Microstream on Helidon

Someone at work recently asked the crowd, if there are any experience at all with MicroStream without success. And I also must admit at this point I’ve never even heard about it.

I digged into it and apparently they are working hand-in-hand with the developers of the Helidon project to integrate it into it:

I briefly touched Helidon in previous experiment, after reading about it for the first time in this book about domain-driven design, but never created a complete showcase. It’s about time to change this and delve into Helidon once again.


Helidon actually comes in two flavors, but we will focus on the MicroProfile or just MP version of it. The documentation is fairly good and with the provided archetypes the first steps are made quickly.

Since I wanted to integrate this into my usual kata, I basically took my todo example and just added Helidon to it.

How to successfully compile it?

Let us start with the easy problems: The Helidon CLI cannot find the main class:

Helidon project is not supported: The required 'mainClass' property is missing.

During my research I’ve found many projects that defined their own, but apparently all it takes is this:


How to actually start it?

Helidon also comes with Helidon CLI, that can start the application and then continuously watches files for changes and restarts when necessary - the so called devloop.

On my first try I was greeted with a really cryptic error message:

loop failed helidon-cli-maven-plugin must be configured as an extension

After a bit of a try out and some more googling I finally narrowed it down and it is really just a configuration problem coupled with my lack of knowledge how Maven extensions are supposed to work:

    <extensions>true</extensions> (1)
1 This is all that is required.

Once I got the devloop running the startup and also the reload after a change runs flawlessly most of the time.

No beans found?

Unfortunately, Helidon refused to pick any JAX-RS applications and I found this goodie here in my application log:

There are no JAX-RS applications or resources. Maybe you forgot META-INF/beans.xml file?"

Looks like I am kind of spoiled by Quarkus, because it really took me a while to understand what is going on here. Alas, the solution is quite easy - I just had to configure Jandex properly:


Config is ignored?

Apparently, Helidon ignores my microprofile-config.properties and its content and to make things worse not in a consistent way. Sometimes it works and sometimes it does not.

No handler found for path?

Almost there - just another tiny problem: Helidon seems to ignore all resources and dutifully reports this when I try to send something to my expected resource:

No handler found for path: /todo

This was kind of tough to fix, my code looked pretty similar to the examples that I have found and that I could generate with the archetypes.

Although the examples just included helidon-dependencies, I also had to include helidon-bom to get this working:



After all the problems with Helidon it is a weird surprise, that there is no currently usable support of MicroStream right now. Still - sticking to the original plan, let es see what it is all about. Citation time:

Realize ultra-fast in-memory data processing with pure Java. Microsecond query time. Low-latency data access. Gigantic data throughput and workloads. Save lots of CPU power, CO2 emission, and costs in the data center.

Between all of this marketing blabla, there are still some interesting properties. Let me try to explain it in my own words:

MicroStream basically allows you to store and retrieve any kind of custom data at a given path. And since it basically retrieves the complete structure for you, there is no need for any kind of special query language; all basic operations, filters and so on still work.

If you want to store deep and nested data there is neat trick, lazy loading can be used here so it is just retrieved when really necessary. My current example doesn’t realy makes use of it, but the examples clearly state how this can be done and what the obvious advantage of it is.

Getting started

Getting started is really easy and since the latest release 05.00.02-MS-GA its even directly available from Maven. So since I cannot describe it any better:


So this is combined post for two things, which I thought would work nicely along each other. Unfortunately, there is still some way to go this combination.

Helidon is pretty fast and once you really fixed some the initial problems adding features is pretty straight forward. There is a huge list of extensions and I am eager to test it in a real scenario.

MicroStream is also really interesting, since you basically define the structure, the handling is pretty easy and there is no additional set up required, like for any other database. I currently don’t have any ideas how to really make use of it, but I will surely keep it in the back of my mind.

My showcase can be found here: