javaWeb过滤器Filter（二）

客官°小女子只卖身不卖艺 2024-04-07 15:41 85阅读 0赞

#### javaWeb过滤器Filter ####

*  一、FilterChain 过滤器链
 *  二、Filter的生命周期
 *   *  1、生命周期流程
     *  2、代码展示
 *  三、FilterConfig对象说明
 *  四、Filter配置
 *   *  1、匹配规则
     *  2、servlet-name 标签
     *  3、dispatcher 标签

## 一、FilterChain 过滤器链 ##

多个Filter对同一个资源进行拦截就可以形成过滤器链，同一个资源是指的匹配路径一致  
多个Filter过滤器是根据配置的顺序来执行，谁在前，先执行谁

## 二、Filter的生命周期 ##

### 1、生命周期流程 ###

和servlet 生命周期类似：实例化-》初始化->服务-》销毁

Filter的生命周期  
服务器启动时，会创建Filter对象， 并调用init方法，只调用一次  
当访问资源的时，路径与Filter的拦截路径匹配，会执行Filter的doFilter方法  
当服务器关闭时，会调用Filter 的destroy方法进行销毁

### 2、代码展示 ###

package com.heihei;
    
    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 MyFilter implements Filter{
        
    
    	@Override
    	public void destroy() {
        
    		System.out.println("Filter destroy ");
    		
    	}
    
    	@Override
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
    			throws IOException, ServletException {
        
    		System.out.println("拦截开始");
    		
    		//放行
    		chain.doFilter(request, response);
    		System.out.println("结束拦截,资源过滤后，回来了");
    		
    	}
    
    	@Override
    	public void init(FilterConfig arg0) throws ServletException {
        
    		System.out.println("Filter init ");
    		
    	}
    
    }

## 三、FilterConfig对象说明 ##

Filter初始化方法init上的一个参数 ，就是FilterConfig对象

public interface Filter {
        
        void init(FilterConfig var1) throws ServletException;
    
        void doFilter(ServletRequest var1, ServletResponse var2, FilterChain var3) throws IOException, ServletException;
    
        void destroy();
    }

MyFilterConfig

package com.heihei;
    
    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 MyFilterConfig implements Filter{
        
    
    	private FilterConfig config;
    	@Override
    	public void init(FilterConfig config) throws ServletException {
        
    		this.config = config;
    		
    	}
    
    	@Override
    	public void doFilter(ServletRequest req, ServletResponse rsp, FilterChain chain)
    			throws IOException, ServletException {
        
    		//通过FilterConfig对象获取配置文件中的初始化信息
    		String coding = config.getInitParameter("encoding");
    		System.out.println(coding);
    		req.setCharacterEncoding(coding);
    		chain.doFilter(req, rsp);
    		
    	}
    	@Override
    	public void destroy() {
        
    		// TODO Auto-generated method stub
    		
    	}
    
    }

ServletDemo

package com.heihei;
    
    import java.io.IOException;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class ServletDemo extends HttpServlet{
        
    	
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
    		System.out.println("ServletDemo");
    	}
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
    		// TODO Auto-generated method stub
    		super.doPost(req, resp);
    	}
    
    }

web.xml

<?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_3_0.xsd" id="WebApp_ID" version="3.0">
      
      <filter>
      	<filter-name>MyFilterConfig</filter-name>
      	<filter-class>com.heihei.MyFilterConfig</filter-class>
      	<init-param>
    		<param-name>encoding</param-name>
    		<param-value>UTF-8</param-value>  	
      	</init-param>
      </filter>
      
      <filter-mapping>
      	<filter-name>MyFilterConfig</filter-name>
      	<url-pattern>/*</url-pattern>
      </filter-mapping>
      
      
      <servlet>
      	<servlet-name>ServletDemo</servlet-name>
      	<servlet-class>com.heihei.ServletDemo</servlet-class>
      </servlet>
      <servlet-mapping>
      	<servlet-name>ServletDemo</servlet-name>
      	<url-pattern>/ServletDemo</url-pattern>
      </servlet-mapping>
    </web-app>

## 四、Filter配置 ##

### 1、匹配规则 ###

在web.xm文件中，<url-pattern>标签的匹配规则：
    完全匹配	 以"/demo"，不包含通配符
    目录匹配		以"/"开头，以"*"结束
    扩展名匹配：	 *.xxxx，不能写成 /*.xxx ，比如 *.do

### 2、servlet-name 标签 ###

也可以直接通过配置<servlet-name>标签，来关联到servlet对应的servlet-mapping配置，从而达到拦截的目的
    <filter-mapping>
      	<filter-name>MyFilterConfig</filter-name>
    	<servlet-name>ServletDemo</servlet-name>
      </filter-mapping>

### 3、dispatcher 标签 ###

<dispatcher>标签，默认是request请求，可以写多个dispatcher标签，比如：
     <filter-mapping>
      	<filter-name>MyFilterConfig</filter-name>
      	****
    	<dispatcher>REQUEST</dispatcher>
    	<dispatcher>FORWARD</dispatcher>
      </filter-mapping>
    
    REQUEST:默认值,只过滤客户端请求和重定向
    
    FORWARD:只过滤转发请求