过滤器、监听器常见应用

监听器：GUI（图形界面编程）编码中经常使用

Filter实现权限拦截：

用户登录之后才能登录首页！用户注销之后就不能进入主页了！

登录页面：

package com.kk.servlet;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;public class LoginServlet extends  HttpServlet{@Overrideprotected 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")){//登陆成功//登陆成功，把数据放在Session中的Attribute中req.getSession().setAttribute(Constant.USER_SESSION,req.getSession().getId());//重定向(跳转页面)resp.sendRedirect("/sys/success.jsp");}else{//登陆失败resp.sendRedirect("/error.jsp");}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

注销页面：

package com.kk.servlet;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;public class LogoutServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Object user_session = req.getSession().getAttribute(Constant.USER_SESSION);if(user_session!=null){req.getSession().removeAttribute(Constant.USER_SESSION);resp.sendRedirect("/Login.jsp");}else{resp.sendRedirect("/Login.jsp");}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

常量：

package com.kk.servlet;public class Constant {public final static  String USER_SESSION = "USER_SESSION";
}

过滤器：

package com.kk.listener;import com.kk.servlet.Constant;import javax.servlet.*;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;public class SysFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic 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 (request.getSession().getAttribute(Constant.USER_SESSION)==null){response.sendRedirect("/error.jsp");}chain.doFilter(request,response);}@Overridepublic void destroy() {}
}

登录页面jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>Title</title>
</head>
<body>
<h1>登陆</h1>
<form action="/servlet/login" method="post"><input type="text" name="username"><input type="submit">
</form>
</body>
</html>

登录成功jsp

<%@ page import="com.kk.servlet.Constant" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>Title</title>
</head>
<body><%--<%--%>
<%--    Object user_session = request.getSession().getAttribute(Constant.USER_SESSION);--%>
<%--    if (user_session==null){--%>
<%--        response.sendRedirect("/error.jsp");--%>
<%--    }--%>
<%--%>--%><h1>主页</h1>
<p><a href="/servlet/logout">注销</a></p>
</body>
</html>

登录失败jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>Title</title>
</head>
<body>
<h1>错误</h1>
<h3>没有权限，用户名错误!</h3>
<a href="/Login.jsp">返回登陆页面</a>
</body>
</html>

xml

<servlet><servlet-name>LoginServlet</servlet-name><servlet-class>com.kk.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping><servlet-name>LoginServlet</servlet-name><url-pattern>/servlet/login</url-pattern>
</servlet-mapping><servlet><servlet-name>LogoutServlet</servlet-name><servlet-class>com.kk.servlet.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping><servlet-name>LogoutServlet</servlet-name><url-pattern>/servlet/logout</url-pattern>
</servlet-mapping><!--只要是/sys的任何请求，都会经过这个过滤器-->
<filter><filter-name>SysFilter</filter-name><filter-class>com.kk.listener.SysFilter</filter-class>
</filter>
<filter-mapping><filter-name>SysFilter</filter-name><url-pattern>/sys/*</url-pattern>
</filter-mapping>

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过滤器、监听器常见应用（源码解析）

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