过滤器，监听器的常见应用
监听器：GUI编程中经常使用
用户登录才能进入主页，不登录就不能进入主页 -> 过滤器
- 用户登录之后，向Session中放入用户的数据
- 进入主页的时候要判断用户是否登录，要求：在过滤器中实现
LoginServlet
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取前端请求的参数
String username = req.getParameter("username");
if(username.equals("admin")){
//登录成功
req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
resp.sendRedirect("/sys/success.jsp");
}else{
//登录失败
resp.sendRedirect("/sys/error.jsp");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doPost(req, resp);
}
}
FilterServlet
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class SysFilter implements Filter {
public void init(FilterConfig filterConfig) throws ServletException {
}
public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
Object user_session = request.getSession().getAttribute("USER_SESSION");
if(user_session == null){
response.sendRedirect("/error.jsp");
}
chain.doFilter(request,response);
}
public void destroy() {
}
}
Success.jsp
<%@ page contentType="text/html; charset=UTF-8" language="java" %>
<html>
<head>
<title></title>
</head>
<body>
<%
Object user_session = request.getSession().getAttribute("USER_SESSION");
if(user_session == null){
pageContext.forward("Login.jsp");
}
%>
<h1>主页</h1>
<p><a href="/servlet/logout" target="_blank" rel="external nofollow" >注销</a> </p>
</body>
</html>
LogoutServlet
注销：直接删除Session中的USER_SESSION
public class LogoutServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Object user_session = req.getSession().getAttribute("USER_SESSION");
if(user_session != null){//登陆的
req.getSession().removeAttribute("USER_SESSION");
resp.sendRedirect("/Login.jsp");
}else{
resp.sendRedirect("/Login.jsp");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
super.doPost(req, resp);
}
}
记得在web.xml里配置Servlet和Filter
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