The April meetup was sponsored by Blueground at the Impact Hub in Psyri, Athens. Apart from leasing the space, Blueground also kindly offered pizzas and beer for all the attendees.

Kostis Kapelonis on behalf of JHUG welcomed the participants with an urge. This season JHUG has many proposals from sponsors for meetups but the speakers are limited. He urged people to do talks on all topics regarding java and/or the jvm. JHUG is open to all speakers and topics and most importantly the members of JHUG throughout its lifetime — it is the oldest Greek meetup founded in 2001 — have proved that they respect every speaker regardless of the topic, the presentation skills or the content level.

After that Stratos Pavlakis VP of Engineering at Blueground presented the company, what they do and their engineering culture. It was of great interest when he described that the company started as an operations company but eventually had to evolve into a tech company to handle the increasing scale. Moreover Stratos as a co-organizer of the GreeceJS meetup added some useful thoughts on the topic addressed by Kostis before him.

The meetup then continued as always with two talks and a beer-pizza-networking break.

Testing Anti-patterns

The first talk was from Kostis Kapelonis about software testing anti-patterns. Kostis is a firm believer in that testing done right gives great value to a code base. He has given many presentations on this topic and has written a book about it.

Wikipedia defines an anti-pattern as a common response to a recurring problem that is usually ineffective and risks being highly counterproductive. So, imagine a talk that will tell 100 attendees they do testing wrong, combine it with the lively and provocative presenting style of Kostis and you get the context of the talk.

The talk was a live commentary on a revised edition of a popular blog post by Kostis. After giving an overview of how testing should be done properly he defined and explained the following list of anti-patterns.

1. Having unit tests without integration tests
2. Having integration tests without unit tests
3. Having the wrong kind of tests
4. Testing the wrong functionality
5. Testing internal implementation
6. Paying excessive attention to test coverage
7. Having flaky or slow tests
8. Running tests manually
9. Treating test code as a second class citizen
10. Not converting production bugs to tests
11. Treating TDD as a religion
12. Writing tests without reading documentation first

For each one of them, he presented the topic in detail, refuted the arguments that consider it a best practice and explained why it is an anti-pattern. In almost all of the topics there were questions from people who either did not consider it an anti-pattern or were not convinced by Kostis arguments. He answered many questions and eventually the talk went well beyond the time limit so the organizers had to end it.

The talk was very interesting, easy and enjoyable to follow and thought provoking as expected, and promised, by Kostis. The video will go live soon on our vimeo channel and it is highly recommended. The original blog post is also worth reading. The topic of course is very large and cannot finish in one talk. As a closing note we repeat some of the general advices Kostis gave for proper testing.

• Automate, automate, automate
• A developer must be able to run the whole test suite easily, fast and out of the box for every new code base he is involved.
• If tests do not give value to business they are useless even if they are correct and well written.
• When in doubt what to test, monitor the state of production

Introduction to Quarkus

The second talk was about Quarkus a new, very promising framework from Red Hat. The project is very new, released about a month ago so this talk was a JHUG exclusivity. Moreover, the speaker Georgios Andrianakis is a contributor to the project so he has a very good understanding of the design tradeoffs used for quarkus.

He started the talk by setting the context for quarkus, why a new framework was needed and where it stands in the java ecosystem. The problems it addresses are with java in production and mostly with cloud deployments. In such environments characteristics of java like large memory footprints, slow startup times, class loading issues etc are drawbacks and hinter the adoption of java. These are relics of the era where java was used in inhouse clusters and the application servers took full control of the machines. He pointed out that production environments are dynamic in essence, configuration changes, code changes, dependencies changes, and thus a new more flexible way was needed to address these issues.

Then he described Quarkus which is composed of 2 things.

First, a java stack for development that includes well established frameworks like hibernate, Resteasy, eclipse microprofile, netty, kafka, vert.x (enter reactive) and many more are on the way. All these are used by java developers daily and thus if you adopt quarkus you are not forced to learn something new but you can continue to use the things you know and trust.

Second, a runtime environment based on GraalVM which powerups your application and gives you smaller memory footprint, very fast startup times, live reloading of code and configuration and if you choose, a native executable. Note that quarkus applications can still run on the JVM if you choose but in this case you lose many of quarkus benefits.

Of course as you understand quarkus is much more than assembling a jar from the above frameworks and running it on GraalVM. It does some hard work both during the build time and during the runtime to ensure that you get the benefits of the platform. During build time it does static code analysis to eliminate dead code, remove unused classes, reduce reflection calls, all of which reduce the memory footprint and fasten application startup. During runtime it does not do aggressive classloading or reflection or dynamic proxied or use agents like JMX as this incurs additional costs that are maybe insignificant for in house deployments but are very expensive for cloud deployments. In a nutshell you must write code the quarkus way. If you use the supported frameworks it is very easy and straightforward. If you don’t then you must either wait till they are supported or do some good code reviews to make your app quarkus ready.

