Exception in thread "main" javax.naming.CommunicationException: Could not obtain connection to any of these urls: 192.168.17.105:1099 and discovery failed with error: ...

下面的代码出现java.lang.NullPointerException at example.jdbc.main (jdbc.java:50)Exception in thread "main" Init Error:javax.naming.AuthenticationException [Root ... javax.naming.AuthenticationException [Root ...