Add milliseconds to Java date, when milliseconds is long

Question

I am looking for the best way to add milliseconds to a Java Date when milliseconds is stored as a 'long'. Java calendar has an add function, but it only takes an 'int' as the amount.

This is one solution I am proposing...

Calendar now = Calendar.getInstance();
Calendar timeout = Calendar.getInstance();

timeout.setTime(token.getCreatedOn());
timeout.setTimeInMillis(timeout.getTimeInMillis() + token.getExpiresIn());

Any other suggestions?

Answer 1

Your solution looks nearly fine to me, actually. I originally posted an answer going via Date, when I hadn't taken getTimeInMillis and setTimeInMillis into account properly.

However, you're calling setTime and then setTimeInMillis which seems somewhat redundant to me. Your code looks equivalent to this:

Calendar timeout = Calendar.getInstance(); timeout.setTimeInMillis(token.getCreatedOn().getTime() + token.getExpiresIn()); 

A generally nicer alternative would be to use Joda Time though :) It's generally a much nicer date/time API.

Answer 2

You can also create a date with the current local date plus the number of miliseconds you need to add as Expire time

import java.util.Date;  long expiremilis = 60000l; //  1 minute // Expires in one minute from now Date expireDate = new Date(System.currentTimeMillis() + expiremilis); 

Or the same with a calendar

long expiremilis = 60000l; // 1 minute Calendar expireDate= Calendar.getInstance(); // Expires on one minute from now expireDate.setTimeInMillis(System.currentTimeMillis() + expiremilis); 

If you use an existing Date object you can do:

import java.util.Date;  long expiremilis = 60000l; // 1 minute // Expires on one minute from the date object date Date expireDate = new Date(myDate.getTime() + expiremilis); 

And with an existing Calendar Object

long expiremilis = 60000l; // 1 minute Calendar expireDate= Calendar.getInstance(); // Expires on one minute from the calendar date expireDate.setTimeInMillis(myCalendar.getTimeInMillis() + expiremilis); 

Answer 3

java.time

The java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern Date-Time API^*.

Demo using java.time, the modern API:

import java.time.Instant;

public class Main {
    public static void main(String[] args) {
        Instant createdOn = Instant.ofEpochMilli(1_622_800_000_000L);
        System.out.println(createdOn);

        Instant timeout = createdOn.plusMillis(50_000L);
        System.out.println(timeout);
    }
}

See this code run live at IdeOne.com.

Output:

2021-06-04T09:46:40Z
2021-06-04T09:47:30Z

An Instant represents an instantaneous point on the timeline in UTC. The Z in the output is the timezone designator for a zero-timezone offset. It stands for Zulu and specifies the Etc/UTC timezone (which has the timezone offset of +00:00 hours).

So, the solution to your problem would be:

Instant createdOn = token.getCreatedOn().toInstant();
Instant timeout = createdOn.plusMillis(token.getExpiresIn());

Check documentation of Date#toInstant to learn more about it.

Learn more about java.time, the modern Date-Time API^* from Trail: Date Time.

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^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.}