Java web过滤器验证登录（避免未经登录进入主页）

    今天用ssh2写了个简单的系统，发现了一个问题，我这系统必须先登录成功才能进入主页，但我在浏览器里直接输入主页地址，发现也能进入，这个肯定不好，毫无安全性可言，后经查资料发现需要登录过滤器，就试了下，发现果然可以避免未经登录即可进入主页的危险，下面是我整理出的详细步骤：

1.首先写一个权限过滤filter类,实现Filter接口

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

<!-- 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:

<!-- 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>