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
018 package filters;
019
020
021 import java.io.IOException;
022 import javax.servlet.Filter;
023 import javax.servlet.FilterChain;
024 import javax.servlet.FilterConfig;
025 import javax.servlet.ServletContext;
026 import javax.servlet.ServletException;
027 import javax.servlet.ServletRequest;
028 import javax.servlet.ServletResponse;
029
030
031 /**
032 * Example filter that can be attached to either an individual servlet
033 * or to a URL pattern. This filter performs the following functions:
034 * <ul>
035 * <li>Attaches itself as a request attribute, under the attribute name
036 * defined by the value of the <code>attribute</code> initialization
037 * parameter.</li>
038 * <li>Calculates the number of milliseconds required to perform the
039 * servlet processing required by this request, including any
040 * subsequently defined filters, and logs the result to the servlet
041 * context log for this application.
042 * </ul>
043 *
044 * @author Craig McClanahan
045 * @version $Revision: 267129 $ $Date: 2004-03-18 08:40:35 -0800 (Thu, 18 Mar 2004) $
046 */
047
048 public final class ExampleFilter implements Filter {
049
050
051 // ----------------------------------------------------- Instance Variables
052
053
054 /**
055 * The request attribute name under which we store a reference to ourself.
056 */
057 private String attribute = null;
058
059
060 /**
061 * The filter configuration object we are associated with. If this value
062 * is null, this filter instance is not currently configured.
063 */
064 private FilterConfig filterConfig = null;
065
066
067 // --------------------------------------------------------- Public Methods
068
069
070 /**
071 * Take this filter out of service.
072 */
073 public void destroy() {
074
075 this.attribute = null;
076 this.filterConfig = null;
077
078 }
079
080
081 /**
082 * Time the processing that is performed by all subsequent filters in the
083 * current filter stack, including the ultimately invoked servlet.
084 *
085 * @param request The servlet request we are processing
086 * @param result The servlet response we are creating
087 * @param chain The filter chain we are processing
088 *
089 * @exception IOException if an input/output error occurs
090 * @exception ServletException if a servlet error occurs
091 */
092 public void doFilter(ServletRequest request, ServletResponse response,
093 FilterChain chain)
094 throws IOException, ServletException {
095
096 // Store ourselves as a request attribute (if requested)
097 if (attribute != null)
098 request.setAttribute(attribute, this);
099
100 // Time and log the subsequent processing
101 long startTime = System.currentTimeMillis();
102 chain.doFilter(request, response);
103 long stopTime = System.currentTimeMillis();
104 filterConfig.getServletContext().log
105 (this.toString() + ": " + (stopTime - startTime) +
106 " milliseconds");
107
108 }
109
110
111 /**
112 * Place this filter into service.
113 *
114 * @param filterConfig The filter configuration object
115 */
116 public void init(FilterConfig filterConfig) throws ServletException {
117
118 this.filterConfig = filterConfig;
119 this.attribute = filterConfig.getInitParameter("attribute");
120
121 }
122
123
124 /**
125 * Return a String representation of this object.
126 */
127 public String toString() {
128
129 if (filterConfig == null)
130 return ("InvokerFilter()");
131 StringBuffer sb = new StringBuffer("InvokerFilter(");
132 sb.append(filterConfig);
133 sb.append(")");
134 return (sb.toString());
135
136 }
137
138
139 }
140