filter_config_DHCP的主要功能「建议收藏」

在Filter的init方法中有一个参数FilterConfig.

FilterConfig作用也是获取Filter的相关配置信息:

1.初始化参数的获取

String getInitparameter(String name);

Enumeration EnumerngetInitParameterNames();

2.Filter的名称获取

getFilterName();

3.ServletContext对象的获取

getServletContext();

测试:创建一个DemoFilter2的类文件.

package cn.itcast.web.filter;

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import com.sun.net.httpserver.Filter.Chain;

//Filter入门
//1.创建一个类,实现Filter接口
//2.重写方法
//3.在web.xml文件中配置
public class DemoFilter2 implements Filter{
	public void destroy() {
	}
	
	//用来过滤的方法
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		System.out.println("DemoFilter2进行过滤操作...");
		//放行
		chain.doFilter(request, response);
	}

	public void init(FilterConfig filterConfig) throws ServletException {
		//1.获取Filter名称
		String filterName = filterConfig.getFilterName();
		System.out.println(filterName);
		
		//2.获取初始化参数
		String encoding = filterConfig.getInitParameter("encoding");	//根据指定名称获取
		System.out.println(encoding);
		
		Enumeration<String> names = filterConfig.getInitParameterNames();//获取所有名称
		while(names.hasMoreElements()){
			System.out.println(names.nextElement());
		}
		
		//3.获取ServletContext对象
		filterConfig.getServletContext();
	}
}

然后修改web.xml的配置文件.

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
	
	<!-- Filter入门 -->
	<filter>
		<filter-name>demoFilter</filter-name>
		<filter-class>cn.itcast.web.filter.DemoFilter</filter-class>
	</filter>
	
	<filter>
		<filter-name>demoFilter2</filter-name>
		<filter-class>cn.itcast.web.filter.DemoFilter2</filter-class>
		
		<!-- 初始化参数 -->
		<init-param>
			<param-name>encoding</param-name>
			<param-value>utf-8</param-value>
		</init-param>
		<init-param>
			<param-name>username</param-name>
			<param-value>tom</param-value>
		</init-param>
		
	</filter>
	
	<filter-mapping>
		<filter-name>demoFilter2</filter-name>
		<url-pattern>/index.jsp</url-pattern>	<!-- 访问index.jsp页面会被DemoFilter过滤掉 -->
	</filter-mapping>
	
	<filter-mapping>
		<filter-name>demoFilter</filter-name>
		<url-pattern>/index.jsp</url-pattern>	<!-- 访问index.jsp页面会被DemoFilter过滤掉 -->
	</filter-mapping>
	
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

运行到服务器上,控制台会输出.