web中定义过滤器验证登录（未登录没有权限访问页面）

在进行web系统开发时，我们需要对用户的请求进行拦截，避免非法用户登录

配置字符集过滤器（Filter）

1、定义过滤器LoginFilter，实现Filter接口，并重新里面的init()、doFilter()和 destroy()方法

2、在doFilter()中判断用户是否登录系统了，只有合法登录后才能访问系统

分析： 首先分析session中是否有用户的信息，

            有则放行，

            没有，判断是否是登录请求或者是登录提交请求，

            是则放行，

            不是则跳转到登录页面

3、分析代码

                HttpServletRequest req = (HttpServletRequest) request;HttpServletResponse resp = (HttpServletResponse) response;// 获得当前请求的URIString nowPath = req.getRequestURI();if (req.getSession().getAttribute(Constant.SESSION_USER) == null) {if ("/lbjn_mybatis/login.do".equals(nowPath)|| "/lbjn_mybatis/loginSubmit.do".equals(nowPath)) {chain.doFilter(req, resp);return;} else {resp.sendRedirect(req.getContextPath() + "/login.do");return;}}chain.doFilter(request, response);

4、在web.xml中配置过滤器的信息

<!-- 拦截非法登录 --><filter><filter-name>LoginFilter</filter-name><filter-class>cn.demo.filter.LoginFilter</filter-class></filter><filter-mapping><filter-name>LoginFilter</filter-name><url-pattern>*.do</url-pattern></filter-mapping>

LoginFilter.java源码：

package cn.demo.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 cn.ilfy.lbjn_mybatis.constant.Constant;public class LoginFilter implements Filter {@Overridepublic void destroy() {}@Overridepublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {HttpServletRequest req = (HttpServletRequest) request;HttpServletResponse resp = (HttpServletResponse) response;// 获得当前请求的URIString nowPath = req.getRequestURI();if (req.getSession().getAttribute(Constant.SESSION_USER) == null) {if ("/lbjn_mybatis/login.do".equals(nowPath)|| "/lbjn_mybatis/loginSubmit.do".equals(nowPath)) {chain.doFilter(req, resp);return;} else {resp.sendRedirect(req.getContextPath() + "/login.do");return;}}chain.doFilter(request, response);}@Overridepublic void init(FilterConfig arg0) throws ServletException {}}