！！请教此错误，Filter配置问题！！

package myFilter;

import java.io.*;
import javax.servlet.*;

public class SetCharEncodingFilter implements Filter
{
String encoding=null;
FilterConfig filterconfig=null;
boolean ignore=true;
public void destroy()
{this.encoding=null;
this.filterconfig=null;
}
public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain)throws IOException,ServletException
{
if(ignore||(request.getCharacterEncoding()==null))
{String encoding=selectEncoding(request);
if(encoding!=null)
{request.setCharacterEncoding(encoding);}
}
chain.doFilter(request,response);
}
public void init(FilterConfig filterConfig)throws ServletException
{
this.filterconfig=filterConfig;
this.encoding=filterConfig.getInitParameter("encoding");
String value=filterConfig.getInitParameter("ignore");
if((value==null)||(value.equalsIgnoreCase("true"))||(value.equalsIgnoreCase("yes")))
this.ignore=true;
else
this.ignore=false;
}
protected String selectEncoding(ServletRequest request)
{return (this.encoding);
}
}
编译没有问题的，多谢指教！