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：

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/*

* 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：

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：

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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

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request.setCharacterEncoding(“”);

response.setCharacterEncoding(“”);

当值为false时，相当于：

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request.setCharacterEncoding(“”);

默认值为false。

示例：

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<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：

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request.setCharacterEncoding("UTF-8");

response.setCharacterEncoding("UTF-8");