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：

1 2 3 4 5 6 7 8 9

<!-- 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:

1 2 3 4 5 6 7 8 9

<!-- 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>