Dynamic DataSource Routing

Engineering | Mark Fisher | January 23, 2007 | ...

Spring 2.0.1 introduced an AbstractRoutingDataSource. I believe that it deserves attention, since (based on frequent questions from clients) I have a hunch that there are quite a few 'home-grown' solutions to this problem floating around. That combined with the fact that it is trivial to implement yet easy to overlook, and now I have several reasons to dust off my corner of the team blog.

The general idea is that a routing DataSource acts as an intermediary - while the 'real' DataSource can be determined dynamically at runtime based upon a lookup key. One potential use-case is for ensuring transaction-specific isolation levels which are not supported by standard JTA. For that, Spring provides an implementation: IsolationLevelDataSourceRouter

Java to JavaScript Compilation with AJAX and Spring Integration

Engineering | Ben Alex | January 22, 2007 | ...

For some time I have been interested in client-centric, web-based user interfaces. These Generation IV frameworks are characterised by their component-based, event-driven programming model, and focus on the presentation logic residing entirely on the client. Targeting a web browser in this manner typically necessitates the use of JavaScript or Flash, which in itself imposes a number of unique challenges.

It is possible to address many of these challenges if we can program in Java and automatically produce a JavaScript or Flash runtime module. Two well-known products for achieving this today are Google Web Toolkit (GWT) and Open Laszlo respectively. Both are available under OSI-approved licenses and have active communities, together with their own unique complexity. One consideration is to what extent they fulfil an objective of providing a transparent Java-based development environment that targets web browser deployment. This consideration has several facets, including IDE support, debugging integration, reflective capabilities, runtime widget binding and alike. All of…

Spring IDE powering ahead

Engineering | Rod Johnson | January 21, 2007 | ...

I had a great time at the Spring Experience conference last month. One pleasant surprise I had was the extent of the recent work the Spring IDE team have been doing. I ran into Spring IDE developer Christian Dupuis several times at the conference, and it seems that each time he'd implemented a new feature...

The forthcoming 2.0 release of Spring IDE is a comprehensive update to match the new features in Spring 2.0. And the Spring IDE team is making great progress with two of the big ticket items: XML extension namespaces and the AOP enhancements. (Btw, in case you're wondering why I haven't posted for a while, I spent a lot of time writing a Spring 2.0 update article over at InfoQ

Installing WebSphere Application Server 6.1 on Ubuntu

Engineering | Rob Harrop | January 19, 2007 | ...

Recently I've been doing some work with a client on WAS 6.1. Since we have a number of Spring users on WAS and I need to test the application, I decided it was time to get a copy of WAS running on one of my work laptops. I say 'one of' because I'm currently working on both my Mac (with OSX) and my ThinkPad (with Ubuntu) - more recently I've just been using the ThinkPad because I can have Oracle XE and WAS running without the need for a VM tool like Parallels. I still prefer the Mac, but to be honest there isn't much difference day-to-day - I just miss some of the more useful Mac tools like Spotlight, Quicksilver, TextMate and NewsFire.

Anyway, back to the main topic - installing WAS 6.1 on Ubuntu. I'm using Ubuntu Edgy and my first attempts at an install failed completely and I just couldn't figure out why. Thankfully a quick Google turned up this article. I was completely unaware that /bin/sh was linked to dash instead of bash - what on earth possessed them. I didn't really like the suggested solution of running the installer, letting it fail and then changing all the scripts in the installed directory. Instead, I just relinked /bin/sh with a quick sudo unlink /bin/sh followed by sudo ln -s /bin/bash /bin/sh. After that, the installer ran like a dream and I was up and running with a WAS install in about 15 minutes.

Even on my ThinkPad with Oracle XE running at the same time, WAS runs pretty quickly. One of the nicest things about WAS is that the tools provided (admin console, command-line tools) are really robust. The Admin Console is noticeable for its performance - many other servers have consoles that are painfully slow.

A Bridge Too Far

Engineering | Rob Harrop | January 16, 2007 | ...

