javax.servlet.ServletRequest;
74import javax.servlet.ServletResponse;
75import 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>
00 * and <code>User-Agent</code> headers, or a value stashed in the current
01 * user's session.</p>
02 *
03 * @author Craig McClanahan
04 * @version $Revision: 1.1 $ $Date: 2002/09/02 13:14:53 $
05 */
06
07public class SetCharacterEncodingFilter implements Filter {
08
09
10 // ----------------------------------------------------- Instance Variables
11
12
13 /**
14 * The default character encoding to set for requests that pass through
15 * this filter.
16 */
17 protected String encoding = null;
18
19
20 /**
21 * The filter configuration object we are associated with. If this value
22 * is null, this filter instance is not currently configured.
23 */
24 protected FilterConfig filterConfig = null;
25
26
27 /**
28 * Should a character encoding specified by the client be ignored?
29 */
30 protected boolean ignore = true;
31
32
33 // --------------------------------------------------------- Public Methods
34
35
36 /**
37 * Take this filter out of service.
38 */
39 public void destroy() {
40
41 this.encoding = null;
42 this.filterConfig = null;
43
44 }
45
46
47 /**
48 * Select and set (if specified) the character encoding to be used to
49 * interpret request parameters for this request.
50 *
51 * @param request The servlet request we are processing
52 * @param result The servlet response we are creating
53 * @param chain The filter chain we are processing
54 *
55 * @exception IOException if an input/output error occurs
56 * @exception ServletException if a servlet error occurs
57 */
58 public void doFilter(ServletRequest request, ServletResponse response,
59 FilterChain chain)
60 throws IOException, ServletException {
61
62 // Conditionally select and set the character encoding to be used
63 if (ignore || (request.getCharacterEncoding() == null)) {
64 String encoding = selectEncoding(request);
65 if (encoding != null)
66 request.setCharacterEncoding(encoding);
67 }
68
69 // Pass control on to the next filter
70 chain.doFilter(request, response);
71
72 }
73
74
75 /**
76 * Place this filter into service.
77 *
78 * @param filterConfig The filter configuration object
79 */
80 public void init(FilterConfig filterConfig) throws ServletException {
81
82 this.filterConfig = filterConfig;
83 this.encoding = filterConfig.getInitParameter("encoding");
84 String value = filterConfig.getInitParameter("ignore");
85 if (value == null)
86 this.ignore = true;
87 else if (value.equalsIgnoreCase("true"))
88 this.ignore = true;
89 else if (value.equalsIgnoreCase("yes"))
90 this.ignore = true;
91 else
92 this.ignore = false;
93
94 }
95
96
97 // ------------------------------------------------------ Protected Methods
98
99
00 /**
01 * Select an appropriate character encoding to be used, based on the
02 * characteristics of the current request and/or filter initialization
03 * parameters. If no character encoding should be set, return
04 * <code>null</code>.
05 * <p>
06 * The default implementation unconditionally returns the value configured
07 * by the <strong>encoding</strong> initialization parameter for this
08 * filter.
09 *
10 * @param request The servlet request we are processing
11 */
12 protected String selectEncoding(ServletRequest request) {
13
14 return (this.encoding);
15
16 }
17
18
19}
20