Filter 简单应用实例求详解

Question

web.xml

AdminFilter
szy.shopping.filter.AdminFilter

url
/admin/login.jsp

<filter-mapping>
    <filter-name>AdminFilter</filter-name>
    <url-pattern>/admin/index.jsp</url-pattern>
</filter-mapping>

AdminFilter.java

public class AdminFilter implements Filter{
String url = "/";
@Override
public void destroy() {

}

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    HttpServletResponse res = (HttpServletResponse) response;
    HttpSession session = req.getSession();
    if (session.getAttribute("admin") == null) {
        res.sendRedirect(req.getContextPath() + url);
        return ;
    }
    chain.doFilter(request, response);
}

@Override
public void init(FilterConfig config) throws ServletException {
    url = config.getInitParameter("url");
}

}

能不能详细说明以上两段代码的具体解释？大致的流程是怎么样的？

[b]问题补充：[/b]
lianj_lee所说的这个权限判断是我写程序调用，还是它自动根据XML来调用验证是否登录？

还有

AdminFilter
szy.shopping.filter.AdminFilter

url
/admin/login.jsp

AdminFilter
/admin/index.jsp

可否在详细说明？谢谢～

Answer 1

简单的一个权限判断，admin用户登录以后会在session里面放入一个变量，变量名“admin”， 所有在filter里面判断这个在session里面是否存在，如果不存在，则跳转到admin用户登陆页。登陆页地址是，这个[color=red]web应用地址[/color] 加上 [color=red]具体页面地址[/color] 具体页面地址是通过 filter的初始化参数传入的!

回答完毕！