After the presentation Giorgos gave a live demo that demonstrated build times, startup times, live reloading, native executables and finally support of jpa. It was a very good demo as he was very confident in quarkus and was eager to ask the audience “what do you want to run next?”

The Q&A session was about quarkus support, mostly how well it supports spring, a framework that heavily relies on reflection and dynamic proxies and how ready is quarkus for production. Giorgos suggested adoption of quarkus, it is very mature, not production ready yet but it is actively developed and it will be ready for production soon. As for spring support it is improving, some of its parts work fine, but the full framework is not quarkus ready yet.

That was an excellent talk and helped us get a clear view of quarkus beyond the buzzwords. Those that missed it should definitely see the video of the talk when we release it in our vimeo channel. Also Giorgos will give another talk for quarkus at the May Kubernetes meetup

Aftermath

Of course besides the talks there was a lot of networking between our members, old and new, and a lot of ideas exchanged. The positive energy that such meetups give to the attendants is enormous.

In this meet up we also made a draw for two IntelliJ licenses a gentle offer of Jetbrains and two tickets for Voxxed Days Athens a gentle offer of SoftConf. They are both firm supporters of JHUG and we thank them a lot.

Join JHUG

You can learn news about JHUG, participate and exchange ideas and feedback via our channels:

• Slack
• Twitter
• Meetup
• Blog
• Vimeo

News about meetups and other events are published in all these channels but the interesting discussions are on slack. If you are not there, consider joining.

See you at the next meetup. Until then keep coding.

The last meetup for 2018 (meetup.com) was sponsored by Intralot at the Impact Hub in Psyri. Apart from leasing the space, Intralot also kindly offered pizzas and beer for all the attendees.

A little more than 100 people attended the meetup, many new faces among them. For those who couldn’t attend, we recorded the meetup, so either revisit this post for the videos, or subscribe to our Vimeo channel.

The meetup kicked off with Thomas Pliakas, from the JHUG team, who welcomed the attendants on behalf of the group. As Thomas stressed, JHUG exists thanks to people who volunteer to present, so if there is something you like and use and want to share your passion about it, submit a presentation proposal to our call-for-presentations form. Also, we have an active Slack channel, check the instructions in the box on the right side of this post to get an invitation.

Afterwards, Irene Dimou took the stage and presented what our host, Intralot, works on, how it is organised, and how much it has grown over the years, now employing over 700 people in Greece and many more worldwide. With the economy crisis still going strong, it is very consoling to see that there are – mostly IT – companies that build expertise and thrive internationally.

High performance asynchronous transaction orchestration with Java Reactive frameworks

The first presentation was by Nikos Papadopoulos and Vasilis Petropoulos, both Engineers at Intralot. They started by presenting the special requirements their business brings with it: multitude of clients, large numbers of transactions with spikes in traffic, low response times, regulations for auditing and logging, penalties for mishandled transactions, runtime configurability. A practical aspect that raised some eyebrows was that their traffic may go up several times in a matter of minutes, and then go down again. Their solution needed to scale that fast, and then scale down so as to keep the bill low. They then discussed how the Reactive Manifesto and Microservices with Docker and Kubernetes are a good fit for them.

Nikos and Vasilis then presented the toolset they chose in order to accommodate their needs:

• Netty: it’s significantly more lightweight than Tomcat, event-driven and its thread model is customizable
• Spring Boot 2 with Spring 5: A mature framework with easy DI configuration and libraries for everything, produces a single containerizable jar file
• Spring Webflux: Spring’s reactive web framework, which can sit on top of Netty, providing mechanisms for back-pressure, filtering, sorting batching etc.
• Spring Actuator: Spring’s library that provides real-time information and metrics on the status of our application
• Jersey: The popular JAX-RS implementation, which can be used to generate Swagger docs for our APIs
• jBPM: A business process modelling framework to comceptualize, design and develop service flows

Nikos and Vasilis went on to discuss the challenges they faced implementing their solution, which both technical (i.e. making all the tools work together) and non-technical (introducing a paradigm shift to the asynchronous world for their team). Their implementation, which is in production as you are reading this, met the requirements they had set initially, achieving the elasticity and resilience their clients needs.

