一。web监听器：监听特殊事件的发生
1.监听实现步骤
a。写一个java类，实现特定的接口，重写相关方法
b。在web.xml中，牌配置
<listener>
<listener-class>com.listener.MyContextLisenter</listener-class>
</listener>
c.注解方式：在java类上写一个@WebLisenter
2.可以在web.xml中可以配置servetContext初始化的参数
<context-param>
<param-name>basePath</param-name>
<param-value>http://localhost:8888/StudentManager/</param-value>
</context-param>
在程序中获取方式：sce.getServletContext().getInitParameter("basePath");
3.三种监听：请求监听（ServletRequestListener），会话监听（HttpSessionListener），上下文监听（ServletContextListener）
二。过滤器
1、特点：在服务器中第一个被执行，可以拦截任意指定的路径请求
2.用于项目中的非法访问，字符集设置等等
3.实现步骤：
a.写一个java程序，实现Filter接口，重写方法
b.在web.xml中配置
<filter>
<filter-name>charfilter</filter-name>
<filter-class>com.filter.CharSetFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>charfilter</filter-name>
<!-- 拦截根目录下的所有请求 -->
<url-pattern>/*</url-pattern>
</filter-mapping>
c.dofilter方法里面的最后一句，应该将请求继续放行china.doFilter(req,resp);
web.xml配置文件
<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="/2001/XMLSchema-instance" xmlns="/xml/ns/javaee" xsi:schemaLocation="/xml/ns/javaee /xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1"><display-name>javaweb06</display-name><!-- <listener> --><!-- <listener-class>com.listener.MyRequestListener</listener-class> --><!-- </listener> --><context-param><param-name>basePath</param-name><param-value>http://localhost:8888/StudentManager/</param-value></context-param><filter><filter-name>charset</filter-name><filter-class>com.filter.CharSetFilter</filter-class></filter><filter-mapping><filter-name>charset</filter-name><url-pattern>/*</url-pattern></filter-mapping><servlet><servlet-name>loginservlet</servlet-name><servlet-class>com.control.LoginServlet</servlet-class></servlet><servlet-mapping><servlet-name>loginservlet</servlet-name><url-pattern>/login</url-pattern></servlet-mapping><servlet><servlet-name>loginservlet2</servlet-name><servlet-class>com.control.LoginServlet2</servlet-class></servlet><servlet-mapping><servlet-name>loginservlet2</servlet-name><url-pattern>/login2</url-pattern></servlet-mapping><welcome-file-list><welcome-file>index.html</welcome-file><welcome-file>index.htm</welcome-file><welcome-file>index.jsp</welcome-file><welcome-file>default.html</welcome-file><welcome-file>default.htm</welcome-file><welcome-file>default.jsp</welcome-file></welcome-file-list></web-app>
实例1：
package com.listener;import javax.servlet.ServletRequestEvent;import javax.servlet.ServletRequestListener;public class MyRequestListener implements ServletRequestListener{@Overridepublic void requestInitialized(ServletRequestEvent sre) {sre.getServletContext();sre.getServletRequest();System.out.println("请求开始");}@Overridepublic void requestDestroyed(ServletRequestEvent sre) {System.out.println("请求结束");}}
实例2：
package com.listener;import javax.servlet.ServletContext;import javax.servlet.annotation.WebListener;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;@WebListenerpublic class MySessionListener implements HttpSessionListener{@Overridepublic void sessionCreated(HttpSessionEvent se) {String path = se.getSession().getServletContext().getInitParameter("basePath");System.out.println("初始化参数为："+path);ServletContext app = se.getSession().getServletContext();Integer online = (Integer)app.getAttribute("online");if(online==null){online = 0;}System.out.println("当前在线人数是："+ ++online);app.setAttribute("online", online);}@Overridepublic void sessionDestroyed(HttpSessionEvent se) {ServletContext app = se.getSession().getServletContext();Integer online = (Integer)app.getAttribute("online");System.out.println("当前在线人数为："+ --online);app.setAttribute("online", online);}}
实例3：
package com.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.annotation.WebFilter;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;@WebFilter("/student/*")public class IsLoginFilter implements Filter{@Overridepublic void doFilter(ServletRequest req, ServletResponse resp, FilterChain arg2)throws IOException, ServletException {//1.从session中获取用户信息HttpServletRequest request = (HttpServletRequest) req;HttpServletResponse response = (HttpServletResponse) resp;String username = (String) request.getSession().getAttribute("username");System.out.println(request.getRequestURI());if(request.getRequestURI().endsWith("/login.jsp")||request.getRequestURI().endsWith("/login3")){arg2.doFilter(req, resp);return;}if(username==null){//非法登录response.sendRedirect("login.jsp");}else{arg2.doFilter(req, resp);}}}
实例4：
package com.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.annotation.WebFilter;/*** 将所有请求的字符集统一修改* @author allen*/@WebFilter("/*")public class CharSetFilter implements Filter{@Overridepublic void doFilter(ServletRequest req, ServletResponse resp, FilterChain arg2)throws IOException, ServletException {System.out.println("请求字符集修改为utf-8");req.setCharacterEncoding("utf-8");arg2.doFilter(req,resp);//将请求继续往下放行}}
