简单filter权限控制

download。jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>download</title>
</head>
<body>
<a href="">ziyau1</a>
<a href="">ziya2</a>
<a href="">ziyau3</a>
</body>
</html>
login.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>login</title>
</head>
<body>
<form action="/login"method="post">
    <input type="text"name="name"><br>
    <input type="password"name="password"><br>

    <input type="submit"value="提交">

</form>

</body>
</html>
loginservlet

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String name=req.getParameter("name");
        String password=req.getParameter("password");
        if(name.equals("admin")&&password.equals("123")){
            HttpSession session=req.getSession();
            session.setAttribute("name",name);
            resp.sendRedirect("/download.jsp");
        }
        System.out.println(name);
    }
}

downloadservlet

@WebFilter("/download.jsp")
public class DOwnloadFIlter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request=(HttpServletRequest)servletRequest;
        HttpServletResponse response=(HttpServletResponse)servletResponse;
        HttpSession session=request.getSession();
        String name = (String) session.getAttribute("name");
    if(name==null){
        //不是登录状态
        response.sendRedirect("/login.jsp");
    }else {
        filterChain.doFilter(servletRequest,servletResponse);
    }
    }

    @Override
    public void destroy() {

    }
}