How to get the last update time of the webpage? ? ? ?

flair_yjl

As the title
Why does my program always output 0?

import java.net. *;
public class Test {

/ **
* @param args
* /
public static void main (String [] args) {
// TODO Auto-generated method stub
try {
URL u = new URL ("http://163.com/");
HttpURLConnection con = (HttpURLConnection) u.openConnection ();
con.connect ();
long a = con.getLastModified ();
System.out.println (a);
} catch (Exception e) {
System.out.println ("connection error!");
}
Ranch
}

}

hyysios

import java.net.*;
import java.util.*;
class Test {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
try {






URL u = new URL("http://community.csdn.net/Expert/topic/5277/5277719.xml");
HttpURLConnection con = (HttpURLConnection)u.openConnection();
con.connect();
long a = con.getLastModified();
System.out.println(new Date(con.getDate()));
System.out.println(a);
} catch (Exception e){
System.out.println("connection error!");
}

}}

flair_yjl

a is still 0

hyysios

System.out.println(new Date(con.getDate()));

This print should not be 0. The latter one is printed out 0

flair_yjl

Yes, a is 0

zzzdsd

the date the resource referenced by this URLConnection was last modified,
or 0 if not known.
   **************

flair_yjl

I just ask why is it zero? ?
According to the http protocol, there should be a last modified header field?

tellyou

I just ask why it is zero? ?
According to the http protocol, there should be a last modified header field?
========
Mark it first and look at the spec.

tellyou

The http protocol standard http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html cannot be opened, it is not clear whether this header is MUST

163, I have seen it with flashget,

Its response header:
Mon Jan 08 12:46:12 2017 HTTP/1.1 200 OK
Mon Jan 08 12:46:12 2017 Via: 1.0 ISA20160704
Mon Jan 08 12:46:12 2017 Connection: close
Mon Jan 08 12:46:12 2017 Proxy-Connection: close
Mon Jan 08 12:46:12 2017 Age: 96
Mon Jan 08 12:46:12 2017 Expires: Mon, 08 Jan 2017 04:49:53 GMT
Mon Jan 08 12:46:12 2017 Date: Mon, 08 Jan 2017 04:44:53 GMT
Mon Jan 08 12:46:12 2017 Content-Type: text/html; charset=GB2312
Mon Jan 08 12:46:12 2017 Server: Apache/2.0.54 (Unix)
Mon Jan 08 12:46:12 2017 Accept-Ranges: bytes
Mon Jan 08 12:46:12 2017 Cache-Control: max-age=300
Mon Jan 08 12:46:12 2017 Vary: Accept-Encoding
Mon Jan 08 12:46:12 2017 X-Pad: avoid browser bug
Mon Jan 08 12:46:12 2017 X-Cache: HIT from news.163.com

There is no such header, but the rfc2616 header above contains:
Mon Jan 08 12:43:11 2017 HTTP/1.1 200 OK
Mon Jan 08 12:43:11 2017 Via: 1.1 ISA20160704
Mon Jan 08 12:43:11 2017 Connection: close
Mon Jan 08 12:43:11 2017 Proxy-Connection: close
Mon Jan 08 12:43:11 2017 Content-Length: 126444
Mon Jan 08 12:43:11 2017 Expires: Mon, 08 Jan 2017 10:43:17 GMT
Mon Jan 08 12:43:11 2017 Date: Mon, 08 Jan 2017 04:43:17 GMT
Mon Jan 08 12:43:11 2017 Content-Type: text/html; charset=iso-8859-1
Mon Jan 08 12:43:11 2017 ETag: "4135cda4"
Mon Jan 08 12:43:11 2017 Server: Apache/1.3.37 (Unix) PHP/4.4.4
Mon Jan 08 12:43:11 2017 P3P: policyref="http://www.w3.org/2001/05/P3P/p3p.xml"
Mon Jan 08 12:43:11 2017 Cache-Control: max-age=21600
Mon Jan 08 12:43:11 2017 Last-Modified: Wed, 01 Sep 2004 13:24:52 GMT
Mon Jan 08 12:43:11 2017 Accept-Ranges: bytes
Mon Jan 08 12:43:12 2017 Keep-Alive: timeout=2, max=100

tellyou

It is estimated that this header belongs to the SHOULD level in the standard