15-Filter 过滤器

本文仅供学习交流

1、Filter什么是过滤器

1、 Filter过滤器它是JavaWeb的三大组件之一。三大组件分别是，Servlet程序、Listener监听器、Fiter过滤器 2、Filter过滤器它是JavaEE的规范。也就是接口
3、Filter过滤器它的作用是↵ 拦截请求，过滤响应。
拦截请求常见的应用场景有
1、权限检查
2、日记操作
3、事务管理
等等

2、Filter的初体验

要求：在你的web工程下，有一个admin目录。这个admin目录下的所有资源(html页面、jpg图片、jsp文件、等等)都必 须是用户登录之后才允许访问。
思考:根据之前我们学过内容。我们知道，用户登录之后都会把用户登录的信息保存到Session域中。所以要检查用户是否 登录，可以判断Session中否包含有用户登录的信息即可!!!
简单演示：

新建web/admin下新建a.jsp

<%--
  Created by IntelliJ IDEA.
  User: lenovo
  Date: 2021/9/5
  Time: 下午 06:29
  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>
    <%
        Object user=session.getAttribute("user");
        //如果等于null，说明还没有登录
        if (user==null){
            request.getRequestDispatcher("/login.jsp").forward(request,response);
            return;
        }
    %>
    我是a.jsp文件
</body>
</html>

新建web/login.jsp

<%--
  Created by IntelliJ IDEA.
  User: lenovo
  Date: 2021/9/5
  Time: 下午 06:38
  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>
    这是登录页面。login.jsp页面
</body>
</html>

原理

15-Filter 过滤器_java

新建src/com.filter/AdminFilter

package com.filter;


import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class AdminFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    /**
     * doFilter方法，专门用于拦截请求。可以做权限检查
     * @param servletRequest
     * @param servletResponse
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest= (HttpServletRequest) servletRequest;
        HttpSession session=httpServletRequest.getSession();
        Object user=session.getAttribute("user");//导入service包
        //如果等于null，说明还没有登录
        if (user==null){
            servletRequest.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
            return;
        }else {
            //让程序继续往下访问用户的目标资源
            filterChain.doFilter(servletRequest,servletResponse);
        }

    }

    @Override
    public void destroy() {

    }
}

配置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">
    <!--filter标签用于配置一个Filter过滤器    -->
    <filter>
        <!-- 给filter起一个别名       -->
        <filter-name>AdminFilter</filter-name>
        <!-- 配置filter的全类名      -->
        <filter-class>com.filter.AdminFilter</filter-class>
    </filter>
    <!-- filter-mapping 配置Filter过滤器的拦截路径 -->
    <filter-mapping>
        <!-- filter-name 表示当前拦截路径给哪个filter使用      -->
        <filter-name>AdminFilter</filter-name>
        <!-- url-pattern配置拦截路径
            / 表示请求地址为：http//ip:port/工程路径/    映射到IDEA的web目录
            /admin/* 表示请求地址为：http//ip:port/工程路径/admin/*
        -->
        <url-pattern>/admin/*</url-pattern>
    </filter-mapping>
</web-app>

结果

15-Filter 过滤器_javaweb_02


Filter 过滤器的使用步骤

1、编写一个类去实现Filter接口

2、实现过滤方法doFilter()

3、到web.xm1中去配置Filter的拦截路径

补充

新建com/servlet/LoginServlet

package com.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 {
        resp.setContentType("text/html;charset=UTF-8");
        String username=req.getParameter("username");
        String password=req.getParameter("password");
        if ("wzg168".equals(username)&&"123456".equals(password)){
            req.getSession().setAttribute("user",username);
            resp.getWriter().write("登录 成功！！！");
        }else {
            req.getRequestDispatcher("/login.jsp").forward(req,resp);
        }
    }
}

配置web.xml

<servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>com.servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/loginServlet</url-pattern>
    </servlet-mapping>

修改 login.jsp

<%--
  Created by IntelliJ IDEA.
  User: lenovo
  Date: 2021/9/5
  Time: 下午 06:38
  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>
    这是登录页面。login.jsp页面
    <form action="http://localhost:8080/15_filter/loginServlet" method="get">
        用户名：<input type="text" name="username"><br>
        密  码：<input type="password" name="password"><br>
        <input type="submit"><br>
    </form>
</body>
</html>

3.Filter的生命周期

Filter的生命周期包含几个方法
1、构造器方法
2、 init初始化方法
第1，2步，在web工程启动的时候执行(Filter已经创建)
3、doFilter过滤方法
第3步，每次拦截到请求，就会执行
4、destroy销毁
第4步，停止web工程的时候，就会执行(停止web工程，也会销毁Filter过滤器)

修改 AdminFilter

package com.filter;


import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class AdminFilter implements Filter {
    public AdminFilter(){
        System.out.println("1.Filter构造器方法AdminFilter()");
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("2.Filter的init(FilterConfig filterConfig) 初始化");
    }

    /**
     * doFilter方法，专门用于拦截请求。可以做权限检查
     * @param servletRequest
     * @param servletResponse
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("3.Filter的doFilter() 过滤");
        HttpServletRequest httpServletRequest= (HttpServletRequest) servletRequest;
        HttpSession session=httpServletRequest.getSession();
        Object user=session.getAttribute("user");//导入service包
        //如果等于null，说明还没有登录
        if (user==null){
            servletRequest.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
            return;
        }else {
            //让程序继续往下访问用户的目标资源
            filterChain.doFilter(servletRequest,servletResponse);
        }

