通过原理解析Spring mvc的内置编码过滤器

<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> 

public class CharacterEncodingFilter extends OncePerRequestFilter {

 private String encoding;
 private boolean forceRequestEncoding = false;
 private boolean forceResponseEncoding = false;

 public void setEncoding(String encoding) {
 this.encoding = encoding;
 }

 public void setForceEncoding(boolean forceEncoding) {
 this.forceRequestEncoding = forceEncoding;
 this.forceResponseEncoding = forceEncoding;
 }

 @Override
 protected void doFilterInternal(
  HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
  throws ServletException, IOException {

 String encoding = getEncoding();
 if (encoding != null) {
  if (isForceRequestEncoding() || request.getCharacterEncoding() == null) {
  request.setCharacterEncoding(encoding);
  }
  if (isForceResponseEncoding()) {
  response.setCharacterEncoding(encoding);
  }
 }
 filterChain.doFilter(request, response);
 }
 ......
}