Filter过滤器周期、Filter拦截过滤、Filter执行链

来源：互联网发布：uml数据库建模编辑：程序博客网时间：2024/05/01 14:55

Servlet过滤器的概念：
Servlet过滤器本身并不生成请求和响应对象，它只提供过滤作用。

Servlet过滤器能够在Servlet被调用之前检查Request对象，修改Request Header和Request内容。

在Servlet被调用之后检查Response对象，修改Response Header和Response内容。

Servlet过滤器负责过滤的Web组件可以是Servlet、JSP或HTML文件。

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来看一个简单小例子
Filter也是需要在web.xml进行配置：

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://java.sun.com/xml/ns/javaee"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"    id="WebApp_ID" version="2.5">    <filter>        <filter-name>helloFilter</filter-name>        <filter-class>com.safly.HelloFilter</filter-class>        <init-param>            <param-name>name</param-name>            <param-value>root</param-value>        </init-param>    </filter>    <filter-mapping>        <filter-name>helloFilter</filter-name>        <url-pattern>/test.jsp</url-pattern>    </filter-mapping></web-app>

HelloFilter

package com.safly;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class HelloFilter implements Filter{    public void destroy() {        System.out.println("destroy...");    }    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        System.out.println("doFilter");        chain.doFilter(request, response);    }    //加载web应用时，即被创建    public void init(FilterConfig filterConfig) throws ServletException {        System.out.println("init...");    }}

test.jsp页面只有一行字输出

浏览器输出：
http://localhost:8080/day01/test.jsp

这里写图片描述

Web服务器启动，根据web.xml配置，创建注册的Filter实例对象，创建完毕后，调用init方法，该法只执行一次，下次请求时，会调用doFilter，关闭服务器调用destroy

来看另一个简单小例子
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我们来看下login.jsp页面吧–里面有用户名、密码

<body><font color="red">${requestScope.message }</font>    <form action="hello.jsp" method="post">        username:<input type="text" name="username" value="${param.username }"/>        password:<input type="password" name="password"/>        <input type="submit" value="Submit"/>    </form></body>

提交后跳转到hello.jsp页面，如果验证成功，就提示hello界面

<body> Hello:${param.username }</body>

条件是在跳转到hello.jsp页面之前，需要进行拦截验证，UsernameFilter和PasswordFilter进行拦截hello.jsp页面
PasswordFilter

    <context-param>        <param-name>password</param-name>        <param-value>1234</param-value>    </context-param>    <filter>        <filter-name>UsernameFilter</filter-name>        <filter-class>com.safly.UsernameFilter</filter-class>        <init-param>            <param-name>username</param-name>            <param-value>Tom</param-value>        </init-param>    </filter>    <filter-mapping>        <filter-name>UsernameFilter</filter-name>        <url-pattern>/hello.jsp</url-pattern>    </filter-mapping>    <!-- -->    <filter>        <filter-name>PasswordFilter</filter-name>        <filter-class>com.safly.PasswordFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>PasswordFilter</filter-name>        <url-pattern>/hello.jsp</url-pattern>    </filter-mapping>

UsernameFilter在web.xml中username：Tom，如果在login.jsp页面输入的用户名为Tom，那么就会去继续验证密码是否正确，如果输入的用户名字不是Tom,就转发到login.jsp页面

package com.safly;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class UsernameFilter implements Filter {    public void destroy() {    }    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        String initUser = filterConfig.getInitParameter("username");        String username = request.getParameter("username");        if (!initUser.equals(username)) {            request.setAttribute("message", "用户名不正确");            request.getRequestDispatcher("/login.jsp").forward(request, response);            return;        }        chain.doFilter(request, response);    }    private FilterConfig filterConfig;    public void init(FilterConfig filterConfig) throws ServletException {        this.filterConfig = filterConfig;    }}

PasswordFilter如果web.xml中的password：1234，如果在login.jsp输入的密码不是1234，就转发到login.jsp,如果密码也输入正确，就进入到hello.jsp页面进行欢迎提示

package com.safly;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class PasswordFilter implements Filter {    public void destroy() {    }    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        String initPassword = filterConfig.getServletContext().getInitParameter("password");        String password = request.getParameter("password");        if (!initPassword.equals(password)) {            request.setAttribute("message", "密码不正确");            request.getRequestDispatcher("/login.jsp").forward(request, response);            return;        }        chain.doFilter(request, response);    }    private FilterConfig filterConfig;    public void init(FilterConfig filterConfig) throws ServletException {        this.filterConfig = filterConfig;    }}

以下是4种情况：
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Filter执行链流程

首先定义一个hello.jsp界面，里面只有一个链接跳转到second.jsp界面

<body><a href="second.jsp">To Test Page</a></body>

但是在跳转到second.jsp界面做了2个拦截

<filter>        <filter-name>HelloFilter</filter-name>        <filter-class>com.safly.HelloFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>HelloFilter</filter-name>        <url-pattern>/second.jsp</url-pattern>    </filter-mapping>    <filter>        <filter-name>SecondFilter</filter-name>        <filter-class>com.safly.SecondFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>SecondFilter</filter-name>        <url-pattern>/second.jsp</url-pattern>    </filter-mapping>

HelloFilter

package com.safly;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class HelloFilter implements Filter {    public void destroy() {    }    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        System.out.println("before helloFilter'chain");        chain.doFilter(request, response);        System.out.println("after hellofilter'chain");    }    public void init(FilterConfig filterConfig) throws ServletException {    }}

SecondFilter

package com.safly;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class SecondFilter implements Filter {    public void destroy() {     }    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        System.out.println("before secondFilter'chain");        chain.doFilter(request, response);        System.out.println("after secondFilter'chain");    }    public void init(FilterConfig filterConfig) throws ServletException {    }}

浏览器输入
http://localhost:8080/day01/second.jsp

log日志输出如下：

before helloFilter'chainbefore secondFilter'chainsecond.jspafter secondFilter'chainafter hellofilter'chain

通过截图来看下Filter链执行的流程吧
这里写图片描述

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