Java HTTP client getting time from NTP server

Question

I'm trying to write an HTTP client, and I need to get the time from an NTP server I found here: https://tf.nist.gov/tf-cgi/servers.cgi

This is my Java code:

String getTime(){
    String time = "";
    try{
        Socket timeSocket = new Socket("time-a-g.nist.gov",37);
        BufferedReader timeIn = new BufferedReader(new InputStreamReader(timeSocket.getInputStream()));
        time = timeIn.readLine();
        timeSocket.close();
        timeIn.close();
    }
    catch(IOException e){
        e.printStackTrace();
    }
    return time;
}

I'm not getting any errors, but the string I'm getting back is null, can anyone help?

Just search for "[java] ntp" on SO: https://stackoverflow.com/search?q=%5Bjava%5D+ntp, eg. https://stackoverflow.com/questions/38711730/how-can-i-access-ntp-clock-in-java/39309568 — ChrLipp, Jan 14 '22 at 07:34

Remy Lebeau · Accepted Answer · 2022-01-14T15:44:55.873

2

TCP (and UDP) port 37, which you are connecting to, is used for the TIME protocol (RFC 868). In this protocol, times are sent as a single binary 32bit integer in network byte order.

UDP port 123 is used for the NTP protocol (RFCs 1059, 1119, 1305, 5905). In this protocol, times are sent as a series of binary messages.

You can't read either type of data as text with BufferedReader.ReadLine().

edited Jan 14 '22 at 15:44

answered Jan 14 '22 at 07:29

Remy Lebeau

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thanks, how would I be able to read it then? – Anonymous_programmer2458 Jan 14 '22 at 14:04
For the `TIME` protocol, try `DataInputStream.readInt()`. The `NTP` protocol is vastly more complex. – Remy Lebeau Jan 14 '22 at 15:48

Java HTTP client getting time from NTP server

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