A final point we spent some time discussing was the way they are achieving eventual consistency in the distributed world. For each flow, they maintaining a reverse one that reverts it. When kicking off complex operations, they are keeping a log of the list of sub-operations (flows) that need to take place, and if one of them fails, they execute the reverse flows for all executed flows. Although they didn’t use the word, this sounds like the Saga pattern.

You can find the presentation here

Java puzzlers

George Kalfopoulos from Trasys (now part of NRB) prepared 10-minute Java puzzlers session. After some head-scratching and facepalms, the quickest answers won two books we gave away. This small session was so engaging we are very keen to repeating it in the near future.

JUnit 5

The second talk was by our own Thomas Pliakas on JUnit 5. Thomas took the risk and did a live-coding session, fortunately everything worked out.

Thomas started by presenting how JUnit is organised at a high level, supporting both new tests (Jupiter) and old JUnit 4 tests (Vintage).

He went on with the new annotations. Some of them are just a rename of corresponding JUnit 4 annotations. Some others though, are new, for example the @DisplayName annotation that can be used to give a human-readable name to a test method, different than the one infered from the method name. Similarly, JUnit 5 comes with its own list of Assumptions (“lesser” assertions).

An important addition is the Conditional Test Execution. Apart from the baked-in list of conditions (i.e. running only on Linux, or on Java 11, or if environment variable FOO is set to BAR), one can write their own conditions.

Another feature is Tags. By tagging tests, you can run specific subsets of your tests.

Other (seemingly less important) features exist, such as nested tests, test interfaces and default methods. We didn’t see much value in them when discussing them, but you may. Let us know if you do.

Finally, JUnit 5 comes with first class support for repeated and parameterized tests, as well as parallel test execution, which promises to make our builds faster.

For additional resources, you can check the sample JUnit 5 projects on Github, as well as Thomas’ junit repository.

Το Χριστουγεννιάτικο meetup μας θα γίνει τη Δευτέρα 3 Δεκεμβρίου στο Impact Hub στου Ψυρρή. Το event θα κάνει host η Intralot.

RSVP και περισσότερα εδώ.

It was a rainy and windy day (September 27th 2018) when JHUG started the meetups for the new season 2018/2019. We, the organizers of JHUG, were a bit anxious whether people will attend. It was the first meetup and the weather was bad. However it was an excellent start. Java apps may suffer sometimes from slow booting but Java meetups do not have such problems. We estimated that about 100 people, most of them newcomers, attended the meetup. This is very encouraging and sets a high bar we will try to cross.

The meetup was held in the premises of The Hub Events and was sponsored by Accenture. Markos Fragkakis welcomed the attendants on behalf of JHUG and wished for a good season with a lot of Java. He then passed the word to Nicolas Moschatos the HR Manager of Accenture. He welcomed the JHUG members and stated Accenture’s satisfaction and commitment to Java technology, their support for JHUG and their pursuit to collaborate with talented engineers. A team of HR stuff and engineers were active during the meetup discussing career opportunities with the attendants.

After the introductions the talks started.

An overview of IntelliJ IDEA – Zisis Pontikas – Slides

Zisis chose to talk about the latest version of the best and most popular IDE for JVM based platforms. He did a quick chronology of IDEA and the milestones of its development. Then we proceed to do live demos including

• project organization
• build tools integration
• git integration
• code refactoring
• code test and coverage
• spring boot integration
• live templates

It was a big task for the 45 minutes but he did fine. New users were surely challenged to have a look at IDEA while old user learned some new tricks and felt justified for the time they devoted to learn the tool. You can watch the full video below.

Break

After the talk there was the essential break for food, beer and networking in no particular order of significance. This time is was very important because the newcomers were many and a lot of acquaintances were made. Also there was a lot of ideas and suggestions for future meetups. During this break there was also a draw for 2 IDEA ultimate licenses offered by JetBrains.

Microservices architecture in action – Giannis Kormaris – Slides

The second talk by Yannis was about software architecture. Microservices are trending these days but still there isn’t an acceptable definition of what constitutes a microservices architecture. This talk contributed to the ongoing dialogue. Yannis presented a general overview of what is such an architecture and when applicable he become very specific with concrete examples from projects he had worked on. It was very valuable that all examples were from personal experience and that was justified in the Q&A section(more later). The topics addressed were:

• monolith vs microservices
• complex business domain
• services API
• business capabilities
• scalability
• error handling
• distribution of services
• deployment

and much more.

Technology wise he showed a bias towards RabbitMQ and OpenShift, which he called Kubernetes on steroids, and he discussed a bit about their technical merits.

