Web常用Filter

配置web.xml 

<!-- 定义Filter -->
    <filter>
    <!-- Filter的名字 -->
    <filter-name>loginFilter</filter-name>
    <!-- Filter的实现类 -->
    <filter-class>com.sxdf.rent.servlets.LoginFilter</filter-class>
    <!-- 下面3个init-param元素配置了3个参数 -->
    <init-param>
    <param-name>encoding</param-name>
    <param-value>UTF-8</param-value>
    </init-param>
   
    <!-- 登录页面 -->
    <init-param>
    <param-name>loginPage</param-name>
    <param-value>/rent/index.jsp</param-value>
    </init-param>
   
    <!-- 登录信息处理页面 -->
    <init-param>
    <param-name>proLogin</param-name>
    <param-value>/rent/userLogin.jsp</param-value>
    </init-param>
   
    <!-- 没有session返回的界面 -->
    <init-param>
    <param-name>timeoutPage</param-name>
    <param-value>/rent/sessionTimeout.jsp</param-value>
    </init-param>
   
    <!-- 默认界面界面 -->
    <init-param>
    <param-name>defaultPage</param-name>
    <param-value>/rent/</param-value>
    </init-param>
   
   
    </filter>
    <!-- 定义Filter拦截的URL地址 -->
    <filter-mapping>
    <!-- Filter的名字 -->
    <filter-name>loginFilter</filter-name>
    <!-- Filter负责拦截的URL -->
    <url-pattern>/*</url-pattern>
    </filter-mapping>
   

JAVA代码

　　LoginFilter  还可以加一个 PermissionFilter

public class LoginFilter implements Filter {
   
    private FilterConfig config = null ;
   
    @Override
    public void destroy() {
        this.config = null ;
    }

    //过滤session中没有user的情况，既是没有登录的用户，或者闲置过久的用户。
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest)request ;
        HttpServletResponse resp = (HttpServletResponse)response;
       
        String encoding = config.getInitParameter("encoding");
        String loginPage = config.getInitParameter("loginPage");
        String proLogin = config.getInitParameter("proLogin");
        String timeoutPage = config.getInitParameter("timeoutPage");
        String defaultPage = config.getInitParameter("defaultPage");
       
        User u = (User) req.getSession().getAttribute("user");
       
        //System.out.println(req.getRequestURI());  ///rent/index.jsp
        //System.out.println(req.getRequestURL());  //http://127.0.0.1:8080/rent/index.jsp
       
        if(!PropertiesTool.getProperty("print").equals("0")) {
            System.out.println(req.getRequestURL());
        }
       
       
        //如果访问的是图片 或者 include文件夹下的文件 也可以放行
        if(check(req.getRequestURI())) {
            filterChain.doFilter(request, response);
        }
        //如果user为null 并且请求的不是登录页面 也不是 登录信息处理页面那么就跳转到首页去。
        else if( u == null && !req.getRequestURI().endsWith(loginPage) && !req.getRequestURI().endsWith(proLogin) && !req.getRequestURI().endsWith(defaultPage) && !req.getRequestURI().endsWith(timeoutPage)) {
            //forward到登录页面
            //req.getSession().setAttribute("tip" , "您还没有登录");
            resp.sendRedirect(timeoutPage);
            return ;
           
            //如果用户不可用
        } else if( u != null && !u.getIsUseable() ) {
            req.setAttribute("tip" , "用户已经被禁用");
            resp.sendRedirect("index.jsp");
            return ;
        }
       
        //“放行”请求
        else {
            filterChain.doFilter(request, response);
           
        }
   
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.config = filterConfig;
       
    }
   
    //检查链接是否是访问include文件夹或者图片文件夹
    private boolean check(String url) {
       
        String folder = PropertiesTool.getProperty("folder");
        String[] folders = folder.split(",");
        for(String str : folders ) {
            if(url.contains("/" + str.trim() + "/")) {
                //System.out.println("放行:" + url);
                return true ;
            }
        }
       
       
        return false;
    }

}