wtorek, 25 lipca 2017

[memo] hibernate's import.sql

There is a neat, heavily undocumented feature oh Hibernate - import.sql.

If Hibernate creates DB schema from scratch - "hibernate.hbm2ddl.auto" is set to either "create" or "create-drop", it will load "import.sql" file located in the root classpath. If Spring Boot is used, the property controlling the behaviour is "spring.jpa.hibernate.ddl-auto".

But why would anyone like to import some static data in a webapp? Well, for prototyping purposes for example. Or for "static" webapp mocking some external resources for integration testing. 

poniedziałek, 24 lipca 2017

Continuous Integration for (non)hipsters

Continuous Integration? Soooo ooold, so ninetees. Not hot anymore, not trendy. Currently even Continuous Delivery sounds like something regular, typical, borig. Everybody does CI... or do they?

In order to answer this question, let's refer to the excellent article, published by Martin Fowler here. Headline states:
Continuous Integration is a software development practice where members of a team integrate their work frequently (...). Each integration is verified by an automated build (including test) to detect integration errors as quickly as possible.
That's it.
Code (yes, this includes tests!)
Pull/push (integrate).
Let something (a CI server for instance) run tests and confirm that everything is in order

Four easy steps. However, the devil is in the detail.

First of all, the steps should be executed at least once a day, preferably multiple times a day by each team member. This way, any integration issues will be discovered on the spot. If your team has a habit of keeping private branches for a long time, without source integration and pushes (triggering a full CI build), well, you're not doing CI! If you use feature branches, which are a good thing, keep them public, so that CI server can watch them during development time.

Second of all, tests are the cornerstone of CI. Usually not all tests are run during build - in order to make it faster, only quick, small unit ones. If project build isn't fast, developers won't build before pushing changes (we're all always super busy, aren't we?). Therefore all expensive tests - especially integration ones - should be left for CI server. It's a general rule for a bigger builds. This way if an issue fits into this 1% not covered by unit tests, it should be found by the end of the day. By the way it's really a good habit to have a blame mails enabled in the CI server. The name is a bit misleading - it's not about the blame, it's all about fixing broken build (or bad tests!) as soon as possible.

All of what was above can be found in the aforementioned Martin Fowler's article - in a more elaborate way. Yes, it's a quite old one, but still very, very relevant.

czwartek, 13 lipca 2017

[memo] purging broken JARs from Maven repository

Ever encountered dreaded "java.util.zip.ZipException: invalid LOC header (bad signature)" while building a Maven project? If yes, it means that Maven (somehow) downloaded a broken JAR into your repository. There is not much that can be done besides purging all of the "broken" JARs from the repository.

Two options are possible:

  • delete whole Maven repository - which means downloading all of the JARs, of all projects (possibly few gigs) again (!!)
  • delete only offending JARs - list can be obtained for example by issuing following command:
find  /home/me/.m2/repository/ -name "*jar" | xargs -L 1 zip -T | grep error | grep invalid

 Both options, well, suck :-) Fortunately there is a way to purge all of the JARs from local repository that pertain to only one project. It's provided by the dependency Maven plugin. Just issue
mvn dependency:purge-local-repository
and it's done. NEAT!

poniedziałek, 12 czerwca 2017

Hazelcast - CLI access

Ever wondered how to quickly take a peek into your Hazelcast structures, for example on a UAT / CIT environment? Look no further! :-) I've recently had a similar task. Debugging an issue on a test environment I reckoned it might be caused by a faulty data in the Hazelcast cluster. Fortunately we can use what comes with a Java application using Hazelcast (in a client mode) - class ClientTestApp.

First of all we're going to need two Hazelcast JARs (here - version 3.2.5):

  • hazelcast-client-3.2.5.jar
  • hazelcast-3.2.5.jar

Both JARs should be copied into empty directory, let's call it "lib" for this demo purposes. Next, a shell script used to run the test app needs to be created:

In order to have the client connect with your cluster, a configuration needs to be provided as well. The file needs to be named hazelcast-client.xml and reside in the same directory as the run.sh script. Sample content looks as follows:

After running the client, you should get a Hazelcast console able to query / manage the cluster. Full manual of the CLI is here: http://docs.hazelcast.org/docs/2.3/manual/html/ch17s09.html

Enjoy querying your data! 

