学习Java的日子 Day62 Filter过滤器

Day62 Filter过滤器

简介

Filter：过滤器，通过Filter可以拦截访问web资源的请求与响应操作。

Servlet API中提供了一个Filter接口，开发web应用时，如果编写的Java类实现了这个接口，则把这个java类称之为过滤器。他可以拦截Jsp、Servlet、静态图片文件、静态 html文件等，从而实现一些特殊的功能。

例如：实现URL级别的权限访问控制、过滤敏感词汇、压缩响应信息等一些高级功能。

服务器发送请求，通过层层过滤器，才能访问资源

在这里插入图片描述

创建步骤

创建过滤器类并实现Filter接口
在web.xml文件中配置Filter

javax.servlet.Filter接口中的方法介绍：

方法描述
init(FilterConfig fConfig) 初始化方法
doFilter(ServletRequest request, ServletResponse response, FilterChain chain) 过滤方法
destroy() 销毁方法

方法	描述
init(FilterConfig fConfig)	初始化方法
doFilter(ServletRequest request, ServletResponse response, FilterChain chain)	过滤方法
destroy()	销毁方法

1.初始Filter过滤器

创建过滤器的步骤：

1.创建Java类，实现Filter接口（javax.servlet.Filter）

2.在web.xml中配置

操作

Welcome.html

导包servlet-api.jar，在web.xml中配置首页

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>欢迎页面</h1>
    
<a href="ser01">向Servlet01发送一个请求</a>
    
</body>
</html>

Filter01

package com.qf.filter;

public class Filter01 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("Filter01 -- doFilter() -- 前");
        //chain过滤器链
        //注意：如果拦截后不调用doFilter()，请求将无法传到下一个过滤器或服务器里
        //放行
        filterChain.doFilter(servletRequest,servletResponse);

        System.out.println("Filter01 -- doFilter() -- 后");
    }

    @Override
    public void destroy() {

    }
}

Servlet01

package com.qf.servlet;

@WebServlet("/ser01")
public class Servlet01 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println("Servlet01收到了一个请求");
    }
}

在web.xml配置文件中配置过滤器信息

<?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">

    <welcome-file-list>
        <welcome-file>Welcome.html</welcome-file>
    </welcome-file-list>

    <filter>
        <filter-name>Filter01</filter-name>
        <filter-class>com.qf.filter.Filter01</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>Filter01</filter-name>
        <url-pattern>/*</url-pattern><!-- 拦截所有请求 -->
    </filter-mapping>
    
</web-app>

2.过滤器链

客户端对服务器请求之后，服务器在调用Servlet之前，会执行一组过滤器（多个过滤器），那么这组过滤器就称为一条过滤器链。

过滤器链是指在一个Web应用，可以配置多个过滤器，这多个过滤器称为过滤器链。

在这里插入图片描述

3.Filter的生命周期

3.1生命周期 - 单个过滤器

单个过滤器的生命周期：

创建：项目启动时 – 无参构造、init()

销毁：服务器正常关闭时 – destroy()

package com.qf.filter;

public class Filter01 implements Filter {

    public Filter01(){
        System.out.println("Filter01 -- Filter01()");
    }
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

        String code = filterConfig.getInitParameter("code");
        System.out.println("Filter01 -- init() -- " + code);
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        System.out.println("Filter01 -- doFilter() -- 前");
        //放行
        filterChain.doFilter(servletRequest,servletResponse);

        System.out.println("Filter01 -- doFilter() -- 后");
    }

    @Override
    public void destroy() {
        System.out.println("Filter01 -- destroy()");
    }
}

在web.xml配置文件中配置初始化参数信息 code-UTF-8

<?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">

    <welcome-file-list>
        <welcome-file>Welcome.html</welcome-file>
    </welcome-file-list>

    <filter>
        <filter-name>Filter01</filter-name>
        <filter-class>com.qf.filter.Filter01</filter-class>
        <init-param>
            <param-name>code</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>Filter01</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>

