该页面在Servlet /过滤器中无法正确重定向

Question

我是Servlet和Filter的新手。 我试图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());
        }
    }

}

我可以看到页面正在正确重定向到我要重定向的页面。 网址正在更改。 但是Firefox表示页面无法正确重定向。 该消息有点像这样： 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 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 。 我认为此错误不是来自浏览器本身。 因为我也尝试过其他浏览器。 为什么会出现这个错误？ 如何解决此错误？

Answer 1

尝试更换

HttpSession session = request.getSession();

至

HttpSession session = request.getSession(false);

如果没有会话，则request.getSession()将创建一个新会话，因此它将永远不会返回null，因此，用户将被重定向到他具有!allowedRequest及其进入和无限重定向的selectDb url !allowedRequest