URLconnection.getLastModified cannot identify file changes after connection

Question

In my code, I am using URLconnection.getLastModified to watch for file changes. Unfortunately, when the file changes after the URLconnection is made, it does not recognize the file changes. Any ideas on how to make this work?
Thanks
public FileChangeMonitor(URL fileURL) throws IOException {
targetURLconnection = fileURL.openConnection();
targetURLconnection.setUseCaches(false);// This didn't seem to help - can be deleted.
public static void main(String[] args) throws InterruptedException {
FileChangeMonitor testFileChangeMonitor = null;
try {
URL MyDataFile = new URL("http://localhost/MyDataFile.xml");
testFileChangeMonitor = new FileChangeMonitor(MyDataFile);
} catch (IOException i) {
testFileChangeMonitor.start();
@Override
public void run() {
long lm = targetURLconnection.getLastModified();
long lm2 = 0;
try {
while (true) {
Thread.sleep(POLL_INTERVAL);
lm2 = targetURLconnection.getLastModified();
if (lm2 != lm) {
flag = FLAG_CHANGED;
lm = lm2;
fireStateChanged();
System.out.println("MyDataFile Changed!!!");
} catch (InterruptedException e) {
e.printStackTrace();
}

Answer 1

If (hypothetically speaking) you had an HTTP URL (which of course points to a resource in general but it might happen to be a file in your case), then a common way to examine its last-modified date is to send an HTTP HEAD request and examine the headers in the response.