DDevelopment & Design

Geecon 2011 – day 2

And now for part 2 of my visit to Geecon 2011!

1. Jim Webber “Revisiting SOA for the 21st century”

Now this was awesome! Jim Webber, a former ThoughtWorks employee, now Neo4j evangelist (in Neotechnology) described his views on how SOA should look – according to him. This was presented previously, on other occasions as his “Guerilla SOA” talk – generally he advocated for REST based services, loose contracts (stating that WSDLs are too verbose and code generation is evil).

Jim mentioned Martin Fowler’s article on integration databases but I couldn’t find it anywhere – thou the topic looks interesting. He also recommended BDD and exposing tests on the web for the end user to use them as early as possible.

One big point he made his case with was not relying on enterprise software. Simple tools can do much better job. He compared implementing Web Services security (Secured SOAP over HTTP over TCP IP) to REST based service accessed through HTTPS – basic and easily testable with tools like curl.

Great talk. One of the best!

2. Staffan Noteberg “Regex – the future programming”

I must confess, that this did not go too well. The whole talk was well prepared and laid out but it lacked depth. It was pretty basic introduction to regex. From the presentation’s subject I was rather prepared for some novel uses of regex – like for example: showing how to filter big volume of data with simple regex or sth.

But the talk was fun, Staffan is a good speaker. He is also an author of pomodoro technique book – I intend to read sth abut this technique and this may be a nice start

3. Bartosz Kowalewski “Is OSGI ready for wide adoption?”

If it comes to titles I tend to rely on them pretty heavily, however strange it may seem. This time I also did – and the whole talk did not give me a definitive answer to the stated question.

Sure, the presentation was informative, but it described some OSGI specific, quite low level stuff. Of course, if you want to use OSGI – even by leveraging application server with OSGI under the hood – you should know a fair bit about the technology itself. Even thou the AS does a good job of hiding OSGI container specifics from the developer, in case of problems it’s better to be well informed. All in all – the talk gave too little information for me.

4. Vaclav Pech “Pick low hanging fruit”

“Parallelism is not hard, multithreading is” – this was the key sentence of the presentation. The speaker showed how to introduce concurrency into normal java/groovy code by sprinkling it with concurrency powder. Easy enough! With GPars library he showed:

  • running processing tasks with thread pools
  • testing concurrent code
  • Fork/join Thread Pool – multiple thread queues (note to self: fork/join is good for hierarchical problems)
  • low-hanging fruits:
    • async calculations
    • fork/join
    • dataflow
    • parallel collection processing
  • Actors are great – use GPars or Akka, is sufficient to use @ActiveMethod and @ActiveObject annotations and Actors are usable in OO-world

Good talk, well received!

5. Anton Arhipov “Bytecode for discriminating developers”

Technical introduction to the world of bytecode, jvm specification details. I’ve drifted away to some other topics – really – can’t recall what this was all about.

6. Andreas Almiray “Polyglot Programming”

This was a nice talk covering Groovy, Scala and Closure. The whole point of it was to show how cool it is to play with emerging JVM languages. They are not only fun but also useful. What’s more, they bring freshness to java world, injecting it with some new paradigms and methodologies. It is easier to incorporate new ideas into younger JVM languages than to the mature Java.

7. Jim Webber “A pragmatic introduction to Neo4j”

And Jim Webber again, this time with some Neo4j evangelism. First came some taxonomy information on NoSQL databases (Not Only SQL) as a whole – than some specific examples of problems solvable with graph databases – and Neo4j is a graph database.

Main points of Jim’s talk were:

  • sharding a database is important for scalability
  • series data – should be OK to use Neo4j as their storage

Conclusion

These were all the sessions I attended. On Saturday there was a Hacker-garden, but neither I had time nor will to stay – the topics were very interesting and I’d definitely like to experience such an event, but after 2 days of continuous talks I was rather tired.

To sum up, 2011’s Geecon was a great experience, with lots of interesting talks and lots of new inspirations. Keep up the good work guys!

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DDevelopment & Design

Log4j and MDC in Grails

Log4j provides very useful feature: MDC - mapped diagnostic context. It can be used to store data in context of current thread. It may sound scary a bit but idea is simple.

My post is based on post http://burtbeckwith.com/blog/?p=521 from Burt Beckwith's excellent blog, it's definitely worth checking if you are interested in Grails.

Short background story...


Suppose we want to do logging our brand new shopping system and we want to have in each log customer's shopping basket number. And our system can be used at once by many users who can perform many transactions, actions like adding items and so on. How can we achieve that? Of course we can add basket number in every place where we do some logging but this task would be boring and error-prone. 

Instead of this we can use MDC to store variable with basket number in map. 

In fact MDC can be treated as map of custom values for current thread that can be used by logger. 


How to do that with Grails?


Using MDC with Grails is quite simple. All we need to do is to create our own custom filter which works for given urls and puts our data in MDC.

Filters in Grails are classes in directory grails-app/conf/* which names end with *Filters.groovy postfix. We can create this class manually or use Grails command: 
grails create-filters info.rnowak.App.Basket

In result class named BasketFilters will be created in grails-app/conf/info/rnowak/UberApp.

Initially filter class looks a little bit empty:
class BasketFilters {
    def filters = {
        all(controller:'*', action:'*') {
            before = {

            }
            after = { Map model ->

            }
            afterView = { Exception e ->

            }
        }
    }
}
All we need to do is fill empty closures, modify filter properties and put some data into MDC.

all is the general name of our filter, as class BasketFilters (plural!) can contain many various filters. You can name it whatever you want, for this post let assume it will be named basketFilter. 

Another thing is change of filter parameters. According to official documentation (link) we can customize our filter in many ways. You can specify controller to be filtered, its actions, filtered urls and so on. In our example you can stay with default option where filter is applied to every action of every controller. If you are interested in filtering only some urls, use uri parameter with expression describing desired urls to be filtered.

Three closures that are already defined in template have their function and they are started in these conditions:

  • before - as name says, it is executed before filtered action takes place
  • after - similarly, it is called after the action
  • afterView - called after rendering of the actions view
Ok, so now we know what are these mysterious methods and when they are called. But what can be done within them? In official Grails docs (link again) under section 7.6.3 there is a list of properties that are available to use in filter.

With that knowledge, we can proceed to implementing filter.

Putting something into MDC in filter


What we want to do is quite easy: we want to retrieve basket number from parameters and put it into MDC in our filter:
class BasketFilters {
    def filters = {
        basketFilter(controller:'*', action:'*') {
            before = {
                MDC.put("basketNumber", params.basketNumber ?: "")
            }
            after = { Map model ->
                MDC.remove("basketNumber")
            }
        }
    }
}

We retrieve basket number from Grails params map and then we put in map under specified key ("basketNumber" in this case), which will be later used in logger conversion pattern. It is important to remove custom value after processing of action to avoid leaks.

So we are putting something into MDC. But how make use of it in logs?


We can refer to custom data in MDC in conversion patter using syntax: %X{key}, where key is our key we used in filter to put data, like:
def conversionPattern = "%d{yyyy-MM-dd HH:mm:ss} %-5p %t [%c{1}] %X{basketNumber} - %m%n"


And that's it :) We've put custom data in log4j MDC and successfully used it in logs to display interesting values.