Category Archives: Allgemein

Implementation of a complex Java Iterator

In a lot of situations it is better to handle data as streams to keep the memory profile low and to decrease latency. To access data in such an environment, it is often useful to use iterators which collect data out of a stream and group them into objects and let the application use the stream like a collection of objects.

There are situations where it is not easy to implement a Java iterator with keeping the contract. Imagine a situation where a complex XML file is coming in via an InputStream and only a part of the XML file is to be parsed and aggregated into a dedicated Object. In this case keeping the contract is not so easy, because keeping hasNext() and next() in sync is complicated…

For this situation, I use a simple design which is implemented in PureSol Technologies’ Streaming Library:

The main advantage is the fixed implementation of hasNext() and next(), which is not to be changed anymore. Additionally, the whole logic to check for the next enty and to created if present was moved into a single method, so that there is no mismatch anymore between hasNext() and next(),

Another advantage can be that, there is also now the possibility to peek for the next entry:

Or a little bit more restrictive:


Hadoop Client in WildFly – A Difficult Marriage (Part 2)

After writing about the first impressions about Hadoop and its WildFly integration, I did some more research and work to bring Hadoop into JavaEE on WildFly in a more elegant way.

The follow-up idea after putting Hadoop into an EAR for isolation was to isolate Hadoop and HBase clients into a WildFly module. Both clients work very well in a Java SE environment, so the idea was to use these modules which are not container managed (like Java SE) to provide the functionality to be used in a container.

The resulting (so far) module.xml is:

For HBase client, the module.xml looks like this:

For the modules above, I cannot garantee the completeness of all dependencies, but for the use cases I have at hand, these modules work.

JavaEE: Arquillian Tests support Multi-WAR-EARs

Before version 1.0.2 Arquillian did not support EAR deployments which contained multiple WAR files. The issue was the selection of the WAR into which the arquillian artifacts are to be placed for testing. The trick until then was to remove all WAR files not needed and to leave only one WAR within the EAR.

Starting from version 1.0.2 Arquillian does support Multi-WAR-EAR-Deployments as described in

If you have an EAR which is used via

you can select a WAR with the following lines:

That’s it. After this selection Arquillian stops complaining about multiple WAR files within the EAR and the selected WAR is enriched and tested.