How to get a meaningful result from subtracting 2 nanoTime objects?

Question

I created a filter that monitors the length of a request.

long start = System.nanoTime();

...

long end = System.nanoTime();

How can I get the number of milliseconds from this now?

Answer 1

(end - start) / 1000000

1 microsecond = 1000 nanoseconds

1 millisecond = 1000 microseconds

Note, that the result will be rounded down, but you usually don't get true nanosecond accuracy anyway (accuracy depends on the OS). From the Javadoc on nanoTime():

This method provides nanosecond precision, but not necessarily nanosecond accuracy.

Answer 2

Also note that you can use the TimeUnit class to help with conversion. With older versions of Java, the following code might be an example to transform a processing time into some other time format:

long startTime = System.nanoTime();

//Processing in-between.

long endTime = System.nanoTime();
long duration = endTime - startTime;
duration = TimeUnit.SECONDS.convert(duration, TimeUnit.NANOSECONDS);

Note that newer versions of Java have shortcuts in the TimeUnit class.

The above sample will turn nanoseconds long into seconds. Also note that this truncates it so you do lose some precision. Therefore, if you switch to minutes then you will lose the precision of seconds. If you want to get a result of "12 minutes and 32 seconds" then you would have to do further processing with this solution.