DDevelopment & Design

Friends with benefits

Back when I was at my first university, working on my B.Sc., it was obvious for us, students, to always try to get into any possible, open IT event in the town. We were hungry for knowledge, for experience, anxious looking at the future. One of the really bad professors out there, told us on the first lecture, that whatever we learn is going to be outdated the moment we learn it. He said that we won’t be able to keep up the pace, that we will burn out, we will be replaced by some newfags before we even learn to do the job. And there is no hope for us.

It wasn’t a good university, it was a young one. A young university in a small town, with very old professors. Some of those guys were there, because no one else would take them. So yeah, we were anxious. Anxious that we are not getting any good education, anxious we will not find a good job afterwards, anxious we will become burned out before we know it.

But we were also very young, young enough to believe, we won’t be giving it up without a fight. And thus we were learning on our own, reading books, coding, getting together and sharing what little knowledge we had. And we applied for every interesting position around, to get as much experience as we could.

Not that we had many options. As I said, it was a small town.

After B.Sc., I moved to Warsaw. Started my M.Sc. at another university, which turned out to be no better, but it didn’t matter anymore. I had a good job as a programmer, with fantastic, smart people. In half a year, I learned more, than in five years at all the universities.

Then I moved to another company. Changed the technology stack completely. Started anew, and had great time learning from all those smart people around me, and teaching them whatever I could.

And there was not a single event I would attend to, or hear anybody do it. It seemed like a thing of the past. We had so much knowledge to learn inside the company, why move, why go anywhere at all?

And then I switched my technology stack again. I joined TouK. This time, however, it seemed like I could spread a lot more knowledge about TDD, OOP and good practices, than before. But to do that, I had to fill the holes in my knowledge really fast. So I got myself some books, some RSS’es, some tutorials. One day, my boss sent us an invitation for a Warsaw Java User Group meeting. Some guys were coming. I signed up to the mailing group, and off I went.

There I was, back at the University, getting to know other hairy guys at WJUG meetings, learning about their craft, their interests, and their passions. Encouraged by someone, I went to a conference. Then another. I started attending conferences on regular basis. Actually, I started attending all the Java conferences in Poland. And there are quite a few, I tell you.

Something strange happened. Apart from the technologies, personal experiences, tricks and traps, I learned something completely different. I knew I was getting tired by everyday work, that my energy was much higher after right after holidays, and I’d be much less efficient just before one. I knew I could find myself burned out, one day. I heard a story here and there, in the kitchen, over the coffee table. Someone with a sad look would mention, he has no fun anymore. The job became tiresome. Someone would talk about buying a farm. Or a workshop. Getting out of this line of work.

But at those WJUG meetings, at those conferences, my energy was replenished. The enthusiasm and passion for cool technology, hanging right out in the air, would be contagious. The people, with eyes burning bright for great things they could learn and bring back home… I could feel their hunger for knowledge. And I was back, to my student years again, feeling everything is possible. Not anxious about my future this time.

That was great.

I wanted to help those, who make it happen. To somehow thank them. And I could do that in two ways: either by helping organize, or by sharing what I knew. I prepared a small presentation about Craftsmanship for WJUG, and got a positive feedback. Then I had another, about Spring Security, and another, and so on. Then I answered a call for papers, and got myself speaking at conferences. And it was great too. I joined another great group, Agile Warsaw. I even organized a weekly workshop, here at TouK, to get all the shy people to share, and learn how good it feels.

I have to confess, though. Speaking at conferences is a terrible strain for an anti-social, hairy guy like me. There is so much stress involved. If I wanted to be in spotlights, I wouldn’t become a programmer in the first place. No one digs inside computers, because of love for humanity, I suppose.

Local group meetings, like WJUG, are a completely different story, however. Those are semi-formal, with 50-150 people in an old University assembly hall, with half of them hairy sociopaths in Amiga Forever T-shirts or alike, with beards that would make Richards Stallman proud, swearing like Linus Torvalds when he was thanking Nvidia, and making jokes that would fit right into bash.org, xkcd or the Jargon File. It feels good to be around them. It feels at home.

This is as close to demoscene-kind-of-feeling, as my old ass gets. Preparing a talk for them, apart from motivating me to dig the subject thoroughly, is even better.

One of the unforeseen consequences of getting out to conferences and meetings, is that you get a lot of cool gadgets. A hat from oracle, a ninja coder from Amazon, an energy drink from Microsoft with Linux/PHP/Ruby all over it, a nerd pistol, tons of T-shirts. I didn’t have to buy a T-shirt for years. Sometimes, you even get a licence or a ticket.

