怎样获取网页的最后更新时间？？？？

flair_yjl

如题
我的程序怎么老是输出0呢？

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!");
                }
               
        }

}

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还是0阿

hyysios

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

这个打印出来应当不是0吧 。后面那个是打印出来0

flair_yjl

对，a是0

zzzdsd

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

flair_yjl

我就是问为什么会是零阿？？
根据http协议，应该有个last modified header field阿？

tellyou

我就是问为什么会是零阿？？
根据http协议，应该有个last modified header field阿？
========
先mark一下，在看spec.

tellyou

http协议标准的http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html打不开，不清楚这个header是否是MUST

163的，我用flashget看过了,

它的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

没有这个header，而上面那个rfc2616的header里面有：
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

估计在标准里面这个header属于SHOULD级别的