Filter+Listener

标签：Listener com void javax Filter import servlet public

11.Filter （重点）

Filter：过滤器，用来过滤网站的数据；

处理中文乱码
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Filter开发步骤：

导包

编写过滤器

导包不要错；

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>JavaWeb-02-Servlet</artifactId>
        <groupId>com.github</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>Filer</artifactId>

    <dependencies>
        <!--   Servlet 依赖   -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>
        <!--        JSP 依赖   -->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>
        <!--        JSTL表达式的依赖-->
        <dependency>
            <groupId>javax.servlet.jsp.jstl</groupId>
            <artifactId>jstl-api</artifactId>
            <version>1.2</version>
        </dependency>
        <!--        standard标签库-->
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
        <!--    连接数据库-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
    </dependencies>

</project>

实现Filter接口，重写对应的方法即可；

package com.github.filter;

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

public class CharacterEncodingFilter implements Filter {
    
    /**
     * 初始化：web服务器启动，就以及初始化了，随时等待过滤对象出现！
     */
    public void init(FilterConfig filterConfig) {
        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
     *    chain.doFilter(request,response);
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");

        System.out.println("CharacterEncodingFilter执行前....");
        // 让我们的请求继续走，如果不写，程序到这里就被拦截停止！
        chain.doFilter(request,response);
        System.out.println("CharacterEncodingFilter执行后....");
    }

    /**
     * 销毁：web服务器关闭的时候，过滤会销毁
     */
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁");
    }
}

在web.xml中配置 Filter；

<?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">

    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.github.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <!--只要是 /servlet的任何请求，会经过这个过滤器-->
        <url-pattern>/servlet/*</url-pattern>
        <!--<url-pattern>/*</url-pattern>-->
    </filter-mapping>

</web-app>

12.监听器

实现一个监听器的接口；（有N种）

编写一个监听器；

实现监听器的接口…

package com.github.listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * @Description: 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！
     * @param se
     */
    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Session就会触发一次这个事件！
     * @param se
     */
    public void sessionDestroyed(HttpSessionEvent se) {
        ServletContext ctx = se.getSession().getServletContext();

        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中注册监听器；

<!--注册监听器-->
<listener>
    <listener-class>com.github.listener.OnlineCountListener</listener-class>
</listener>

看情况是否使用！

13.过滤器.监听器常见应用

监听器：GUI编程中经常使用；

package com.github.listener;

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class TestPanel {
    public static void main(String[] args) {
        // 新建一个窗体
        Frame frame = new Frame("建军节快乐");  
        // 面板
        Panel panel = new Panel(null);
        // 设置窗体的布局
        frame.setLayout(null); 

        frame.setBounds(300,300,500,500);
        // 设置背景颜色1
        frame.setBackground(new Color(68, 227, 177)); 

        panel.setBounds(50,50,300,300);
        // 设置背景颜色2
        panel.setBackground(new Color(255, 242,0)); 

        frame.add(panel);

        frame.setVisible(true);

        // 监听事件，监听关闭事件
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                super.windowClosing(e);
            }
        });

    }
}

案例：用户登录之后才能进入主页！用户注销后就不能进入主页了！

用户登录之后，向Sesison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；要求：在过滤器中实现！

因为：个人tomcat配置的为 /Filer 如下图：

LoginServlet.java

package com.github.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 IOException, ServletException {
        super.doGet(req,resp);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 获取前端请求的参数
        String username = req.getParameter("username");

        // 登陆成功
        if("admin".equals(username)){
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect("/Filer/sys/success.jsp");

        } else {    // 登陆失败
            resp.sendRedirect("/Filer/error.jsp");
        }
    }
}

LogoutServlet.java

package com.github.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 {
        Object user_session = req.getSession().getAttribute("USER_SESSION");
        if(user_session!=null){
            req.getSession().removeAttribute("USER_SESSION");
            resp.sendRedirect("/Filer/Login.jsp");
        } else {
            resp.sendRedirect("/Filer/Login.jsp");
        }
    }

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

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

<h1>登陆界面</h1>
<form action="/Filer/servlet/login" method="post">
    <input type="text" name="username">
    <input type="submit">
</form>

</body>
</html>

success.jsp

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

<%--<%--%>
<%--    Object userSession = request.getSession().getAttribute("USER_SESSION");--%>
<%--    if(userSession==null){--%>
<%--        response.sendRedirect("Filer/Login.jsp");--%>
<%--    }--%>
<%--%>--%>

<h1>主页</h1>

<p><a href="/Filer/servlet/logout">注销</a> </p>

</body>
</html>

error.jsp

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

<h1>错误</h1>
<h3>没有权限，用户名错误</h3>

<p> <a href="/Filer/Login.jsp">返回登录主页</a></p>

</body>
</html>

进行登录注销无法登录判断；
Constant.java

package com.github.Util;

public class Constant {
    public static String USER_SESSION="USER_SESSION";
}

SysFilter.java

package com.github.listener;

import com.github.Util.Constant;

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 req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;

        if (request.getSession().getAttribute(Constant.USER_SESSION)==null){
            response.sendRedirect("/Filer/error.jsp");
        }

        chain.doFilter(request,response);
    }

    public void destroy() {

    }
}

web.xml

<?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>LoginServlet</servlet-name>
        <servlet-class>com.github.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.github.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.github.listener.SysFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SysFilter</filter-name>
        <url-pattern>/sys/*</url-pattern>
    </filter-mapping>
    
</web-app>

运行结果如下：

标签：Listener,com,void,javax,Filter,import,servlet,public
From： https://www.cnblogs.com/qqingniao/p/17213650.html

11.Filter （重点）

12.监听器

13.过滤器.监听器常见应用

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