Thanks to WJUG, I have the IntelliJ Idea and JProfiler, both of which are extremely good and handy pieces of software.

And yesterday… well yesterday, I got a ticket for Devoxx in Belgium, saving me a few hundred Euros.

So in case you didn’t already, get your lazy ass out, and join a local technology group, go to conferences, write a blog, share with people. You’ll be surprised by the unforeseen benefits.

Even if you are a hairy sociopath, like me.

Solution Architect @ TouK

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Inconsistent Dependency Injection to domains with Grails

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This article shows clean, non hacky way of configuring featureful event listeners for Grails application servlet context. Feat. HttpSessionListener as a Spring bean example with session timeout depending on whether user account is premium or not.

Common approaches

Speaking of session timeout config in Grails, a default approach is to install templates with a command. This way we got direct access to web.xml file. Also more unnecessary files are created. Despite that unnecessary files are unnecessary, we should also remember some other common knowledge: XML is not for humans.

Another, a bit more hacky, way is to create mysterious scripts/_Events.groovy file. Inside of which, by using not less enigmatic closure: eventWebXmlEnd = { filename -> ... }, we can parse and hack into web.xml with a help of XmlSlurper.
Even though lot of Grails plugins do it similar way, still it’s not really straightforward, is it? Besides, where’s the IDE support? Hello!?

Examples of both above ways can be seen on StackOverflow.

Simpler and cleaner way

By adding just a single line to the already generated init closure we have it done:
class BootStrap {


    def init = { servletContext ->    

        servletContext.addListener(OurListenerClass)    

    }    

}

Allrighty, this is enough to avoid XML. Sweets are served after the main course though :)

Listener as a Spring bean

Let us assume we have a requirement. Set a longer session timeout for premium user account.
Users are authenticated upon session creation through SSO.

To easy meet the requirements just instantiate the CustomTimeoutSessionListener as Spring bean at resources.groovy. We also going to need some source of the user custom session timeout. Let say a ConfigService.
beans = {    

    customTimeoutSessionListener(CustomTimeoutSessionListener) {    

        configService = ref('configService')    

    }    

}

With such approach BootStrap.groovy has to by slightly modified. To keep control on listener instantation, instead of passing listener class type, Spring bean is injected by Grails and the instance passed:
class BootStrap {


    def customTimeoutSessionListener


    def init = { servletContext ->    

        servletContext.addListener(customTimeoutSessionListener)

    }    

}

An example CustomTimeoutSessionListener implementation can look like:
import javax.servlet.http.HttpSessionEvent    

import javax.servlet.http.HttpSessionListener    

import your.app.ConfigService    


class CustomTimeoutSessionListener implements HttpSessionListener {    


    ConfigService configService


    @Override    

    void sessionCreated(HttpSessionEvent httpSessionEvent) {    

        httpSessionEvent.session.maxInactiveInterval = configService.sessionTimeoutSeconds

    }    


    @Override    

    void sessionDestroyed(HttpSessionEvent httpSessionEvent) { /* nothing to implement */ }    

}
Having at hand all power of the Spring IoC this is surely a good place to load some persisted user’s account stuff into the session or to notify any other adequate bean about user presence.

Wait, what about the user context?

Honest answer is: that depends on your case. Yet here’s an example of getSessionTimeoutMinutes() implementation using Spring Security:
import org.springframework.security.core.context.SecurityContextHolder    


class ConfigService {


    static final int 3H = 3 * 60 * 60

    static final int QUARTER = 15 * 60


    int getSessionTimeoutSeconds() {    


        String username = SecurityContextHolder.context?.authentication?.principal    

        def account = Account.findByUsername(username)    


        return account?.premium ? 3H : QUARTER

    }    

}
This example is simplified. Does not contain much of defensive programming. Just an assumption that principal is already set and is a String - unique username. Thanks to Grails convention our ConfigService is transactional so the Account domain class can use GORM dynamic finder.
OK, config fetching implementation details are out of scope here anyway. You can get, load, fetch, obtain from wherever you like to. Domain persistence, principal object, role config, external file and so on...

Any gotchas?

There is one. When running grails test command, servletContext comes as some mocked class instance without addListener method. Thus we going to have a MissingMethodException when running tests :(

Solution is typical:
def init = { servletContext ->

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        servletContext.addListener(customTimeoutSessionListener)    

    }    

}
An unnecessary obstacle if you ask me. Should I submit a Jira issue about that?

TL;DR

Just implement a HttpSessionListener. Create a Spring bean of the listener. Inject it into BootStrap.groovy and call servletContext.addListener(injectedListener).