- 过滤器能够对目标资源的请求和响应进行截取。
过滤器的工作方式分为四种
- request 过滤器
- forward 过滤器
- include 过滤器
- error 过滤器
- web.xml
testServlet com.nadoutong.servlet.TestServlet testServlet /testServlet test2Servlet com.nadoutong.servlet.Test2Servlet test2Servlet /test2Servlet myFilter com.nadoutong.filter.CharacterEncodingFilter myFilter /testServlet myFilter /test2Servlet
- CharacterEncodingFilter.java
package com.nadoutong.filter;
import javax.servlet.*;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
public class CharacterEncodingFilter implements Filter {
//初始化 ：web 服务器启动,就可以初始化，随时等待过滤器对象的出现
@Override
public void init(FilterConfig filterConfig) throws ServletException {
try {
System.out.println(URLEncoder.encode("CharacterEncodingFilter 初始化...","UTF-8"));
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
servletRequest.setCharacterEncoding("utf-8");
servletResponse.setCharacterEncoding("utf-8");
servletResponse.setContentType("text/html;charset=UTF-8");
//让请求继续走，如果不写程序到这里就被拦截停止了
filterChain.doFilter(servletRequest,servletResponse);
}
//销毁 web服务器关闭 ，过滤就会销毁
@Override
public void destroy() {
System.out.println("CharacterEncodingFilter 被销毁...");
}
}
例：用户登录之后进入主页,用户注销之后就不能进入主页
- 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已经登录了
- 页面情况
- web.xml
myLogin nadoutong.servlet.LoginServlet myLogin /loginServlet myLogout nadoutong.servlet.LogoutServlet myLogout /logoutServlet loginFilter nadoutong.filter.CheckLoginFilter loginFilter /page/*
- https://blog.csdn.net/m0_56981185/article/details/login.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
Title
- error.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
Title
你访问的页面不存在
返回登录页面
- success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
Title
登录成功
注销登录
- LogoutServlet.java
package nadoutong.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 {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.getSession().removeAttribute("USER_SESSION");
resp.sendRedirect("/THIRD_JAVAWEB/https://blog.csdn.net/m0_56981185/article/details/login.jsp");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- LoginServlet.java
package nadoutong.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 {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String username = req.getParameter("username");
System.out.println(username);
if (username.equals("admin")) {
req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
resp.sendRedirect("/THIRD_JAVAWEB/page/success.jsp");
}else {
resp.sendRedirect("/THIRD_JAVAWEB/https://blog.csdn.net/m0_56981185/article/details/login.jsp");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
- CheckLoginFilter.java
package nadoutong.filter;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class CheckLoginFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) servletRequest;
HttpServletResponse resp = (HttpServletResponse) servletResponse;
if (req.getSession().getAttribute("USER_SESSION")==null){
resp.sendRedirect("/THIRD_JAVAWEB/error.jsp");
}
filterChain.doFilter(servletRequest,servletResponse);
}
@Override
public void destroy() {
}
}
执行视频：
过滤器实现-验证成功才能直接访问某些页面
Listener监听器例 ：利用监听器实现 监听网站在线人数监听器有很多种，实现监听器接口即可构造一个监听器
可以看到有很多的监听接口，根据业务需要自己选择相应的监听器进行实现即可
- TestListener.java
package com.nadoutong.listener;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
//实现session 监听接口
public class TestListener implements HttpSessionListener {
// 如果session 被创建 就执行
@Override
public void sessionCreated(HttpSessionEvent se) {
//获取servletContext
ServletContext servletContext = se.getSession().getServletContext();
//获取servletContext 里的属性 OnLinenumber
Integer onLinenumber = (Integer)servletContext.getAttribute("OnLinenumber");
//如果没有该属性
if(onLinenumber==null){
//赋初始值1
onLinenumber = new Integer(1);
}else {
//如果有 则每次加一
int i = onLinenumber.intValue();
onLinenumber=new Integer(i+1);
}
// 将新的值赋予 OnLinenumber
servletContext.setAttribute("OnLinenumber",onLinenumber);
}
// 如果session 被销毁 就执行
@Override
public void sessionDestroyed(HttpSessionEvent se) {
//获取servletContext
ServletContext servletContext = se.getSession().getServletContext();
//获取servletContext 里的属性 OnLinenumber
Integer onLinenumber = (Integer)servletContext.getAttribute("OnLinenumber");
//如果没有该属性
if(onLinenumber==null){
//赋初始值1
onLinenumber = new Integer(0);
}else {
//如果有 则每次加一
int i = onLinenumber.intValue();
onLinenumber=new Integer(i-1);
}
// 将新的值赋予 OnLinenumber
servletContext.setAttribute("OnLinenumber",onLinenumber);
}
}
- web.xml 中注册监听器
com.nadoutong.listener.TestListener
编写index.jsp 测试
<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>
统计网站在线人数
网站在线人数为：${applicationScope.get("OnLinenumber")}
网站在线人数为：<%= request.getServletContext().getAttribute("OnLinenumber")%>
监听器一般在GUI 编程中用的较多
