Spring mvc中内置编码过滤器的原理是什么

<filter>  <filter-name>characterEncodingFilter</filter-name>  <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>  <!-- 字符编码 --> <init-param>  <param-name>encoding</param-name>  <param-value>UTF-8</param-value>  </init-param>  <!-- 是否强制所有请求都使用该字符编码 --> <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>