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;
}
@Override
protected 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：
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
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");
