java中的过滤器

过滤器相当于一个特殊的java类

 
如何在xml中配置过滤器

  <filter>
    <filter-name>filter</filter-name>
    <filter-class>five.MyFilter</filter-class>
</filter>
<filter-mapping>
   <filter-name>filter</filter-name>
   <url-pattern>/show.jsp</url-pattern>
</filter-mapping>

 

如判断用户登录

  package five;

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.HttpSession;

public class MyFilter implements Filter{

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req=(HttpServletRequest)request;
        HttpSession session=req.getSession(); 
        String name=(String)session.getAttribute("name");  //得到servlet保存的session用户名
        if(name==null||"".equals(name)){
            request.getRequestDispatcher("index.jsp").forward(request, response);
        }
        chain.doFilter(request, response);//如果存在则执行jsp页面或servlet
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        
    }

}