Sunday, April 27, 2008

To Spring or not to Spring

Just got back from a few days in the Netherlands and Belgium, where I gave technical sessions at a few knowledge events organized by our partners in the region.
One of the events was held by our Dutch affiliate, Tricode, which did a great job in setting it up and attracting quite a few developers and architects to it. We even have a GigaSpaces Dutch web site now which Tricode guys have set up for us - so thanks guys.

One of the questions I got after the session was something in the following spirit:
"Sure, Spring is great and OpenSpaces integrates very nicely with it which is great. But what if I don't like all this XML in my project, or just (imagine that) don't use Spring but still want to use OpenSpaces APIs which are clean and nice"?

Of course, you can always "imitate" Spring and call the OpenSpaces Spring factory beans from your own code, but that's not very clean and will require you to dig through the OpenSpaces code to understand how things work.
Thankfully, you have another option - OpenSpaces configuration API, aka OpenSpaces configurers. It's fairly new (6.0.2 onwards) and therefore is still relatively unknown to many of our users.

Some (pretty recent) History

Up until version 6.0, the preferred API to use GigaSpaces was JavaSpaces with proprietary extensions. In 6.0 we introduced OpenSpaces, which greatly simplified things and made the user experience much more positive by abstracting away lot of the API problems and inconsistencies.
From day 1, OpenSpaces has been all about Spring: It uses Spring for configuration and utilizes a lot of goodies that Spring provides such as transaction management framework, namespace based configuration, etc.
But since OpenSpaces' goal is become the preferred Java API for the product, the fact that you can only use it through Spring was a bit limiting to some of our customers and prospects.
In addition, the trend towards code based configuration (first with Guice and now also with Spring Java Config) also made us realize that we need a way to use OpenSpaces interfaces without wiring them through XML.

Configurers Demystified
So here are a number of snippets to show you how this is done. Let's first show the Spring equivalent creating a space instance and then wiring your listener on top of it using a polling container:
<os-core:space id="space" url="/./space" />

os-core:giga-space id="gigaSpace" space="space"/>

bean id="simpleListener" class="SimpleListener" />

os-events:polling-container id="eventContainer" giga-space="gigaSpace">

<bean class="">
<property name="processed" value="false"/>

<os-events:delegate ref="simpleListener"/>

The above XML snippet creates a space and registers to get notified on all objects of type Data whose processed field equals false. Here's how this is done in java code, via configurers:
//creating a space
IJSpace space = new UrlSpaceConfigurer("/./space").space();
//wrapping it with a GigaSpace
GigaSpace gigaSpace = new GigaSpaceConfigurer(space).gigaSpace();
//creating polling container
Data template = new Data();
SimplePollingEventListenerContainer pollingEventListenerContainer =
new SimplePollingContainerConfigurer(gigaSpace)
new SimpleListener())

That's it. as you can see, it's even simpler than the XML equivalent.
A few interesting things about this:
  • All our configurers use method chaining, which makes them very intuitive to use. It's about as close as you can get to domain specific languages in pure Java :)
  • There are configurers for all of the OpenSpaces constructs, specifically: Space, GigaSpace, Event containers, Remoting Proxies and Scripting Proxies.
Where is this documented?
Every OpenSpaces docs page includes XML snippets that show the configuration.
Every such XML snippet is displayed in a tabbed pane, which typically has 3 tabs:
  • Namespace - which stands for the default configuration using Spring's namespaces support.
  • Plain XML - which shows how to configure the component via pure spring, without GigaSpaces specific namespaces
  • Code - which shows how to configure the component using configurers
Here's a screen shot to illustrate this:

No comments: