DDevelopment & Design

Eclipse ecosystem

Do you use Eclipse? Or perhaps you use other IDE but would like to try “the big E”? Well, that’s OK, and completely understandable, because Eclipse is actually a great, versatile tool. But Eclipse is not just an IDE, in fact it is a comp let, extensible platform. What’s even more important, there are tones of valuable Eclipse-related projects gathered around the platform.

Yes, there are lots. Some are good, some are bad, but the usual, stock ones, signed by Eclipse, are worth taking a closer look. They’re not a mere innovation to the way we write code with an IDE. Those tools provide new ways to _create_ our code.

Consider Eclipse just a foundation for better things to come. Having Equinox OSGI container underneath it is fully modular ecosystem, that allows multiple bundles (in which we pack the plug-ins) coexist, and benefit from each others functionalities. Not dwelling on details of OSGI, it gives us a simple extensible platform to play with.

That in fact is great, because out of piles of Eclipse components you can build your own component base, and thus create a basis for your own solution. Since Eclipse is extensible you can extend the IDE’s workbench, by implementing plug-ins, or you can choose to implement a standalone application, that is based on RCP (Rich Client Platform) concept. And there are really big apps written with this in mind, like IBM’s Lotus Suite, totally based on Eclipse – and pretty neat also.

Well, that looks nice, but who writes so much code these days, who wants to create all the domain classes and GUI stuff by hand crafted api interfaces? Nope, one no longer have to go this path, just try Eclipse EMF sub-project, which offers model driven development practices, and whole bunch of code generation plug-ins will come to aid you. Using EMF you can create your domain model in just a few clicks, or import it from your existing java interfaces – actually you can use a couple more ways to do this. Having an EMF model you are just a few clicks from generating a working, domain editor, that would serve as a sandbox for your ideas about the domain you’re implementing, or it can be used right away in your new shiny web application.

Another few clicks and you get free model persistence with Hibernate, or other ORM framework. And this really works.

Since it would be nice to present things to end users you could generate some basic graphic editor, of course Eclipse supports that. But who uses thick clients today? Be serious, right? If you want something web-enabled, you don’t have to move your skills from the Eclipse ecosystem, just try out Eclipse RAP and have your Eclipse application in your browser via some serious Javascript voodoo magic – like on-the-fly converters. Of course other popular frameworks are allowed :)

What is most important here, is the constant use of the same tools, developing subsequent stages of the app don’t require you to switch skills. It’s Java all way up to this place.

And it gets more interesting when you dive deeper and deeper into this rich and flourishing community. Some examples of the vastness of the platform may be:

  • Swordfish – SOA solution, with BAM (Business Activity Monitoring) implemented
  • XText – enables you to write a simple (or not) DSLs for your apps
  • E4 – next gen Eclipse IDE, with many great ideas in it

Of course, the whole picture gets a bit blurry if you consider more technical details, there is not so much ease of use or scalability, etc, as you might expected. The whole Eclipse ecosystem may not be suitable for all your applications, but it may be for some. Or perhaps it is suitable for only a couple stages in your current project?

Let this be just a simple introduction to the rich Eclipse Community projects. With next iterations of this cycle I’d like to describe more in-depth details of the Eclipse framework, and various usage scenarios for Eclipse projects. Stay tuned!

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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.