Friday, October 3, 2014

JavaOne 2014 - Tuesday

Hi all, here are my notes of the sessions I attended on Tuesday at JavaOne.

Where is my Memory
Important session about managing memory on your JVM. The speaker introduced us to the different memory regions on the JVM and gave us good advices about how to find memory leaks on your JVM.

Some of the tips we got during the session:

The less options you have at your startup script, the better!

if you want to know default options for your JVM use the following:
java -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version

Of course you always want to go with non-default sizes, but you should go with small increments of memory for your -Xmx and -XX:MaxPermSize options

An Important difference between Java 8 and prior versions of Java is that Java 8 got almost all the naked memory available and if you want to tune it, then you should reduce it

Developers do not think about memory, they don't destroy objects or freed memory because of the Garbage Collector, which is a subsystem of the JVM for reclaiming "unused" memory

There are some objects that are always alive and wont be collected by the garbage collector, which are called GC Roots

  • System classes
  • JNI references
  • Running Threads
  • Local variables or parameters
  • Native stack
  • Used monitors
  • And some others

This is how the garbage collector works:

  • Mark all GC Root as reachable
  • Mark all objects referenced from reachable object as reachable too
  • Repeat until all reachable objects are found
  • Everything else is garbage 

So, what is a Memory Leak?
Reachable objects that will never be used by your application and/or the repetitive creation of such objects. Some examples of memory leaks are:

  • Caches without look-ups and eviction
  • String.substring -> Prior to Java SE 7
  • Immortal threads
  • Unclosed IO streams

The symptoms of your memory leak are either OutOfMemoryError or the application runs too slow due to the excessive GC, but be careful since there may be false positives due to:

  • Too high allocation size 
  • Cache with the wrong size - Check the size of your cache
  • Trying to load too much data at onces - You can use lazy loading
  • Fat data structures - Inneficient datastructures to hold your data

Memory monitoring tools

  • VisualVM/Java Mission Control
  • jStat
  • GC logs - Use the following options -XX:+PrintGCDetails -XX:PrintGCTimeStamps -Xloggc:file.log -XX:+UseGCLogFileRotation -XX:Number at your startup script and then use GC log analyzers such as Fasterj or GCViewer

So you have a memory leak, then try this as first step

  • Reduce memory usage
  • Tune GC
  • Increase Xmx/PermGen

If it doesn't work, then you should try more advanced techniques such as Memory (Heap) dump to find out what consumes memory. Memory dump is a binary representation of objects graph written to a file. Have in mind that it is not an accurate representation of the memory but is good enough to find memory leaks.

In order to get a memory dump you can use one of the following:

  • jmap -dump:format=b,file=heap.hprof
  • Add this options to your startup script:
    -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=./java_pid<pid>.hprof

The tool used to analyze the Memory Dump is Eclipse Memory Analyzer and you should look for objects with the biggest retained size.

A final word from the speaker:
Do not use Profilers to find Memory Leaks!

More information about solving Memory leak can be found at:

Went to the Hackergarten again and during the time I was there I met Werner Keil one of the spec leads of JSR 363: Units of Measurement API, who walked me through the status of the JSR and point me to several documentation sources. This JSR is also available to adopt through the Adopt a JSR program.

RIA Technologies and Framework Panel
There was this excellent panel of experts in the RIA topic. They discussed about the state of art regarding to RIA technologies.

Native or HTML5 ?
There were a lot of opinions here, but at the end, most have agreed that in house development for administrative purposes should go HTML 5. But if you really need to get the best of the platform go native even if you have to do it for three different platforms. The audience were asked if we were doing native development for our mobile projects, just a few raised their hands.
An advice to promote code reuse is to develop your backend to return JSON so your native apps or HTML 5 apps con consume it.

Is JavaFX the future of client side Java?
Some have said Swing is gone, JavaFX is the present of client side Java, but, the audience were asked whether they were building desktop applications and many raised their hands. Then they were asked whether they were using JavaFx or Swing... and most of them are using Swing and are not planning to move to JavaFx... So the question remains and is not clear whether JavaFx is replacing or not Swing.

Last question was about what panelist are excited about for the next years?
Swing + HTML 5 - Andres Almiray
No Wrappers for HTML 5 apps - Max Katz
iOS SwiftKevin Nilson
Curious about what will happen on the UI market - Gerrit Grunwald
What new tools will come up for UI - Sven Reimers

Delivering Oracle ADF Projects: Modern Techniques
This session was really interesting because it was about using modern development techniques on the world of ADF. We saw how we can use plugins for quality of code in ADF. Also explored how testing ADF applications can be automatized by using the Oracle Application Testing Suite. Last but not least, we saw how we can use Maven with ADF. I am excited about this new feature since I've wanted to create a continuous integration environment with ADF for a while. I think I found what my next talk about ADF is going to be...

