Spring MVC过滤器-字符集过滤器（CharacterEncodingFilter）

Spring的字符集过滤通过用于处理项目中的乱码问题，该过滤器位于org.springframework.web.filter包中，指向类CharacterEncodingFilter，CharacterEncodingFilter源代码如下：

/* * Copyright 2002-2007 the original author or authors. * * 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 org.springframework.web.filter;import java.io.IOException;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet 2.3/2.4 Filter that allows one to specify a character encoding for * requests. This is useful because current browsers typically do not set a * character encoding even if specified in the HTML page or form. * * <p>This filter can either apply its encoding if the request does not * already specify an encoding, or enforce this filter's encoding in any case * ("forceEncoding"="true"). In the latter case, the encoding will also be * applied as default response encoding on Servlet 2.4+ containers (although * this will usually be overridden by a full content type set in the view). * * @author Juergen Hoeller * @since 15.03.2004 * @see #setEncoding * @see #setForceEncoding * @see javax.servlet.http.HttpServletRequest#setCharacterEncoding * @see javax.servlet.http.HttpServletResponse#setCharacterEncoding */public class CharacterEncodingFilter extends OncePerRequestFilter {private String encoding;private boolean forceEncoding = false;/** * Set the encoding to use for requests. This encoding will be passed into a * {@link javax.servlet.http.HttpServletRequest#setCharacterEncoding} call. * <p>Whether this encoding will override existing request encodings * (and whether it will be applied as default response encoding as well) * depends on the {@link #setForceEncoding "forceEncoding"} flag. */public void setEncoding(String encoding) {this.encoding = encoding;}/** * Set whether the configured {@link #setEncoding encoding} of this filter * is supposed to override existing request and response encodings. * <p>Default is "false", i.e. do not modify the encoding if * {@link javax.servlet.http.HttpServletRequest#getCharacterEncoding()} * returns a non-null value. Switch this to "true" to enforce the specified * encoding in any case, applying it as default response encoding as well. * <p>Note that the response encoding will only be set on Servlet 2.4+ * containers, since Servlet 2.3 did not provide a facility for setting * a default response encoding. */public void setForceEncoding(boolean forceEncoding) {this.forceEncoding = forceEncoding;}@Overrideprotected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)throws ServletException, IOException {if (this.encoding != null && (this.forceEncoding || request.getCharacterEncoding() == null)) {request.setCharacterEncoding(this.encoding);if (this.forceEncoding) {response.setCharacterEncoding(this.encoding);}}filterChain.doFilter(request, response);}}

        上述代码显示，在配置字符集过滤器时可设定两个参数的值，如下：

        l  encoding：字符集，即将过滤到的request的字符集设置为encoding指定的值，如UTF-8等，相当于：

request.setCharacterEncoding

        l  forceEncoding：字面意思是强制字符集，但你大可不必按字面意思理解，因为这个参数的值只不过是指定response的字符集是否也设置成encoding所指定的字符集，所以你可以选择设置为true或false，当值为true时，相当于

request.setCharacterEncoding(“”);response.setCharacterEncoding(“”);

        当值为false时，相当于：

request.setCharacterEncoding(“”);

        默认值为false。

        示例：

        <filter><filter-name>characterEncodingFilter</filter-name><filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class><init-param><param-name>encoding</param-name><param-value>UTF-8</param-value></init-param><init-param><param-name>forceEncoding</param-name><param-value>true</param-value></init-param></filter><filter-mapping><filter-name>characterEncodingFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>

        以上代码放置在web.xml中，相当于servlet中的：

request.setCharacterEncoding("UTF-8");response.setCharacterEncoding("UTF-8");