This talk concluded with a good Q&A section in which proponents of monolithic apps and monolithic packaging argued about code structure, distributed transactions, performance penalties, easiness of testing etc. Surely, if the time hadn’t passed we would have stayed and talked about these the whole night. You can watch the full video below.

The hidden talk

Yannis mentioned in his talk that he attendend a JHUG meetup some years ago and was inspired by a talk by Kostis Kapelonis Package By Feature. He considered the organization proposed there a good template for organizing code for a microservice. You can find the original talk at JHUG 2010, along with a revised version of it at Oracle Java Day 2014 here

.next()

To conclude it was a very interesting meetup and a very promising start. We are looking forward to worthy followups. All talks were recorded in video and will be released soon for those who weren’t able to attent. At the meetup page, here, there is a photo gallery from the meetup.

.join()

You can learn news about JHUG, participate and exchange ideas and feedback via our channels:

• Slack
• Twitter
• Meetup
• Blog

News about meetups and other events are published in all these channels but the interesting discussions are on slack. If you are not there, consider joining.

See you at the next meetup. Until then keep coding.

This post was written by Spyros Anastasopoulos

The first JHUG meetup for 2018 was held at the premises of Advantage FSE. Ms Peggy Theodorou-Zoumi on behalf of Advantage FSE, welcomed the members of JHUG at their premises for yet another more time as they are fond supporters of our group and they too believe that people are the most important value in our industry.

After this warm welcome the organizers Thomas and Spyros took the word to motivate members to give talks for the forthcoming events. Since both of them are experienced engineers there was a clear separation of concerns in their calls and one asked for subjects while the other for speakers.

Thomas

I want you to speak about subjects you don’t know anything about but you find interesting and you are curious. Do some research, experiment a bit and come to give a talk. I am sure it will be very good.

Spyros

Our community is growing and there are many new faces in each meetup. The best way to get to know each other is a lightning talk. Come up and tell us who you are, what you are working on, what you have to tell and what you want to hear. A lightning talk for 10 minutes on any topic is very easy to do and will help to evolve and grow the community even more.

There is a form to declare your interest in giving a talk and we urge you to submit a proposal. Remember that the most important thing for a talk in communities like ours it to create traction and empathy. The value of the talk is important but secondary.

And now the major part, the talks.

The first speaker was Antonis Lilis of Advantage FSE. He is a regular member of JHUG and has given us very interesting talks on mobile computing. For this meetup he chose to talk about

A short introduction to the Kotlin language for Java Developers

Kotlin is a language for the JVM developed by JetBrains. It was released as open source in 2012 and there was a major interest in it when Google announced it as a language for Android development in 2017.

The talk was targeted to programmers familiar with Java. Antonis presented in a concise, sweet and up to the point way the features of Kotlin that make it both attractive and productive. It is not an academic language or an experiment, it is designed for modern applications.

It runs on the JVM but it is not an extension or an upgrade to Java. Familiarity with Java helps a lot to reduce the learning curve but it is not a prerequisite.

Kotlin is a statically typed language that supports both object-oriented and functional paradigms. It has first class functions, type inference, some nice syntactic shortcuts like null check operators, safe casting, companion objects and many more structures that look natural in Kotlin but compared with Java they greatly reduce boilerplate code. Kotlin also supports composition instead of inheritance as the primary mechanism for extending classes and has data classes which in essence are value classes generated by the compiler. It has also a proposal for structure concurrency in coroutines which you can think of as very lightweight threads. The slides are very descriptive and you can start programming in Kotlin just be reading them.

It is supported by all major IDEs. The toolchain for it is quite stable and keeps improving as the language gains interest.

At the end Antonis answered questions about the stability and the future of the language.

In my opinion Kotlin is another language for the JVM like scala, groovy, clojure and it has to answer the same question: It certainly makes programs easier to write but are there any safeguards to preserve the readability? We have seen examples of scala and groovy where programs become completely unreadable because of feature abuse and not forget that one of the advantages of Java is that it has the same readability/writeability ratio. The advantage for Kotlin is that is has a very suitable environment for it as it is a first citizen language for Android and the characteristics of mobile apps favor such high level languages.

Kotlin is definitely a project to track and this talk by Antonis did a great job to promote it.

Pizza, Beers and Networking

This is one of the best parts of every meetup. A break during the two talks for pizza and beers kindly offered by our host Advantage FSE. There was a full round of networking to meet other JHUG members and talk about interesting debugging stories, production failures, upcoming technologies, vim vs emacs etc For this meetup the topic was Kotlin and how Java/Scala/Ruby/Awk does a better job 🙂

Istio – Service mesh

The second talk was delivered by Georgios Andrianakis of RedHat. He chose to present Istio a new and trending technology which most attendees were not acquainted with. The talk was intended for newcomers and it was also a tutorial for service meshes in general.