środa, 31 maja 2017

GeeCon part two

A little late (almost two weeks!) but finally completed. Second day of GeeCon (https://www.geecon.org/). How was it? Continue reading to find out.

Improving Java EE with reactive - Ondrej Mihalyi

The presenter started with an outlook of what "reactive" in terms of a web application really means. The idea he focused on was that in order to improve the latency, execution of a request should not block - never, even on I/O. Also, in order to utilise the resources (CPU) as efficiently as possible, there should be ideally as many threads running as there are cores in the system. In a typical, J2EE based application, there goals are impossible to achieve, as each request is served completely by a separate thread which blocks if there is eg a dependent service or a DB call. There are however libraries that can help to make such application more "reactive". In his demo application ("cargo"), Ondrej showed how to use built-in Java 8 CompletableFuture or external RxJava (https://github.com/ReactiveX/RxJava) observables in order to avoid blocking the execution thread. He also mentioned (although he was short on time) that the UI part should be improved as well by using technologies like WebSockets or CDI events.
Whole presentation was quite good content-wise. It was nice to learn how a performance can be improved in an existing application by refactoring it to use some "reactive" stuff. The presenter could improve a bit on a technical side. Keeping an eye on the clock and minimising "live coding" favouring ready, refactored examples would make whole presentation better from reception point of view.

Reactive Spring - Josh Long 

START. DOT SPRING. DOT IO. I could write that this was the second "reactive" presentation, taking on the topic from new Spring library perspective. But no, this was not an ordinary presentation. This was a show. A Josh show. The topic itseflf is very interesting and the Spring implementations are interesting (and impressive) as well. Reactive versions of repositories (Mongo DB implementation here), Reactive Streams (Subscriber, Publisher, Processor) and Reactor (Flux, Mono) concepts, Web Sockets or Server Sent Events for publishing. They even have (in the upcoming release) a reactive, non-blocking security! I had however a strong impression that Josh would be able to make an interesting and involving presentation on any topic... even PHP ;-) Besides strong interest in the Spring reactive what took out of the presentation is - START. DOT SPRING. DOT IO! :-D

Microservices - stages of maturity - Jarosław Pałka / Jakub Marchwicki

The multi-threaded presentation run on two cores in parallel ;-) It was a mixed one - a bit about the main topic (microservices), a bit about a working in a tech organisation. The microservices-oriented part dealt a bit with such principles as being event-driven (publish, publish, publish!) and asynchronous, even in terms of application logging. Also, the Customer Driven Contracts for better APIs were mentioned. The message from the presenters here was that many of the microservices world ideas can be applied to the world of monoliths. The organisation-oriented part was, from my point of view, much more interesting. Jarek and Jakub said many things that may seem obvious, but need to be stated aloud from time to time, just to remind everyone about them. Amon others, the words of wisdom I remembered from the presentation were:
- legacy products - usually nobody to work with these, but usually these are the ones that bring MONEY!
- 3rd Newtonian law of management - if you push people, they will push back even harder
- ignoring the infrastructure is a wide road to failure
- developers should be assigned responsibilities, not roles
- during development focus should be on building a resilient system, not a perfect one
- in general, it's better to fix what's failing than on blaming others (famous "witch hunt")
- never ever do any manual changes on production - if you need to, your product is crap ;-)
Overall, I liked the presentation, especially that my work experience results in similar conclusions as voiced by Jarek and Jakub.

Consumer-Driven Contracts to enable API evolution - Marcin Grzejszczak

Consumer-Driven Contracts is the pattern to enable service evolution, as described by Martin Fowler (https://martinfowler.com/articles/consumerDrivenContracts.html). In his presentation Marcin focused on how CDC can be enabled for a web application using Spring project called Spring Cloud Contract (http://cloud.spring.io/spring-cloud-contract/spring-cloud-contract.html). The idea behind is quite simple - allow writing Contract on an API using a statically typed Groovy DSL, that can be later on automagically converted into stubs used for (client) intergration testing (in a most hyped microservices architecture ;) ). As an added bonus, the same tool will generate (server) acceptance tests out of the same Contracts.
To make long story short - easier decoupling of services for testing and less boilerplate code provided by one nice tool. I like that! :-)

To sum up - this year's edition of GeeCon was both entertaining and educational. I learned few new things, I met some friends from good old days, I ate some cookies. One of the most important aspects for me was an opportunity to see how different things are done in different companies. Having a broader overview is never a bad thing!