long timestamp to LocalDateTime

You need to pass timestamp in milliseconds:

long test_timestamp = 1499070300000L;
LocalDateTime triggerTime =
        LocalDateTime.ofInstant(Instant.ofEpochMilli(test_timestamp), 
                                TimeZone.getDefault().toZoneId());  

System.out.println(triggerTime);

Result:

2017-07-03T10:25

Or use ofEpochSecond instead:

long test_timestamp = 1499070300L;
LocalDateTime triggerTime =
       LocalDateTime.ofInstant(Instant.ofEpochSecond(test_timestamp),
                               TimeZone.getDefault().toZoneId());   

System.out.println(triggerTime);

Result:

2017-07-03T10:25