登陆filter

1.什么是fiter

　　Filter就像一个一个哨卡，用户的请求需要经过Filter,并且可以有多个过滤器

2.登陆filter作用

　　防止盗链接（没登陆就可以访问后台）

3.LoginFilter.java

package com.zy.filter;

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.HttpServletResponse;

public class LoginFilter implements Filter{

    @Override
    public void destroy() {
    }
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
　　　　  //doFilter方法的第一个参数req,是ServletRequest 类型的，不支持setCharacterEncoding，
        //所以要先强制转换为HttpServletRequest
        HttpServletRequest request = (HttpServletRequest)req;
        HttpServletResponse response = (HttpServletResponse)res;
        String uri = request.getServletPath();
　　　　　//静态资源放行
        if(uri.endsWith(".css")||uri.endsWith(".js")||uri.endsWith(".png")){
            chain.doFilter(request, response);
            return;
        }
　　　　　//登陆url放行
        if(uri.endsWith("login.jsp")||uri.endsWith("login")){
            chain.doFilter(request, response);
            return;
        }
        String loginname = (String)request.getSession().getAttribute("loginname");
　　　　　//session没账号缓存，不放行
        if(loginname == null){
            response.sendRedirect("login");
            return;
        }else{
            chain.doFilter(request, response);
            return;
        }
    }
    @Override
    public void init(FilterConfig arg0) throws ServletException {
    }

}

4.web.xml配置

       <!-- 登陆过滤 -->
    <filter>
        <filter-name>LoginFilter</filter-name>
        <filter-class>com.zy.filter.LoginFilter</filter-class>
    </filter>
     
    <filter-mapping>
        <filter-name>LoginFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>