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)

Java Hellenic User Group | Η ελληνική κοινότητα προγραμματιστών Java

Παρουσιαση 1 – Refactoring in Practice

• Παναγιώτης Καπράλος: https://www.linkedin.com/in/panagiotis-kapralos-84b0078b
• Βιντεο: https://vimeo.com/208950085
• Διαφάνειες: https://github.com/JHUG/JHUG-General-Resources/blob/master/presentations/2017/03-March/Refactoring-In-Practice.pdf

Παρουσιαση 2 – Microbenchmarking with JMH

• Γιώργος Καλφόπουλος:
• Βίντεο: https://vimeo.com/208947227
• Διαφάνειες: https://github.com/JHUG/JHUG-General-Resources/blob/master/presentations/2017/03-March/Microbenchmarking.pdf

Περιμένουμε τις δικές σας ιδέες για παρουσιάσεις. Οποιοδήποτε θεμα
εχει σχεση με Java και σας ενδιαφέρει μπορεί να γίνει παρουσίαση. Δεν
είναι ανάγκη να ειναι κατι προχωρημένο, αρκεί να σας αρέσει.

Κάντε την προταση σας ειτε στο https://www.meetup.com/Java-Hellenic-User-Group/ είτε στην λίστα https://groups.google.com/forum/?fromgroups#!forum/jhug

Ραντεβου στην επόμενη συνάντηση!