实践中filter的配备

实践中filter的配置
配置一个权限filter，拦截一切没有登录却想访问只有登录后才有的权限页面的url，我的做法如下：

  先写上一个filter：

   

package com.xll.util;

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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class RightFilter implements Filter {
	private FilterConfig filterConfig;

	public void destroy() {
	}
	public void doFilter(ServletRequest req, ServletResponse resp,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) resp;
		String uri = request.getRequestURI();
		System.out.println(uri);
		String ctx = request.getContextPath();
		System.out.println(ctx);
		uri = uri.substring(ctx.length());
		if (uri.startsWith("/admin")) {
			if (request.getSession().getAttribute("username") == null) {
				System.out.println("没有登录");
				response.sendRedirect("/VoteSystem/index.jsp");
				System.out.println("xxxxxxxxxxx");
				return ;
			} else {
				chain.doFilter(request, response);
			}
		}
	}
	public void init(FilterConfig filterConfig) throws ServletException {
		this.filterConfig = filterConfig;
	}

}

然后在web.xml中配置，这时我把这个filter的配置放在struts核心filter之前，放在之后貌似起不到你要的效果，这个还需要求解释（貌似是优先级的问题）

<filter>
		<filter-name>RightFilter</filter-name>
		<filter-class>com.xll.util.RightFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>RightFilter</filter-name>
		<url-pattern>/admin/*</url-pattern>
	</filter-mapping>
	

	<filter>								<!--定义核心Filter FilterDispatcher -->
		<filter-name>struts2</filter-name>	<!-- 定义核心Filter的名称 -->
		<filter-class>						<!--定义核心Filter的实现类 -->
			org.apache.struts2.dispatcher.FilterDispatcher
		</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>struts2</filter-name><!--核心Filter的名称 -->
		<url-pattern>/*</url-pattern><!--使用该核心Filter过滤所有的Web请求 -->
	</filter-mapping>

这样一配置，我想要拦截访问admin下所有的请求就能够实现了，注意：你的filter一定要写正确，使用filter时避免连续两次跳转，否则会报java.lang.IllegalStateException错误