Develop Aspect-Oriented Java Applications with Eclipse and AJDT
By Matt Chapman, Dr. Helen Hawkins2005-05-16
Aspect Visualization perspective
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If you're going to write aspect-oriented applications, you'll benefit from new ways of visualizing those applications. You need to be able to understand the relationships between your aspects and classes, and get an overall feeling for how your application behaves. For instance, how many classes do your aspects affect? As already described, AJDT provides advanced capabilities for navigating around your code, showing what is being advised, and so on. Building on this foundation, AJDT also provides its own Aspect Visualization perspective. This feature is specifically designed to help you view the crosscutting concerns in your application. To activate this perspective, go to Window>Open Perspective... and select Aspect Visualization. You should get a display that looks like Figure 10.
Figure 10. Visualization perspective
After you've opened this perspective, you'll notice that the focus is on visualization rather than coding. The main visualization tool integrated into the Aspect Visualization perspective is the Visualiser, located in the center of the perspective. If you've used earlier versions of AJDT, then the Visualiser is nothing new to you; however, in previous releases it used to be part of AJDT, whereas now it's a standalone plug-in. This means that it's possible to write your own provider to use the Visualiser to view your own data (for more information about the Visualiser select Help>Help Contents>Visualiser). In the Aspect Visualization perspective, though, we're using the AspectJ provider, as you can see in Figure 10. This represents the classes and aspects within a project as bars and the places where aspects affect your code as stripes on those bars. The lengths of the bars are relative to file size -- the longer the bar, the more lines of code there are in the file that bar represents!
To populate the Visualiser, just select an AspectJ project in the Projects view on the far left, or a package in the Package view to the right of that. Look at the Spacewar example, and you 'll see that there are some bars that are greyed out, some bars with only one colored stripe, and some bars with more than one colored stripe. (Sometimes there's even more than one stripe on a single line!) The greyed-out bars represent classes or aspects that are not affected by any advice. By pressing the button shown in Figure 11, you can choose to filter out these unaffected bars.
Figure 11. The Visualiser controls
Look at the remaining affected bars and their stripes, and you'll see that the colors match those on the buttons in the Visualiser menu (located to the right of the Visualiser). Next to each of the colored buttons is a checkbox and a label. The label gives the name of the aspect (or class that contains the aspect, in the case of inner aspects) that the color represents, and the checkbox indicates whether or not this aspect has been included in the current visualization. Thus, if you have several aspects, you can filter out any aspects you're not interested in. For example, if you build the Spacewar example with the debug.ajproperties build configuration and then return to the Visualiser, you may decide that you just want to see what your Debug aspect is affecting. Deselecting all but the Debug aspect in the Visualiser menu shows you precisely this, as you can see in Figure 12. Another way to tell which color represents a particular aspect is by mousing over the stripe you're interested in. This gives the name of the aspect that stripe represents. If there's more than one color to a stripe, then there's more than one aspect affecting that line of code!
Figure 12. Visualizing the effects of the debug aspect
Another very important feature of the Visualiser is that it too provides a way of navigating around your code. Having looked at the visualization of the Spacewar example, we can see that there is a Display aspect. We haven't looked into the code yet, so you're probably curious as to what this aspect does. We can see that it affects four classes, but what are they? Mousing over the dark grey stripe at the top of the bars for each of these affected classes, we find out that they are spacewar.Display, spacewar.Game, spacewar.SWFrame, and spacewar.Timer. But what exactly is the aspect advising? Double-click on the stripe on the spacewar.Game bar and you'll see: You go straight to the point in Game.java that is affected by the Display aspect, and it appears in the Editor view at the bottom of the Aspect Visualization perspective.
Tutorial Pages:
» Updated tools make AOP easier for beginners and veterans alike
» Installing AJDT
» First steps
» The Outline view and editor markers
» The Spacewar example
» Build configurations
» Aspect Visualization perspective
» Debugging
» Generating documentation
» Further options
» Conclusion
» Resources
First published by IBM DeveloperWorks
