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Filter过滤器详解(监听器以及它们的应用)
2022-07-25 09:25:00 【Zero摄氏度】
Filter过滤器详解
1.过滤器
Fillter：过滤器，用来过滤网站的数据；
- 处理中文乱码
- 登录验证…
web服务有一些垃圾请求，后台不应该处理或者应该报错时由过滤器来过滤
2. Filter开发步骤
- 导包
- 编写过滤器
package com.qian.filter;
import javax.servlet.*;
import java.io.IOException;
//初始化：web服务器启动，就已经初始化了，随时等待过滤对象出现！
//销毁：eb服务器关闭的时候，才销毁
public class CharacterEncodingFilter implements Filter {
//init: 初始化 destroy：销毁
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("CharacterEncodingFilter初始化");
}
//chain:链
/* 1.过滤中的所有代码，在过滤特定请求的时候都会执行 2.必须要让过滤器继续同行 */
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");
System.out.println(" CharacterEncodingFilter执行前...");
filterChain.doFilter(servletRequest,servletResponse); // 让我们的请求继续走，如果不写，程序到这里就被拦截停止！
System.out.println(" CharacterEncodingFilter执行后...");
}
public void destroy() {
System.out.println("CharacterEncodingFilter销毁");
}
}
- 在web.xml中注册过滤器
<filter>
<filter-name>CharacterEncodingFilter</filter-name>
<filter-class>com.qian.filter.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<!-- 只要是/servlet下的任何请求，都会经过这个过滤器-->
<url-pattern>/servlet/*</url-pattern> </filter-mapping> 3.监听器
- 实现一个监听器的接口：（有很多种）
- 编写一个监听器，实现监听接口
package com.qian.listener;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
//统计网站在线人数：统计session
public class OnlineCountListener implements HttpSessionListener {
//创建session监听：看你的一举一动
//一旦创建Session就会触发一次这个事件
public void sessionCreated(HttpSessionEvent se) {
ServletContext ctx = se.getSession().getServletContext();
System.out.println(se.getSession().getId());
Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");
if (onlineCount==null){
onlineCount = new Integer(1);
}else {
int count = onlineCount.intValue();
onlineCount = new Integer(count+1);
}
ctx.setAttribute("OnlineCount",onlineCount);
}
//销毁session监听
//一旦销毁Seesion就会触发一次这个事件
public void sessionDestroyed(HttpSessionEvent se) {
ServletContext ctx = se.getSession().getServletContext();
se.getSession().invalidate();
Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");
if (onlineCount==null){
onlineCount = new Integer(0);
}else {
int count = onlineCount.intValue();
onlineCount = new Integer(count-1);
}
ctx.setAttribute("OnlineCount",onlineCount);
/* * Session销毁： * 1.手动销毁：getSession().invalidate(); * * 2.自动销毁---->web.xml中配置 * */
}
}
- web.xml中注册监听器
<!-- 注册监听器-->
<listener>
<listener-class>com.qian.listener.OnlineCountListener</listener-class>
</listener>
<!-- session自动销毁-->
<session-config>
<session-timeout>1</session-timeout>
</session-config>
4.过滤器、监听器的常见应用
监听器：GUI编程中经常使用
登录注销
- 用户登录之后才能进入主页，用户注销后就不能进入主页
//登录
package com.qian.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 {
//获取前端请求的参数
String username = req.getParameter("Username");
if (username.equals("admin")){
req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
resp.sendRedirect("/sys/success.jsp");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
//注销
package com.qian.servlet;
import com.qian.util.Constant;
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 {
Object user_session = req.getSession().getAttribute(Constant.USER_SESSION);
if (user_session!=null){
req.getSession().removeAttribute("USER_SESSION");
resp.sendRedirect("/login.jsp");
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
注册
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>com.qian.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.qian.servlet.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LogoutServlet</servlet-name>
<url-pattern>/servlet/logout</url-pattern>
</servlet-mapping>
<filter>
<filter-name>SysFilter</filter-name>
<filter-class>com.qian.filter.SysFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>SysFilter</filter-name>
<url-pattern>/sys/*</url-pattern>
</filter-mapping>
jsp设计
<%-- 主页
Created by IntelliJ IDEA.
User: HUAWEI
Date: 2022/4/11
Time: 16:52
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1>登录成功</h1>
<p><a href="/servlet/logout">注销</a></p>
</body>
</html>
<%-- 登录页面
Created by IntelliJ IDEA.
User: HUAWEI
Date: 2022/4/11
Time: 16:53
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>登录</title>
</head>
<body>
<h1>登录</h1>
<form action=${pageContext.request.contextPath}/servlet/login method="post">
<input type="text" name="username">
<input type="submit">
</form>
<%--页面登录---->提交请求到/servlet/login---->操作请求，成功跳转success--%>
</body>
</html>
<%--错误页面
Created by IntelliJ IDEA.
User: HUAWEI
Date: 2022/4/11
Time: 20:37
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>登录错误</title>
</head>
<body>
<h1>错误</h1>
<h3>没有权限或者用户名错误</h3>
<a href="/login.jsp">返回登录页面</a>
</body>
</html>
- 进入主页的时候要判断用户是否已经登录，要求：在过滤器中实现
package com.qian.filter;
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 {
public void init(FilterConfig filterConfig) throws ServletException {
}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest request1 = (HttpServletRequest)servletRequest;
HttpServletResponse response1 = (HttpServletResponse)servletResponse;
Object user_session = request1.getSession().getAttribute("USER_SESSION");
if (request1.getSession().getAttribute("USER_SESSION")==null){
response1.sendRedirect("/Error.jsp");
}
filterChain.doFilter(servletRequest,servletResponse);
}
public void destroy() {
}
}
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