How to Convert Bson Timestamp from Mongo changestream to UTC date format in Java?

Question

eg: clusterTime = TimeStamp{value= 6948482818288648193, seconds = 16754329210, inc= 1}

When I read the value from document.getClusterTime().toString() the value returned is bson timestamp. And I want to convert this into UTC time format.

Answer 1

The BSON timestamp value is a 64 bits number where the first 32 bits denote a count of seconds since the Unix epoch of 1970-01-01 at 00:00 UTC.

Given below is an excerpt from the mongoDB documentation:

Timestamps

BSON has a special timestamp type for internal MongoDB use and is not associated with the regular Date type. This internal timestamp type is a 64 bit value where:

• the most significant 32 bits are a time_t value (seconds since the Unix epoch)
• the least significant 32 bits are an incrementing ordinal for operations within a given second.

So for your example:

    long timestampValue = 6_948_482_818_288_648_193L;
    
    long unixTimestamp = timestampValue >> 32;
    Instant timestamp = Instant.ofEpochSecond(unixTimestamp);
    
    System.out.println(timestamp);

Output:

2021-04-07T18:22:07Z

The printed result is in UTC, denoted by the trailing Z.

Link: BSON Types - MongoDB Manual