JSP页面访问用户验证(2)

然后，在 LoginFilter.java（web.xml配置文件中的com.homer.LoginFilter）文件中， 进行过滤验证：
[java
public class LoginFilter implements Filter { 
    @Override 
    public void init(FilterConfig arg0) throws ServletException { 
    } 
 
    @Override 
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException { 
        HttpServletRequest request = (HttpServletRequest)arg0; 
        HttpServletResponse response = (HttpServletResponse)arg1; 
         
        HttpSession session = request.getSession(); 
        if(session.getAttribute("userinfo") == null) { 
            response.setCharacterEncoding("utf-8"); 
            PrintWriter out = response.getWriter(); 
            out.print("<script>alert('您还没有登录，请登录...'); window.location='userlogin.html' </script>"); 
            out.flush(); 
            out.close(); 
 
//          request.setAttribute("loginError", "您还没有登录，请登录..."); 
//          request.getRequestDispatcher("userlogin.html").forward(request, response); 
        } else { 
            arg2.doFilter(request, response); 
        } 
    } 
 
    @Override 
    public void destroy() { 
    } 
} 

用户登录验证
用户登录验证，有两种方式：JSP网页前端和Java（Serlvet）后台
1） JSP网页前端验证（login.jsp）
[html] 
<% 
    String USERNAME = "admin"; 
    String USERPWD = "123456"; 
     
    request.setCharacterEncoding("utf8"); 
 
    String userName = request.getParameter("username").trim();