Time is Complicated: java.time

July 12, 2020

Time is complicated, really complicated. We have historically grown calendar systems, historical units, timezones, limelight savings times, etc. On top of that, we have precise atomic clocks and astronomical time definitions drifting apart and need periodical corrections, like with leap seconds.

Agreeing On Time
Figure 1. Agreeing On Time
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Time Does Not Flow Evenly

May 31, 2020

You are working on some system and you need some kind of timestamp in milli- or nanoseconds. Nothing easier than that. In Unix you might use clock_gettime and in Java System.currentTimeMillis() and of your go.

// Forgive me my C, I probably got things wrong =)
#include <sys/time.h>
#include <stdint.h>

int64_t time_stamp_nanos(){
    struct timespec current;
    clock_gettime(CLOCK_REALTIME, &current);
    return current.tv_sec * 1000000000 + current.tv_nsec;
}
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Terminal Utilities I Often Use

May 17, 2020

In this blog post, I just list a few Unixy terminal utilities I often use. If you are a terminal veteran this will be boring for you. If you rarely use the terminal, it might have a utility or two you are not aware of yet.

I’m not giving a tutorial on the commands. Google for more details or read the man pages =). It is just to let you know that these tools exist.

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Slack Java API and the Data Non Problem

May 9, 2020

Recently I had the "joy" to work with the Slack Java API. I felt that this Java API is tedious and an example of an API which create busy work for little benefit. Let me show first how the API is used:

var slack = Slack.getInstance();
var methods = slack.methods();

var channeId = "C424242";
var request = ChatPostMessageRequest.builder()
        .channel(channeId)
        .text(":wave: Hi from a bot written in Java!")
        .build();

var response = methods.chatPostMessage(request);
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Keep Time Explicit

May 2, 2020

In a lot of software is operations are depending on time. For example creating invoices, statistics, showing the latest news so on so forth. In this blog post, I use an example summing up bought items in the last week. We might have multiple layers in our system, like database access, places to do extra processing, and a web interface. I’m using C# here, but it applies to most mainstream languages. As you can see, to get the right database records the cure uses the current time.

Example Database Access:
public class Purchases
{
    public IList<Purchase> LastWeeksPurchases()
    {
        // Assume more complex queries, let's say joins with users, applied coupons, discounts at the time and god knows what
        return Database.InTransaction(conn => conn.Query<Purchase>(@"select * from purchases
            where dateTime < current_timestamp
            and (current_timestamp + INTERVAL '-7 day') < dateTime
            order by dateTime").ToList());
    }
}
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