Georgios started describing microservices architectures and how their essence, that no matter how you design them they are a distributed system and underneath them there is an unreliable network, is the cause of most problems. He then presented and analyzed the major architectural challenges regarding distributed systems like resilience, fault tolerance, load balancing, canary deployments and discussed potential solutions. It seems there are two approaches:

The old one was to use state of the art code libraries like hystrix, zuul, zipkin and embed reliability in the application. That proved inadequate for medium to large installations as code maintenance costs became intolerable even for large organizations.

The modern approach is to develop a _platform_ in which you deploy your microservices and the platform takes care of all the architectural challenges and production issues. An important step towards that direction was Kubernetes which to oversimplify manages your cluster and provides a platform that handles discovery, invocation, elasticity and monitoring. Thaw was important but not enough. The next step is the *service mesh* which in Georgios words is

a decentralized, application networking infrastructure between your services that provides resilience, security, observability and routing control

Then he proceeded to present Istio, its architecture and a typical setup. To demonstrate the benefits he presented a setup with 2 services talking to each other and analyzed the whole request/response cycle between them and how Kubernetes and Istio combined _tame_ the network.

The slides are excellent and repay study. You can find them here.

That was an excellent talk and this what JHUG is about. A good talk on a promising technology that inspires you to explore it and who knows maybe prepare a new talk for it for a next meetup (suggestion: do it!).

Closing

After the talks there was a draw for one copy of Kotlin in Action and we updated our meetup for the beginning of April. Stay tuned for the details at meetup, twitter and slack.

Το meetup του Φεβρουαρίου θα φιλοξενήσει η Advantage FSE.

Οι ομιλίες:

A short introduction to the Kotlin language for Java Developers – Antonis Lilis [1]

Do you like Java but wish you didn’t have to write so much boilerplate code? Kotlin aims to address many of the pitfalls that are common with Java development, while making your code more concise, safe, and expressive. It is also 100% interoperable with Java and can be mixed in the same project.

Introduction to Istio Service Mesh – Georgios Andrianakis [2]

The purpose of the presentation is an introduction to the Istio project. We will explore what it can offer to those who want to develop Microservices.

Ενδεικτικό πρόγραμμα

• 18.30 – Προσέλευση/ έλεγχος εισόδου

• 19.00 – 19.15 Παρουσίαση χορηγου

• 19.15 – 20.15 – Ομιλία για Kotlin

• 20.15 – 20.30 Πίτσα/μπυρα/πηγαδάκια/networking

• 20.30 – 21.30 Ομιλία για Istio

Κρατάτε μαζί σας την ταυτότητα σας για λόγους ασφαλείας στην εισοδο.

Σας περιμένουμε!

(Είσοδος ελευθερη)

[1] http://www.linkedin.com/in/alilis
[2] https://www.linkedin.com/in/georgios-andrianakis-71305815

Το επόμενο meetup θα φιλοξενήσει η Eurobank στις 28 Νοεμβρίου. RSVP εδώ.

Για τη γενική τοποθεσία μπορείτε να δείτε το χάρτη. Το meetup θα γίνει στο Κτίριο Η / συνεδριακό κέντρο. Μόλις έχουμε αναλυτικές οδηγίες για το πώς μπορείτε να έρθετε, θα τις αναρτήσουμε.

Οι ομιλίες:

Using JCache to speed up your apps – Vassilis Bekiaris (Linkedin)

JCache (JSR-107) is the standardized way to temporarily cache data in your Java apps. In this talk, we will explore basic caching concepts, introduce the JCache API and go through sample caching use cases covering basic usage and integration scenarios.

Going to production with Docker, Kubernetes and Java microservices – Anestis Georgiadis (Linkedin)

An overview of the journey to production for a system being built from the bottom up as cloud-native. We will be presenting architectural choices for the Java stack, development tooling based on Docker, the value of Kubernetes and things to consider overall before embarking on a similar journey.

Ενδεικτικό πρόγραμμα

• 18.30 – Προσέλευση/ έλεγχος εισόδου

• 19.00 – 19.15 Παρουσίαση χορηγου

• 19.15 – 20.15 – Ομιλία για JCache

• 20.15 – 20.30 Πίτσα/μπυρα/πηγαδάκια/networking

• 20.30 – 21.30 Ομιλία για Docker, Kubernetes και Java Microservices

Κρατάτε μαζί σας την ταυτότητα σας για λόγους ασφαλείας στην εισοδο.

Σας περιμένουμε!

(Είσοδος ελευθερη)