    }

    @Override
    public void destroy() {
        System.out.println("4.Filter的destroy() 销毁方法");
    }
}

结果

15-Filter 过滤器_filter_03

15-Filter 过滤器_filter_04

15-Filter 过滤器_filter_05

4、FilterConfig 类

FilterConfig类见名知义，它是Filter过滤器的配置文件类。
Tomcat每次创建Filter的时候，也会同时创建一个FilterConfig类，这里包含了Filter配置文件的配置信息。
FilterConfig类的作用是获取fiter过滤器的配置内容
1、获取Filter的名称filter-name的内容
2、获取在Filter 中配置的init-param初始化参数
3、获取ServletContext对象

修改 web.xml

<filter>
        <!-- 给filter起一个别名       -->
        <filter-name>AdminFilter</filter-name>
        <!-- 配置filter的全类名      -->
        <filter-class>com.filter.AdminFilter</filter-class>
        <init-param>
            <param-name>username</param-name>
            <param-value>root</param-value>
        </init-param>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql://localhost:3306/test</param-value>
        </init-param>
    </filter>

修改 AdminFilter

package com.filter;


import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class AdminFilter implements Filter {
    public AdminFilter(){
        System.out.println("1.Filter构造器方法AdminFilter()");
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("2.Filter的init(FilterConfig filterConfig) 初始化");
//        1、获取Filter的名称filter-name的内容
        System.out.println("filter-name的值是："+filterConfig.getFilterName());
//        2、获取在Filter 中配置的init-param初始化参数
        System.out.println("初始化参数username的值是："+filterConfig.getInitParameter("username"));
        System.out.println("初始化参数username的值是："+filterConfig.getInitParameter("url"));
//        3、获取ServletContext对象
        System.out.println(filterConfig.getServletContext());
    }

    /**
     * doFilter方法，专门用于拦截请求。可以做权限检查
     * @param servletRequest
     * @param servletResponse
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("3.Filter的doFilter() 过滤");
        HttpServletRequest httpServletRequest= (HttpServletRequest) servletRequest;
        HttpSession session=httpServletRequest.getSession();
        Object user=session.getAttribute("user");//导入service包
        //如果等于null，说明还没有登录
        if (user==null){
            servletRequest.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
            return;
        }else {
            //让程序继续往下访问用户的目标资源
            filterChain.doFilter(servletRequest,servletResponse);
        }

    }

    @Override
    public void destroy() {
        System.out.println("4.Filter的destroy() 销毁方法");
    }
}

结果

15-Filter 过滤器_java_06

5、FilterChain 过滤器链

15-Filter 过滤器_filter_07

新建filter/Filter1

package com.filter;

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

public class Filter1 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("Filter1 前置代码");
        System.out.println("Filter1线程"+Thread.currentThread().getName());
        System.out.println("Filter1 "+servletRequest.getParameter("username"));
        servletRequest.setAttribute("key1","value1");
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("Filter1线程"+Thread.currentThread().getName());
        System.out.println("Filter1 后置代码");
    }

    @Override
    public void destroy() {

    }
}

新建filter/Filter2

package com.filter;

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

public class Filter2 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("Filter2 前置代码");
        System.out.println("Filter2线程"+Thread.currentThread().getName());
        System.out.println("Filter2 "+servletRequest.getParameter("username"));
        System.out.println("Filter2取Filter1中保存的数据是："+servletRequest.getAttribute("key1"));
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("Filter2线程"+Thread.currentThread().getName());
        System.out.println("Filter2 后置代码");
    }

    @Override
    public void destroy() {

    }
}

配置web.xml 执行顺序和配置顺序一样

<filter>
        <filter-name>Filter1</filter-name>
        <filter-class>com.filter.Filter1</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>Filter1</filter-name>
        <url-pattern>/target.jsp</url-pattern>
    </filter-mapping>

    <filter>
        <filter-name>Filter2</filter-name>
        <filter-class>com.filter.Filter2</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>Filter2</filter-name>
        <url-pattern>/target.jsp</url-pattern>
    </filter-mapping>

新建web/target.jsp

<%--
  Created by IntelliJ IDEA.
  User: lenovo
  Date: 2021/9/5
  Time: 下午 08:48
  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>
    <%
        System.out.println("target.jsp页面执行了");
        System.out.println("target.jsp线程"+Thread.currentThread().getName());
        System.out.println("target.jsp "+request.getParameter("username"));

    %>
</body>
</html>

结果

15-Filter 过滤器_xml_08

6、Filter的拦截路径

-精确匹配

<url-pattern>/target.jsp</url-pattern>

以上配置的路径，表示请求地址必须为:http:/ip:port/工程路径/target.jsp

-目录匹配

<url-pattern>/admin/*</url-pattern>

以上配置的路径，表示请求地址必须为:http://ip:port/工程路径/admin/*

-后缀名匹配

<url-pattern>*.html</url-pattern>

以上配置的路径，表示请求地址必须以.html结尾才会拦截到。

<url-pattern>*.do</url-pattern>

以上配置的路径，表示请求地址必须以.do结尾才会拦截到。

<url-pattern>*.action</url-pattern>

以上配置的路径，表示请求地址必须以.action结尾才会拦截到。
注意：不能以/打头
Filter过滤器它只关心请求的地址是否匹配，不关心请求的资源是否存在！！

演示

访问http://localhost:8080/15_filter/target.abc

修改web.xml

<filter-mapping>
        <filter-name>Filter2</filter-name>
        <url-pattern>*.abc</url-pattern>
    </filter-mapping>

结果

15-Filter 过滤器_ide_09