页面未在 Servlet/Filter 中正确重定向答案

【问题标题】：The page isn't redirecting properly in Servlet/Filter页面未在 Servlet/Filter 中正确重定向
【发布时间】：2016-07-18 10:12:33
【问题描述】：

我是 Servlet 和过滤器的新手。我正在尝试阻止所有未在我的应用程序中登录的用户。

Web.xml 文件

<filter>
        <filter-name>UserFilter</filter-name>
        <filter-class>user.UserFilter</filter-class>

    <init-param>
        <param-name>avoid-urls</param-name>
        <param-value>index.jsp, SelectDb.jsp, login.jsp</param-value>
    </init-param>

    </filter>
    <filter-mapping>
    <filter-name>UserFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

过滤器类

package user;

import java.io.IOException;
import java.util.ArrayList;
import java.util.StringTokenizer;
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 UserFilter implements Filter {

    private ArrayList<String> urlList;

    public UserFilter() {
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        String url = request.getServletPath();
        String contextPath = request.getContextPath();
        boolean allowedRequest = false;

        for (String urlList1 : urlList) {
            if (url.contains(urlList1)) {
                allowedRequest = true;
                break;
            }
        }
        if (!allowedRequest) {
            HttpSession session = request.getSession();
            if (null == session) {
                response.sendRedirect("");
            } else {
                String logged = (String) session.getAttribute("username");
                if (logged == null) {
                    response.sendRedirect(request.getContextPath() + "/dashboard/SelectDb.jsp");
                } else {
                    chain.doFilter(request, response);
                }
            }
        } else {
            chain.doFilter(request, response);
        }

    }

    @Override
    public void destroy() {
    }

    @Override
    public void init(FilterConfig config) {
        String urls = config.getInitParameter("avoid-urls");
        StringTokenizer token = new StringTokenizer(urls, ",");
        urlList = new ArrayList<>();
        while (token.hasMoreTokens()) {
            urlList.add(token.nextToken());
        }
    }

}

我可以看到页面正确地重定向到我要重定向的页面。网址正在改变。但是Firefox 表示页面没有正确重定向。消息有点像这样：Firefox has detected that the server is redirecting the request for this address in a way that will never complete. This problem can sometimes be caused by disabling or refusing to accept cookies。我不认为这个错误来自浏览器本身。因为我也尝试过其他浏览器。为什么会出现这个错误？如何解决这个错误？

【问题讨论】：

标签： java redirect servlets

【解决方案1】：

尝试替换

HttpSession session = request.getSession();

到

HttpSession session = request.getSession(false);

request.getSession() 如果还没有会话，将创建一个新会话，因此它永远不会返回 null，因此用户将被重定向到他拥有 !allowedRequest 的 selectDb url 及其进入和无限重定向

【讨论】：