servlet过滤器

servlet的过滤器解决了是否登录状态问题。

1.创建一个AccessFilter类，基础代码

package valid.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 AccessFilter implements Filter{
    public void destroy() {
        System.out.println("请求销毁");
    }
    @Override
    public void doFilter(ServletRequest res, ServletResponse rep,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) res;
        HttpServletResponse response = (HttpServletResponse) rep;
        
        String requestURI = request.getRequestURI();
        String path = request.getContextPath();
        //如果请求路径等于首页ctl
        if(requestURI.startsWith(path + "/servlet/valServlet")){
            chain.doFilter(res, rep);
        }
        else{
            //这个时候，就说明需要判断权限了
            Object user = request.getSession().getAttribute("login");
            if(null == user){
                response.sendRedirect("../index.jsp");
            }else{
                chain.doFilter(res, rep);
            }
        }
        //放行
    }
    public void init(FilterConfig arg0) throws ServletException {
        System.out.println("请求初始化");
    }

}

2.web.xml配置

<filter>
     <filter-name>acess</filter-name>
     <filter-class>valid.filter.AccessFilter</filter-class>
 </filter>
 <filter-mapping>
     <filter-name>acess</filter-name>
     <url-pattern>/servlet/*</url-pattern>
 </filter-mapping>

所有servlet请求，都会先经过AccessFilter，只要没有登录状态，都将会被拦截，并跳转到首页