Java中应用Filter对权限和Session控制

package com.drp.util.filter; 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 AuthFilter implements Filter {public void destroy() {}public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,FilterChain filterChain) throws IOException, ServletException {/** 1,doFilter方法的第一个参数为ServletRequest对象。此对象给过滤器提供了对进入的信息（包括*   表单数据、cookie和HTTP请求头）的完全访问。第二个参数为ServletResponse，通常在简单的过*   滤器中忽略此参数。最后一个参数为FilterChain，此参数用来调用servlet或JSP页。*/HttpServletRequest request = (HttpServletRequest)servletRequest; /** 如果处理HTTP请求，并且需要访问诸如getHeader或getCookies等在ServletRequest中*   无法得到的方法，就要把此request对象构造成HttpServletRequest*/HttpServletResponse response = (HttpServletResponse)servletResponse;String currentURL = request.getRequestURI(); //取得根目录所对应的绝对路径:String targetURL = currentURL.substring(currentURL.indexOf("/", 1), currentURL.length()); //截取到当前文件名用于比较HttpSession session = request.getSession(false); if (!"/login.jsp".equals(targetURL)) {//判断当前页是否是重定向以后的登录页面页面，如果是就不做session的判断，防止出现死循环if (session == null || session.getAttribute("user") == null) {//*用户登录以后需手动添加sessionSystem.out.println("request.getContextPath()=" + request.getContextPath()); response.sendRedirect(request.getContextPath() + "/login.jsp"); //如果session为空表示用户没有登录就重定向到login.jsp页面return; }}//加入filter链继续向下执行filterChain.doFilter(request, response); /**  调用FilterChain对象的doFilter方法。Filter接口的doFilter方法取一个FilterChain对象作*    为它 的一个参数。在调用此对象的doFilter方法时，激活下一个相关的过滤器。如果没有另*    一个过滤器与servlet或JSP页面关联，则servlet或JSP页面被激活。*/}public void init(FilterConfig filterConfig) throws ServletException {}}

＜filter＞＜filter-name＞AuthFilter＜/filter-name＞＜filter-class＞com.drp.util.filter.AuthFilter＜/filter-class＞＜/filter＞＜filter-mapping＞＜filter-name＞AuthFilter＜/filter-name＞＜url-pattern＞*.jsp＜/url-pattern＞//表示对所有jsp文件有效＜/filter-mapping＞