java Filter的实际应用一例用户登录

package com.tongtech.bjvsp.sysmng.filter;   
  
import java.io.IOException;   
import java.io.PrintWriter;   
  
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.HttpServlet;   
import javax.servlet.http.HttpServletRequest;   
import javax.servlet.http.HttpServletResponse;   
  
import com.tongtech.bjvsp.sysmng.constant.ConstantServlet;   
  
public class EncodingFilter extends HttpServlet implements Filter {   
    private FilterConfig filterConfig;   
  
    // Handle the passed-in FilterConfig   
    public void init(FilterConfig filterConfig) throws ServletException {   
        this.filterConfig = filterConfig;   
    }   
  
    // Process the request/response pair   
    public void doFilter(ServletRequest request, ServletResponse response,   
            FilterChain filterChain) {   
        try {   
  
            HttpServletRequest httpRequest = (HttpServletRequest) request;   
            HttpServletResponse httpResponse = (HttpServletResponse) response;   
            boolean isValid = true;   
            String uriStr = httpRequest.getRequestURI();   
            if (uriStr.indexOf(".jsp") == -1 && uriStr.indexOf(".do") == -1) {   
                isValid = true;   
            } else if (uriStr.indexOf("login.jsp") == -1 && uriStr.indexOf("login.do") == -1  
                    && httpRequest.getSession().getAttribute("UserWraper") == null) {   
                isValid = false;   
            }   
  
            if (isValid) {   
                request.setCharacterEncoding("GBK");   
                filterChain.doFilter(request, response);   
            }   
  
            else {   
                request.setCharacterEncoding("GBK");   
                PrintWriter out = httpResponse.getWriter();   
                if( uriStr.indexOf("index.jsp") == -1 ) {   
                    out.write("<script>window.parent.parent.location.href='../../login.jsp'</script>");   
                } else {   
                    out.write("<script>window.parent.parent.location.href='../login.jsp'</script>");   
                }   
  
            }   
  
        } catch (ServletException sx) {   
            filterConfig.getServletContext().log(sx.getMessage());   
        } catch (IOException iox) {   
            filterConfig.getServletContext().log(iox.getMessage());   
        }   
    }   
  
    // Clean up resources   
    public void destroy() {   
    }   
}  

<filter>   
    <filter-name>encodingfilter</filter-name>   
    <filter-class>com.tongtech.bjvsp.sysmng.filter.EncodingFilter</filter-class>   
  </filter>   
  <filter-mapping>   
    <filter-name>encodingfilter</filter-name>   
    <url-pattern>/*</url-pattern>   
  </filter-mapping>