Filter 過濾器

Filter :過濾器，用來過濾網站的資料：

處理中文亂碼
登錄驗證

在這里插入圖片描述

案例

public class ShowServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        resp.setCharacterEncoding("utf-8");
//        req.setCharacterEncoding("utf-8");
//        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().write("今天是4月13日");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

package com.srx.servlet.filter;


import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {

     //初始化  web服務器啟動 就已經初始化了，等待過濾的物件
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter正在初始化");

    }
    //Chain
//    1.過濾所有的代碼,在過濾特定請求的時候會執行
//    2.必須要讓過濾器維持同行
    //filterChain.doFilter(servletRequest,servletResponse);

    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執行前");
        // 讓我們的請求繼續走 ，如果不寫 程式這里就會被攔截
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("CharacterEncodingFilter執行后");


    }

    //銷毀
    public void destroy() {
        System.out.println("CharacterEncodingFilter正在銷毀");
    }
}

xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <servlet>
        <servlet-name>ShowServlet</servlet-name>
        <servlet-class>com.srx.servlet.servlet.ShowServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/show</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/servlet/show</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.srx.servlet.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/servlet/*</url-pattern>

    </filter-mapping>
</web-app>

監聽器

//統計網站在線人數：統計session
public class OnlineCountListener implements HttpSessionListener {

    //創建Session監聽
    //一單創建session就會觸發這個事件
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {

        ServletContext context1 = httpSessionEvent.getSession().getServletContext();

        //System.out.println(httpSessionEvent.getSession().getId());
        Integer onlineCount = (Integer)context1.getAttribute("onlineCount");

        if (onlineCount!=null){
            System.out.println("11111");
            int count = onlineCount.intValue();
            onlineCount= new Integer(count+1);

        } else {
            onlineCount= new Integer(1);
        }

        System.out.println(onlineCount);
         context1.setAttribute("onlineCount",onlineCount);
    }

    //銷毀session監聽
    //一旦銷毀Session就會觸發一次這個事件
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        ServletContext context = httpSessionEvent.getSession().getServletContext();

        Integer onlineCount = (Integer)context.getAttribute("OnlineCount");

        if (onlineCount==null){
            onlineCount= new Integer(0);
        }
        else {
            int count = onlineCount.intValue();
            onlineCount= new Integer(count-1);
        }

        context.setAttribute("onlineCount",onlineCount);
    }
//
//    session銷毀
//    1. 手動銷毀  getSession().invalidate();
//    2. 自動銷毀
}

xml

    <listener>
        <listener-class>com.srx.servlet.listener.OnlineCountListener</listener-class>
    </listener>

     <session-config>
         <session-timeout>1</session-timeout>
     </session-config>

jsp頁面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
  <h1> 在線人數為 <span> <%= this.getServletConfig().getServletContext().getAttribute("onlineCount") %></span> 人</h1>
  </body>
</html>

過濾器的應用

用戶登錄之后才能進入主頁！用戶注銷后就不能進入主頁了！

用戶登錄之后向session中放入用戶資料
進入主頁的時候判斷用戶是否已經登錄

登錄jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<form action="/servlet/login" method="post">
    賬號：<input type="text" name="username">
    <br>
    <input type="submit" value="登錄">
</form>

</body>
</html>

錯誤jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>錯誤</h1>
<h3>登錄失敗，請檢查你的賬號或密碼</h3>  <br>
<a href="/Login.jsp">重新登錄</a>
</body>
</html>

成功jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>主頁</h1>

<a href="/servlet/loginout">注銷</a>
</body>
</html>

登錄的servlet

package com.srx.servlet.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 LoginDemo extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {


        String useranme = req.getParameter("username");
        System.out.println(useranme);
        if (useranme.equals("admin")){
            System.out.println(useranme);
           req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            System.out.println("01010212313131");
           resp.sendRedirect("/sys/Success.jsp");
            System.out.println("0101001");
        }else {
            resp.sendRedirect("/error.jsp");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

注銷的servlet

package com.srx.servlet.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 LoginoutDemo extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        Object userSession = req.getSession().getAttribute("USER_SESSION");
        if (userSession!=null){
            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 {
        doGet(req, resp);
    }
}

過濾器的servlet

package com.srx.servlet.listener;

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 servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        HttpServletRequest Request1 = (HttpServletRequest) servletRequest;
        HttpServletResponse Response1 = (HttpServletResponse) servletResponse;

        if (Request1.getSession().getAttribute("USER_SESSION")==null){
            Response1.sendRedirect("/error.jsp");
        }

        filterChain.doFilter(Request1,Response1);

    }

    public void destroy() {

    }
}

xml配置

<servlet>
        <servlet-name>login</servlet-name>
        <servlet-class>com.srx.servlet.servlet.LoginDemo</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>login</servlet-name>
        <url-pattern>/servlet/login</url-pattern>
    </servlet-mapping>
    
    <servlet>
        <servlet-name>loginout</servlet-name>
        <servlet-class>com.srx.servlet.servlet.LoginoutDemo</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>loginout</servlet-name>
        <url-pattern>/servlet/loginout</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>sysFilter</filter-name>
        <filter-class>com.srx.servlet.listener.sysFilter</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>sysFilter</filter-name>
        <url-pattern>/sys/*</url-pattern>
    </filter-mapping>

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標籤：java

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Filter詳解

Filter 過濾器

監聽器

過濾器的應用