Spring CharacterEncodingFilter

 <!-- 配置请求过滤器，编码格式设为UTF-8，避免中文乱码-->
     <filter>
        <filter-name>springUtf8Encoding</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>springUtf8Encoding</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

注解配置：

@Bean
CharacterEncodingFilter characterEncodingFilter(){
	CharacterEncodingFilter filter = new CharacterEncodingFilter();
	filter.setEncoding("UTF-8");
	filter.setForceEncoding(true);
	return filter;
}

spring源码

 public class CharacterEncodingFilterextends OncePerRequestFilter {

     private String encoding;

     private boolean forceEncoding = false;

     /**
      * Set the encoding to usefor requests. This encoding will be passed into a
      * {@link javax.servlet.http.HttpServletRequest#setCharacterEncoding} call.
      * <p>Whether this encoding will overrideexisting request encodings
      * (and whether it will beapplied as default response encoding as well)
      * depends on the {@link #setForceEncoding "forceEncoding"} flag.
      */
     public void setEncoding(String encoding) {
        this.encoding = encoding;
     }

     /**
      * Set whether theconfigured {@link #setEncoding encoding} of this filter
      * is supposed to overrideexisting request and response encodings.
      * <p>Default is "false", i.e. do notmodify 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 onlybe set on Servlet 2.4+
      * containers, sinceServlet 2.3 did not provide a facility for setting
      * a default responseencoding.
      */
     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);
     }
 }

该字符集过滤器有两个重要参数，分别是encoding和forceEncoding

setEncoding

public void setEncoding(java.lang.String encoding)

Set the encodingto use for requests. This encoding will be passed into aServletRequest.setCharacterEncoding(java.lang.String) call.

setForceEncoding

public void setForceEncoding(boolean forceEncoding)

Set whether theconfigured encoding of this filter is supposed to override existing request andresponse encodings.

通过参考文档，我们可以知道：

l.第一个方法setEncoding()相当于：ServletRequest.setCharacterEncoding(java.lang.String)，即设置request编码格式。

2.第二个方法setForceEncoding()的作用是：同时设置ServletResponse和ServletRequest的编码格式。

配置相当于代码中：

resp.setCharacterEncoding("UTF-8");
req.setCharacterEncoding("UTF-8");

在请求处理的过程中我们可以不用考虑编码方面的问题，上面两句代码可以省略，编码统一交给Spring过滤器去处理。