springmvc 过滤器问题 ，求解！

springmvc 过滤器问题 ，求解！

首先是Controller:代码如下：

package com.test.spring.filter;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.filter.OncePerRequestFilter;

/** * 登录过滤 * * @author geloin * @date 2012-4-10 下午2:37:38 */
public class SessionFilter extends OncePerRequestFilter {

    /* * (non-Javadoc) * * @see * org.springframework.web.filter.OncePerRequestFilter#doFilterInternal( * javax.servlet.http.HttpServletRequest, * javax.servlet.http.HttpServletResponse, javax.servlet.FilterChain) */
    @Override
    protected void doFilterInternal(HttpServletRequest request,
            HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {

        // 不过滤的uri
        String[] notFilter = new String[] { "login.html", "index.html" };

        // 请求的uri
        String uri = request.getRequestURI();

        // uri中包含background时才进行过滤
        if (uri.indexOf("background") != -1) {
            // 是否过滤
            boolean doFilter = true;
            for (String s : notFilter) {
                if (uri.indexOf(s) != -1) {
                    // 如果uri中包含不过滤的uri，则不进行过滤
                    doFilter = false;
                    break;
                }
            }
            if (doFilter) {
                // 执行过滤
                // 从session中获取登录者实体
                Object obj = request.getSession().getAttribute("loginedUser");
                if (null == obj) {
                    // 如果session中不存在登录者实体，则弹出框提示重新登录
                    // 设置request和response的字符集，防止乱码
                    request.setCharacterEncoding("UTF-8");
                    response.setCharacterEncoding("UTF-8");
                    PrintWriter out = response.getWriter();
                    String loginPage = "....";
                    StringBuilder builder = new StringBuilder();
                    builder.append("<script type=\"text/javascript\">");
                    builder.append("alert('网页过期，请重新登录！');");
                    builder.append("window.top.location.href='");
                    builder.append(loginPage);
                    builder.append("';");
                    builder.append("</script>");
                    out.print(builder.toString());
                } else {
                    // 如果session中存在登录者实体，则继续
                    filterChain.doFilter(request, response);
                }
            } else {
                // 如果不执行过滤，则继续
                filterChain.doFilter(request, response);
            }
        } else {
            // 如果uri中不包含background，则继续
            filterChain.doFilter(request, response);
        }
    }

}

然后是在web中配置：

<filter>
    <filter-name>sessionFilter</filter-name>
    <filter-class>com.test.spring.filter.SessionFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>sessionFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

但是我还是不明白，为啥经常用在编码，登录问题上面，如怎样过滤一个不想登录的用户？希望大家看到此文章能帮帮我，谢谢了。