HTTP Status 500 -


type Exception report

message

description The server encountered an internal error that prevented it from fulfilling this request.

exception
java.lang.NullPointerException
    cc.openhome.model.UserService.isInvalidUsername(UserService.java:27)
    cc.openhome.controller.Register.doPost(Register.java:46)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:644)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    cc.openhome.web.EscapeFilter.doFilter(EscapeFilter.java:23)
    cc.openhome.web.EncodingFilter.doFilter(EncodingFilter.java:34)


note The full stack trace of the root cause is available in the Apache Tomcat/8.0.12 logs.


Apache Tomcat/8.0.12

26： public boolean isInvalidUsername(String username) {
               27：     for (String file : new File(USERS).list()) {
               28：     if (file.equals(username)) {
               29：       return true;
               30：                  }
               31：           }
               32：          return false;
               33：        }
从上面的错误信息看是这段代码有错，我就debug了一下，显示的是Source not found.,但是不知道该怎么解决，求大神赐教！

可以了耶，感谢万分！

谢谢！