In my last entry I presented a technique for creating strategy classes that take full advantage of any generic metadata that is present in your application. At the end of that entry I showed this code snippet:

EntitlementCalculator calculator = new DividendEntitlementCalculator();
calculator.calculateEntitlement(new MergerCorporateActionEvent());

You'll remember that DividendEntitlementCalculator was defined as:

public class DividendEntitlementCalculator implements EntitlementCalculator<DividendCorporateActionEvent> {

    public void calculateEntitlement(DividendCorporateActionEvent event) {

    }
}

As such it is not correct to pass an instance of MergerCorporateActionEvent into the calculateEntitlement method of the DividendEntitlementCalculator class. However, as I mentioned in my last entry that code will compile. Why? Well, EntitlementCalculator.calculateEntitlement() is defined to accept any type that extends CorporateActionEvent so it should compile. So in this scenario what happens at runtime and how does Java enforce type safety? Well, as you might imagine running this code gives you a ClassCastException saying that you cannot cast a MergerCorporateActionEvent to DividendCoporateActionEvent. In this way, Java can enforce type safety for you application - there is no way that the MergerCorporateActionEvent can creep into a method where DividendCorporateActionEvent is expected.

The real question here is: 'Where does that ClassCastException come from?' The answer is pretty simple - the Java compiler adds the code to create and throw it as appropriate by introducing a bridge method. Bridge methods are synthetic methods that the compiler will generate and add to your classes to ensure type safety in the face of generic types.

In the case shown above EntitlementCalculator.calculateEntitlement can be called with any object that is type compatible with CorporateActionEvent. However, DividendEntitlementCalculator accepts only objects that are type compatible with DividendCorporateActionEvent, but, since you can call the DividendEntitlementCalculator via the EntitlementCalculator interface it too must accept CorporateActionEvent. So what does this translate to in the compiled class file? We have the user supplied method:

public void calculateEntitlement(DividendCorporateActionEvent event) {
    System.out.println(event);
}

Which translates to this bytecode:

public void calculateEntitlement(bigbank.DividendCorporateActionEvent);
  Code:
   Stack=2, Locals=2, Args_size=2
   0:   getstatic       #2; //Field java…

Unit Testing with Stubs and Mocks

Engineering | Dave Syer | January 15, 2007 | ...

I was on site with some clients the other day, and they asked me about unit testing and mock objects. I decided to write up some of the discussion we had as a tutorial on creating dependencies (collaborators) for unit testing. We discuss two options, stubbing and mock objects and give some simple examples that illustrate the usage, and the advantages and disadvantages of both approaches.

It is common in unit tests to mock or stub collaborators of the class under test so that the test is independent of the implementation of the collaborators. It is also a useful thing to be able to do to…

What's New and Cool in Spring 2.0?

Engineering | Ben Alex | December 16, 2006 | ...

Last month Rod Johnson presented at three Australian Spring User Group meetings a session entitled, "What's New and Cool in Spring 2.0". Rod mentioned during those meetings that I'd make his presentation available, so here it is.

There are some other recent presentations that people have also been emailing me about. In no particular order, here is the latest:

For those of you who attended the presentations, I hope you enjoyed them.

Why the name Interface21?

Engineering | Rod Johnson | December 16, 2006 | ...

A few weeks ago I blogged about the origins of the name Spring. We also get many questions about the origins of the name Interface21.

For anyone who's read my books or considered the design of Spring, the interface part is hardly a surprise. It plays on both the OO concept of an interface (for which I've always had a deep love) and the notion of the interface to a system. For example, putting a web interface onto an existing green screen system--something I was actually doing when I first thought of the company name.

So far, so good. The real problem is with the numbers.

As with the name Spring, some of the theories are more interesting than the real explanation. So let's start with the theories I've heard regarding the 21

What happened to getConfigLocations()?

Engineering | Ben Hale | December 08, 2006 | ...

I was on site at a customer last week and a question came from the crowd, "Why isn't getConfigLocations() abstract anymore?" After working in front of customers for a while, it becomes rare that you're speechless, and yet I was. To be honest, my first thought was that there was no way the customer could be right. But lo and behold, in revision 1.3 of AbstractSingleSpringContextTests it clearly states that getConfigLocations() is no longer abstract. I hadn't created any new integration tests against 2.0.1, so I hadn't even seen the change.

Surprised by this, I put in an email to Juergen to…

What you have to look forward to at The Spring Experience 2006...

Engineering | Keith Donald | November 30, 2006 | ...

These shots of our venue were taken yesterday (proximity to places like this is one of the perks of Interface21 having an office in Florida).

 
The Majestic Westin Diplomat
Complete with an infinity pool
A lazy river underneath
On beautiful beach-front property

We are incorporating several of these shots into the main conference banners to be draped from the towering ceilings of the Diplomat. Everything is set for a great show. See you at The Spring Experience next week!

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