Tomcat环境下，字符编码的filter

【原文地址】 http://www.blogjava.net/yczz/articles/106473.html

在web.xml中，配置"Set Character Encoding" filter，可以实现客户端传入服务器端的Request对象中的数据的正确解码。

我使用的filter是Craig McClanahan写的，这位仁兄大名鼎鼎，他是Struts框架的主要体系设计师和开发者，Tomcat4的主设计师和Java Web Services Developer Pack实现包的主设计师，领导着Sun的JavaServer Faces规范开发，同时也是Java EE平台的Web Layer Archiecture。filter的代码附在文后。

web.xml中的配置如下：

<!-- GBK Encodinbg Filter definition --><filter><filter-name>Set Character Encoding</filter-name><filter-class>filters.SetCharacterEncodingFilter</filter-class><init-param><param-name>encoding</param-name><param-value>GBK</param-value></init-param></filter><!-- GBK Encoding Filter mapping --><filter-mapping><filter-name>Set Character Encoding</filter-name><url-pattern>/*</url-pattern></filter-mapping>

/** Copyright 2004 The Apache Software Foundation** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at** http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES or CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/package filters;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;/*** <p>Example filter that sets the character encoding to be used in parsing the* incoming request, either unconditionally or only if the client did not* specify a character encoding. Configuration of this filter is based on* the following initialization parameters:</p>* <ul>* <li><strong>encoding</strong> - The character encoding to be configured* for this request, either conditionally or unconditionally based on* the <code>ignore</code> initialization parameter. This parameter* is required, so there is no default.</li>* <li><strong>ignore</strong> - If set to "true", any character encoding* specified by the client is ignored, and the value returned by the* <code>selectEncoding()</code> method is set. If set to "false,* <code>selectEncoding()</code> is called <strong>only</strong> if the* client has not already specified an encoding. By default, this* parameter is set to "true".</li>* </ul>** <p>Although this filter can be used unchanged, it is also easy to* subclass it and make the <code>selectEncoding()</code> method more* intelligent about what encoding to choose, based on characteristics of* the incoming request (such as the values of the <code>Accept-Language</code>* and <code>User-Agent</code> headers, or a value stashed in the current* user's session.</p>** @author Craig McClanahan* @version $Revision: 1.2 $ $Date: 2004/03/18 16:40:33 $*/public class SetCharacterEncodingFilter implements Filter {// ----------------------------------------------------- Instance Variables/*** The default character encoding to set for requests that pass through* this filter.*/protected String encoding = null;/*** The filter configuration object we are associated with. If this value* is null, this filter instance is not currently configured.*/protected FilterConfig filterConfig = null;/*** Should a character encoding specified by the client be ignored?*/protected boolean ignore = true;// --------------------------------------------------------- Public Methods/*** Take this filter out of service.*/public void destroy() {this.encoding = null;this.filterConfig = null;}/*** Select and set (if specified) the character encoding to be used to* interpret request parameters for this request.** @param request The servlet request we are processing* @param result The servlet response we are creating* @param chain The filter chain we are processing** @exception IOException if an input/output error occurs* @exception ServletException if a servlet error occurs*/public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain)throws IOException, ServletException {// Conditionally select and set the character encoding to be usedif (ignore || (request.getCharacterEncoding() == null)) {String encoding = selectEncoding(request);if (encoding != null)request.setCharacterEncoding(encoding);}// Pass control on to the next filterchain.doFilter(request, response);}/*** Place this filter into service.** @param filterConfig The filter configuration object*/public void init(FilterConfig filterConfig) throws ServletException {this.filterConfig = filterConfig;this.encoding = filterConfig.getInitParameter("encoding");String value = filterConfig.getInitParameter("ignore");if (value == null)this.ignore = true;else if (value.equalsIgnoreCase("true"))this.ignore = true;else if (value.equalsIgnoreCase("yes"))this.ignore = true;elsethis.ignore = false;}// ------------------------------------------------------ Protected Methods/*** Select an appropriate character encoding to be used, based on the* characteristics of the current request and/or filter initialization* parameters. If no character encoding should be set, return* <code>null</code>.* <p>* The default implementation unconditionally returns the value configured* by the <strong>encoding</strong> initialization parameter for this* filter.** @param request The servlet request we are processing*/protected String selectEncoding(ServletRequest request) {return (this.encoding);}}