tomcat中的一个过滤器例子

感谢：http://www.iteye.com/wiki/Struts/578-Struts原理与实践（5） 和Google

将所有的request的字符集也设置为UTF-8。虽然，我们可以在每个文件中加入这样的句子：request.setCharacterEncoding("UTF-8");来解决，但这样显得很麻烦。一种更简单的解决方法是使用filter。具体步骤如下： 

在mystruts\WEB-INF\classes目录下再新建一个名为filters的目录，新建一个名为：SetCharacterEncodingFilter的类，并保存在该目录下。其实，这个类并不要您亲自来写，可以借用tomcat中的例子。现将该例子的程序节选如下： 

package filters;
 import java.io.IOException;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 import javax.servlet.UnavailableException;

 public class SetCharacterEncodingFilter implements Filter {


  //可以理解为默认编码，在web.xml中配置后读取存入
     protected String encoding = null;


     protected FilterConfig filterConfig = null;

     protected boolean ignore = true;

     public void destroy() {

         this.encoding = null;
         this.filterConfig = null;

    }


     public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain)
         throws IOException, ServletException {

         // Conditionally select and set the character encoding to be used
 //如果被忽略或者请求未设置编码，为了防止乱码，进行编码过滤
         if (ignore || (request.getCharacterEncoding() == null)) {
 //设置请求编码为web.xml中配置的编码类型
            String encoding = selectEncoding(request);
             if (encoding != null)
                request.setCharacterEncoding(encoding);
        }

         // Pass control on to the next filter
 //由FilterChain进行过滤处理，而不是该Filter
        chain.doFilter(request, response);

    }

  //主要从配置文件中读取配置项并进行赋值
     public void init(FilterConfig filterConfig) throws ServletException {

         this.filterConfig = filterConfig;
   //从web.xml读取配置的编码，如gbk，utf－8等，赋值给encoding
         this.encoding = filterConfig.getInitParameter("encoding");
   //从web.xml读取是否忽略
        String value = filterConfig.getInitParameter("ignore");
        if (value == null)
            this.ignore = true;
        else if (value.equalsIgnoreCase("true"))
            this.ignore = true;
        else if (value.equalsIgnoreCase("yes"))
             this.ignore = true;
         else
             this.ignore = false;

    }
  protected String selectEncoding(ServletRequest request) {

         return (this.encoding);

    }

}
<filter>
     <filter-name>Set Character Encodingfilter-name>
     <filter-class>filters.SetCharacterEncodingFilterfilter-class>
     <init-param>
       <param-name>encodingparam-name>
       <param-value>UTF-8param-value>
     init-param>
   filter>
   <filter-mapping>
     <filter-name>Set Character Encodingfilter-name>
     <url-pattern>/*url-pattern>
 filter-mapping>