ODTUG Oracle Developers Meetup
Had the chance to meet ADF celebrities and other ADF developers on the Oracle Developers meetup, an event organized by ODTUG. I could see how popular ADF is becoming, more developers are now working with this technology and are excited about the new releases.

Oracle ADF Enterprise Architects Birds­of­a­Feather Meeting
This session was about architectural challenges that we face when developing with ADF. The session was more Q&A oriented. Some of the participants were Sten Vesterli, Chris Muir and Frank Nimphius. So imagine you, with some ADF questions and having these ADF masters in front of you to help you find your path... that's priceless.

At night we went to the Red Hat party, where we could hangout with Arun Gupta, Kevin Nilson and Dario Laverde. Had some drinks and food and enjoyed the end of day 3 at JavaOne! What a great day.

see ya!

Wednesday, October 1, 2014

JavaOne 2014 - Monday

Hello there, this was day two of JavaOne 2014, it was a full day of conferences, tried to attend as many as I could and with a wide range of topics:

How to build enterprise mobile apps that integrate with your Java EE backend
The talk was about Hybrid Apps and how to connect them to your Java EE app. A hybrid app is written with web technologies but runs as native app. 

The speaker explained how Apache Cordova wraps the html app, lets developers create JS libraries to access native features such as the camera and packs the app as an Android or iOS native app.
Regarding to the IDE, he showed how you can use Eclipse with JBoss Tools plugins and Eclipse thym plugin in order to create a hybrid mobile app. From Eclipse you can write your html files and test them on the Cordova browser which is integrated to Eclipse or you can use an emulator called Genymotion which is an Android emulator. One good thing about the emulator is that you can connect your Chrome developer tools to it.
Another nice feature is called LiveReload Server which lets you change your code and watch the changes immediately on the test browser (does not work with the emulator)

The speaker talked about how responsive frameworks such as bootstrap or heavy frameworks such as jquery mobile are not good enough for today's mobile apps. He introduced us to the ionic framework and talked about some of its pros: mobile only, big community and is integrated with Angular JS

Then we saw how JBoss Forge can help us in order to create our java classes and rest end points very fast and easy. The rest end points can be tested from Google Chrome using the Postman plugin. He also used Forge  to create the ionic application with a few commands on the console.

Regarding to Push notifications, we saw how the Unified PushServer, which is an Eclipse plugin it's a server to be deployed and it comes with Clients SDKs (ios, Android and Cordova), can help us on implement Push notifications for several platforms such as iOS, Android, Amazon, Firefox, etc. Without having to code them ourselves.

Here are the tools used during the presentation in order to develop the hybrid application:
Genymotion -Android emulator
ionic - Mobile only HTML 5 framework
Angular JS - HTML 5 web framework
JBoss Forge - Rapid Application Development tool for Maven and Java EE
Postman - Plugin for Google Chrome to test your rest en points
AeroGear Push - Push Notifications

There was a space at the JavaOne exhibition hall where attendees could contribute to open source projects, meet members of the JCP and hangout with other developers. There were different topics each day. On Monday, for example, during the time I was there I met Anatole Tresch the spec lead of JSR 354 - Currency and Money. A very nice person, who kindly explained me some parts of the API and how we can participate through the Adopt a JSR program.

Thinking in Functional Style
This is one session I could not attend last year, so this time I arrived early in order to make it inside the room. Venkat Subramaniam is by far one of the best speakers I have ever seen. He introduced us to functional programming with simple examples and engaged the audience with such simple stories, jokes and easy vocabulary. When he starts talking, he doesn't stop until the session is over. Highly recommend to attend to his sessions. Here are some topics about functional programming that he talked about:

  • Assignment-less programming
  • Immutable state -> Less error prone
  • Functions with no side-effect
  • Declarative - The what, transform data, pure, pass functions as parameters, functional composition
  • Function composition - You can chain functions
  • Lazy evaluations - Is good since not all evaluations are applied
  • Immutability and pure functions make functional programming

You can download the topics list and code examples from:
Thinking in functional style

JCP anniversary
At night, we were invited to the 15th anniversary of the JCP. Special thanks to Heather Vancura for such a great party at the 46th floor of the Hilton Union Square hotel. Nice view of San Francisco, food and beverage, entertainment was provided by the NullPointers, a band of Java Geeks who showed their passion for music.

Was a great day, looking forward for more fun at JavaOne.

See ya!