appengine java中静态文件的HTTPS重定向

<filter>
    <filter-name>HttpsFilter</filter-name>
    <filter-class>com.example.HttpsFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>HttpsFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

package com.example;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HttpsFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

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

        if (!httpRequest.isSecure()) {
            String redirectUrl = "https://" + httpRequest.getServerName() + httpRequest.getRequestURI();
            httpResponse.sendRedirect(redirectUrl);
            return;
        }

        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {
    }
}