运行结果：

在这里插入图片描述

3.2 生命周期 - 多个过滤器

Filter的生命周期：

创建：项目启动时 – 无参构造、init()

销毁：服务器正常关闭时 – destroy()

Filter的创建顺序 – 不用关注：

多线程抢资源（创建顺序无序）

Filter的调用顺序 – 关注：

web.xml配置 ------> 按照配置顺序

@WebFilter配置 --> 按照类名的字典排序

经验：一般使用web.xml配置

是单例模式

//----------- Filter01 -----------------------
public class Filter01 implements Filter {
    public Filter01() {
    	System.out.println("Filter01 - Filter01()");
    }
    public void init(FilterConfig fConfig) throws ServletException {
    	System.out.println("Filter01 - init()");
	}
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    	System.out.println("Filter01执行前");
    	chain.doFilter(request, response);//放行
    	System.out.println("Filter01执行后");
	}
    
	public void destroy() { 
		System.out.println("Filter01 - destroy()");
	}
}

//----------- Filter02 -----------------------
public class Filter02 implements Filter {

	public Filter02() {
		System.out.println("Filter02 - Filter02()");
	}

	public void init(FilterConfig fConfig) throws ServletException {
		System.out.println("Filter02 - init()");
	}
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		System.out.println("Filter02执行前");
		chain.doFilter(request, response);//放行
		System.out.println("Filter02执行后");
	}
	public void destroy() { 
		System.out.println("Filter02 - destroy()");
	}
}

//----------- Filter03 -----------------------
public class Filter03 implements Filter {

	public Filter03() {
		System.out.println("Filter03 - Filter03()");
	}

	public void init(FilterConfig fConfig) throws ServletException {
		System.out.println("Filter03 - init()");
	}
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		System.out.println("Filter03执行前");
		chain.doFilter(request, response);//放行
		System.out.println("Filter03执行后");
	}
	public void destroy() { 
		System.out.println("Filter03 - destroy()");
	}
}

2.在web.xml配置文件中配置过滤器信息

<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">
    
    <welcome-file-list>
        <welcome-file>welcome.html</welcome-file>
    </welcome-file-list>
    
         <filter> 
             <filter-name>Filter01</filter-name> 
             <filter-class>com.qf.filter.Filter01</filter-class> 
             <init-param> 
                 <param-name>code</param-name> 
                 <param-value>UTF-8</param-value> 
             </init-param> 
         </filter> 
         <filter-mapping> 
             <filter-name>Filter01</filter-name> 
             <url-pattern>/*</url-pattern> 
         </filter-mapping> 
    
         <filter> 
             <filter-name>Filter02</filter-name> 
             <filter-class>com.qf.filter.Filter02</filter-class> 
             <init-param> 
                 <param-name>code</param-name> 
                 <param-value>UTF-8</param-value> 
             </init-param> 
         </filter> 
         <filter-mapping> 
             <filter-name>Filter02</filter-name> 
             <url-pattern>/*</url-pattern> 
         </filter-mapping> 
    
         <filter> 
             <filter-name>Filter03</filter-name> 
             <filter-class>com.qf.filter.Filter03</filter-class> 
             <init-param> 
                 <param-name>code</param-name> 
                 <param-value>UTF-8</param-value> 
             </init-param> 
         </filter> 
         <filter-mapping> 
             <filter-name>Filter03</filter-name> 
             <url-pattern>/*</url-pattern> 
         </filter-mapping> 
    
</web-app>

3.3 注解配置过滤器（简化配置）

创建顺序：创建顺序无序

执行顺序：按照类名的顺序执行

注意：一般不使用这个

@WebFilter(value="/*",initParams={@WebInitParam(name="encode",value="UTF-8")})
public class EncodeFilter implements Filter {
    ...
}

4.案例

在这里插入图片描述

4.1 案例一：编码过滤器

解决请求和响应乱码问题

package com.qf.filter;

public class CodeFilter implements Filter {
    private String code;
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

