如何在Java tomcat服务器中获取主机地址

Question

I'm trying to get IP address from DNS like this:

InetAddress hostAddr = InetAddress.getByName("somentp.server.com");

but hostAddr is null, it seems like it can't find it. I'm doing this from a thread in Java, which is executed on a ServletContextListener in Tomcat Server. If i do this from the same thread but in a normal Java app, it works perfectly fine. The goal of all this is to use the address as argument to NTP Client API .

I don't know if it's a problem of Tomcat, some configuration or any other bug

I hope you can help me, thanks

Answer 1

As per the inetAddress#getByName docs , the static method getByName doesn't return a null unless the method throws one of the two exceptions UnknownHostException or SecurityException .

Your code in the ServletContextListener seems to be swallowing the exception. You need to debug that code and find out which exception out of the above two is being thrown by the call to getByName. Once you determine the exception type, you can take an appropriate action to correct the error reported by that exception. Eg if the exception is UnknownHostException , you might want to check the host name argument that you are passing to the method.