一个过过滤器

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.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class ChinaFilter implements Filter
{
    String encoding="UTF-8";
    String []words;
    public void destroy()
    {
       encoding=null;
       words=null;
    }
   
    public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain filter)
        throws IOException, ServletException
    {
        System.out.println("开始过滤:"+encoding);
        request.setCharacterEncoding(encoding);
        Request req = new Request((HttpServletRequest)request);
        response.setCharacterEncoding(encoding);
        System.out.println("结束过滤:"+encoding);
        filter.doFilter(req, response);
       
    }
   
    public void init(FilterConfig filter)
        throws ServletException
    {
        String getEncoding = filter.getInitParameter("encoding");
       if(null!=getEncoding && "".equals(getEncoding))
       {
           this.encoding = getEncoding;
       }
       words = new String[]{"混蛋","笨蛋"};
    }
   
    private String Filter(String param)
    {
        if(null!=words && words.length>0)
        {
            for (int i = 0; i < words.length; i++)
            {
                param=param.replaceAll(words[i], "****");
            }
        }
        return param;       
    }
   
    class Request extends HttpServletRequestWrapper
    {
        protected Request(HttpServletRequest request)
        {
            super(request);
        }

        public String getParameter(String name)
        {
            String value=super.getParameter(name);
            if(null!=value)
            {
                return Filter(value);
            }
            return null;
        }

        public String[] getParameterValues(String name)
        {
            String[] values = super.getParameterValues(name);
            if(null!=values && values.length>0)
            {
                for (int i = 0; i < values.length; i++)
                {
                    values[i]=Filter(values[i]);
                }
                return values;
            }
            return null;
        }
       
       
    }
   
}
web.xml
<filter>
  <filter-name>filter</filter-name>
  <filter-class>filter.ChinaFilter</filter-class>
  <init-param>
  <param-name>encoding</param-name>
  <param-value>GBK</param-value>
  </init-param>
  </filter>
  <filter-mapping>
  <filter-name>filter</filter-name>
  <url-pattern>/*</url-pattern>
  </filter-mapping>