File last access time and last modified time in java?

Question

In my application I read file using following method,

public void readFIleData(String path) {
    BufferedReader br = null;
    try {
        String sCurrentLine;
        br = new BufferedReader(new FileReader(path));
        while ((sCurrentLine = br.readLine()) != null) {
            System.out.println("Data : "+sCurrentLine);
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (br != null)br.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

Also I get last access time and last modified time of the file using following method,

public void getFIleInfo(String path) {
    Path file = Paths.get(path);
    try {
        BasicFileAttributes attrs = Files.readAttributes(file, BasicFileAttributes.class);
        FileTime accessTime = attrs.lastAccessTime();
        System.out.println("accessTime : "+accessTime.toMillis());
        FileTime modifiedTime = attrs.lastModifiedTime();
        System.out.println("modifiedTime : "+modifiedTime.toMillis());
    } catch (IOException e) {
        e.printStackTrace();
    }
}

I ran above methods in following order,

1-> getFIleInfo()
2-> readFIleData()
3-> getFIleInfo()

I got following as output,

accessTime : 1462943491685
modifiedTime : 1462943925846
Data : erteuyuittdgfdfghjkhw5643rtrr66664fdghf
accessTime : 1462943491685
modifiedTime : 1462943925846

Here is output times in string format,

accessTime : 2016-05-11T05:11:31.685881Z
modifiedTime : 2016-05-11T07:39:28.237884Z
Data : erteuyuittdgfdfghjkhw5643rtrr66LE229F1HBQ664fdghf
accessTime : 2016-05-11T05:11:31.685881Z
modifiedTime : 2016-05-11T07:39:28.237884Z

I have a doubt about this output because access time remains the same as before reading the data of the file. Can somebody please explain to me what is actually mean by last access time and last modified time in java?

Answer 1

First, let's focus on what these things mean.

Access - the last time the file was read, i.e., the last time the file data was accessed.

Modify - the last time the file was modified (content has been modified), i.e., time when file data last modified.

Change - the last time meta data of the file was changed (e.g. permissions), i.e., time when file status was last changed.

Edit. The access time IS changing. I suggest you use Thread.sleep(100) or something and then see if this problem persists. If it does, the culprit would have to the be the OS you are running since Java simply reads from the filesystem. @Serge Ballesta's comments should give an understanding about the Windows NTFS having an option to disable writing every change made to the file attributes back to the hard drive for performance reasons. There is actually more to this.

From [docs],

NTFS delays updates to the last access time for a file by up to one hour after the last access. NTFS also permits last access time updates to be disabled. Last access time is not updated on NTFS volumes by default.

Following is some data from running the script on mac os x.

calling getFileInfo() at: 11.4.2016 3:13:08:738
    accessTime : 11.4.2016 3:12:53:0
    modifiedTime : 29.10.2015 1:49:14:0
--------------------
sleeping for 100ms
--------------------
calling readFIleData() at: 11.4.2016 3:13:08:873
--------------------
sleeping for 100ms
--------------------
re-calling getFileInfo() at: 11.4.2016 3:13:08:977
    accessTime : 11.4.2016 3:13:08:0 <---- READING FILE CHANGES ACCESS TIME
    modifiedTime : 29.10.2015 1:49:14:0
--------------------
sleeping for 100ms
--------------------
re-calling getFileInfo() at: 11.4.2016 3:13:09:81
    accessTime : 11.4.2016 3:13:08:0 <---- READING FILE ATTRIBUTES DOES NOT CHANGE ACCESS TIME
    modifiedTime : 29.10.2015 1:49:14:0 

---

To enhance clarity, you can convert the milliseconds you have, to something more readable. The following code snippet will elaborate on that.

long accessTimeSinceEpoch = Files.readAttributes(file, BasicFileAttributes.class).lastAccessTime().toMillis();

Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(accessTimeSinceEpoch);

int mYear = calendar.get(Calendar.YEAR);
int mMonth = calendar.get(Calendar.MONTH);
int mDay = calendar.get(Calendar.DAY_OF_MONTH);

int mHour = calendar.get(Calendar.HOUR);
int mMin = calendar.get(Calendar.MINUTE);
int mSec = calendar.get(Calendar.SECOND);
int mMilisec = calendar.get(Calendar.MILLISECOND);
String st = mDay + "." + mMonth + "." + mYear + " " + mHour + ":" + mMin + ":" + mSec + ":" + mMilisec;