        //获取web.xml中该过滤器的初始化属性
         code = filterConfig.getInitParameter("code");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        servletRequest.setCharacterEncoding(code);
        servletResponse.setContentType("text/html;charset="+code);
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {

    }
}

   <filter>
        <filter-name>CodeFilter</filter-name>
        <filter-class>com.qf.filter.CodeFilter</filter-class>
        <init-param>
            <param-name>code</param-name><!-- 初始化参数名 -->
            <param-value>UTF-8</param-value><!-- 初始化参数值 -->
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>CodeFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

4.2 案例二：登录权限过滤器

解决权限的统一控制问题，没有登录，就不能直接跳转到其他详情页面

package com.qf.filter;

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

   }

   @Override
   public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

       //强转
       HttpServletRequest request= (HttpServletRequest) servletRequest;
       HttpServletResponse response= (HttpServletResponse) servletResponse;

       //获取请求地址
       String uri = request.getRequestURI();
       
       if (uri.equals("/Day19_war_exploded/")   ||
               uri.contains("register.jsp")   ||
               uri.contains("RegisterServlet")   ||
               uri.contains("welcome.html")   ||
               uri.contains("login.jsp")   ||
               uri.contains("CodeServlet")   ||
               uri.contains("LoginServlet") ){
           filterChain.doFilter(request,response);
       }else {
           //如果登录成功，会存储session凭证
           HttpSession session = request.getSession();
           String username = (String) session.getAttribute("username");
           String name = (String) session.getAttribute("name");
           String role = (String) session.getAttribute("role");

           if (username==null||name==null||role==null){//session凭证为空，不允许登录
               response.sendRedirect("login.jsp");
           }else {
               if(!role.equals("teacher") && uri.contains("GetStuListServlet")){
                   response.sendRedirect("login.jsp");
               }else{
                   filterChain.doFilter(request,response);
               }
           }
       }

   }

   @Override
   public void destroy() {

   }
}

    <filter>
        <filter-name>LoginFilter</filter-name>
        <filter-class>com.qf.filter.LoginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>LoginFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

4.3 案例三：关键字过滤器

解决文档内的一个敏感词汇

Welcome.html，提交建议

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>首页</title>
</head>
<body>
    <a href="proposal.jsp">提交建议</a>
</body>
</html>

proposal.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    
<h1>建议页面</h1>
<form action="ProposalServlet" method="post">
    建议：<input type="text" name="info"><br>
    <input type="submit" value="提交"/>
    <input type="button" value="返回" οnclick="goIndex()"/>
</form>

<script type="text/javascript">
    function goIndex(){
        window.location = "Welcome.html";
    }
</script>
</body>
</html>

MyHttpServletRequestWrapper

请求包装类，处理敏感词

package com.qf.wrapper;

public class MyHttpServletRequestWrapper extends HttpServletRequestWrapper {
    //有参构造
    public MyHttpServletRequestWrapper(HttpServletRequest request) {
        super(request);
    }

    //子类重写
    @Override
    public String getParameter(String name) {
        String value = super.getParameter(name);
        //把尖括号替换成字符尖括号，替换后不会认为是html里的尖括号符号
        value = value.replaceAll("<", "&lt;");
        value = value.replaceAll(">", "&gt;");
        value = value.replaceAll("傻逼", "**");

        return value;

    }
}

SensitiveWordsFilter

package com.qf.filter;

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

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        //创建请求包装类对象（注意：对象中包含了请求对象）
        MyHttpServletRequestWrapper myHttpServletRequestWrapper = new MyHttpServletRequestWrapper(request);

        //放行的是请求包装类对象
        filterChain.doFilter(myHttpServletRequestWrapper,response);

    }

    @Override
    public void destroy() {

    }
}

    <filter>
        <filter-name>SensitiveWordsFilter</filter-name>
        <filter-class>com.qf.filter.SensitiveWordsFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SensitiveWordsFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>