java web过滤器防止未登录进入界面

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;

import javax.servlet.http.HttpSession;

public class LoginFilter implements Filter {

 @Override

 public void init(FilterConfig filterConfig) throws ServletException {

  // TODO Auto-generated method stub

 }

 @Override

 public void doFilter(ServletRequest request, ServletResponse response,

   FilterChain chain) throws IOException, ServletException {

  // 获得在下面代码中要用的request,response,session对象

  HttpServletRequest servletRequest = (HttpServletRequest) request;

  HttpServletResponse servletResponse = (HttpServletResponse) response;

  HttpSession session = servletRequest.getSession();

  // 获得用户请求的URI

  String path = servletRequest.getRequestURI();

  //System.out.println(path);

  // 从session里取员工工号信息

  String empId = (String) session.getAttribute("empId");

  /*创建类Constants.java，里面写的是无需过滤的页面

  for (int i = 0; i < Constants.NoFilter_Pages.length; i++) {

   if (path.indexOf(Constants.NoFilter_Pages[i]) > -1) {

    chain.doFilter(servletRequest, servletResponse);

    return;

   }

  }*/

  // 登陆页面无需过滤

  if(path.indexOf("/login.jsp") > -1) {

   chain.doFilter(servletRequest, servletResponse);

   return;

  }

  // 判断如果没有取到员工信息,就跳转到登陆页面

  if (empId == null || "".equals(empId)) {

   // 跳转到登陆页面

   servletResponse.sendRedirect("/JingXing_OA/login.jsp");

  } else {

   // 已经登陆,继续此次请求

   chain.doFilter(request, response);

  }

 }

 @Override

 public void destroy() {

  // TODO Auto-generated method stub

 }

}

2.然后在web.xml里配置需要登陆权限验证的JSP文件:

  a.如果是某个具体的JSP文件(如a.jsp)需要登陆验证：

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<!-- 配置登陆过滤器 --> <filter>   <filter-name>login</filter-name>   <filter-class>com.jingxing.oa.filter.LoginFilter</filter-class>  </filter>  <filter-mapping>   <filter-name>login</filter-name>   <url-pattern>/*</url-pattern> </filter-mapping>

b.如果是某一个目录(如a/目录)整个目录下的文件都需要登陆验证:

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<!-- 配置登陆过滤器 -->  <filter>   <filter-name>login</filter-name>   <filter-class>com.jingxing.oa.filter.LoginFilter</filter-class>  </filter>  <filter-mapping>   <filter-name>login</filter-name>   <url-pattern>/a/*</url-pattern>  </filter-mapping>