过滤器 filter
配置文件信息
<?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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5"> <display-name></display-name> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <filter> <filter-name>myfirst</filter-name> <filter-class>com.itheima.web.filter.HelloFilter</filter-class> </filter> <filter-mapping> <filter-name>myfirst</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <filter> <display-name>FilterDemo2</display-name> <filter-name>FilterDemo2</filter-name> <filter-class>com.itheima.web.filter.FilterDemo2</filter-class> <init-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value> </init-param> <init-param> <param-name>cgx</param-name> <param-value>aj</param-value> </init-param> </filter> <filter-mapping> <filter-name>FilterDemo2</filter-name> <url-pattern>*.jsp</url-pattern> </filter-mapping> </web-app>
编写一个过滤器,实现过滤器接口 filter
package com.itheima.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; public class FilterDemo2 implements Filter { private FilterConfig config; public void destroy() { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { System.out.println("FilterDemo2放行前的代码"); //2.获取初始化参数 FilterConfig对象可以获取, 这个对象当容器调用 init(FilterConfig fConfig)时,会自动为FilterConfig赋值 /** <init-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value> </init-param>*/ String encodingValue = config.getInitParameter("encoding");//用于获取初始化参数 System.out.println(encodingValue); //2.1获取多个初始化参数 getInitParameterNames() /** * <init-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value> </init-param> <init-param> <param-name>cgx</param-name> <param-value>aj</param-value> </init-param> * */ Enumeration<String> enumss = config.getInitParameterNames();//encoding ,cgx while(enumss.hasMoreElements()){ String paramName = enumss.nextElement();//得到一个参数 <param-name>encoding</param-name> String paramValue = config.getInitParameter(paramName);//<param-value>UTF-8</param-value> System.out.println(paramName+":"+paramValue); } chain.doFilter(request, response);//放行 System.out.println("FilterDemo2放行回来后的代码"); } public void init(FilterConfig fConfig) throws ServletException { this.config = fConfig; } }
过滤器的执行顺序和mapping在web.xml里的位置有关,放前面的先执行。