The Four Types of Aspect-Oriented Programming (AOP) Weavers

At the Institute for Cyber Security, we use many different technologies to help accomplish our goals. One such technology is Aspect-Oriented Programming (AOP)., where one can "weave" cross-cutting concerns into source code, separating them from core concerns.

While compile-time weaving is common, the weaving process itself can take place at one of four different times: compile-time, post-compile time, load-time, and run-time. The run-time behavior of an application are the same regardless of the approach chosen.

• Compile-time weaving: this is the simplest approach. A compile-time weaver will compile from source and produce woven class files as output. The aspects themselves may be in source or binary form.
• Binary-weaving (also called post-compile-time weaving): this is used to weave existing class files and JAR files. As with compile-time weaving, the aspects used for weaving may be in source or binary form, and may themselves be woven by aspects.
• Load-time weaving: here, binary weaving is defered until the point that a class loader loads a class file and defines the class to the system. To support this, one or more "weaving class loaders", either provided explicitly by the run-time environment or enabled through a "weaving agent" are required. 
• Run-time weaving: this is the weaving of classes that have already been defined to the system without reloading those classes, making it a more dynamic load-time weaver.

Erhan J. Kartaltepe,
erhan.kartaltepe-at-utsa.edu

Implementing the Decorator Pattern in Java

At the Institute for Cyber Security, our software architects help fulfill the role of CTOs for new security startups, and will work with development teams to come up with technical solutions to existing development problems. In one recent example, one developer had to modify the behavior of an existing code base but could not modify the code due to licensing.

Normally, the solution is to subclass the original class, then add your behavior as necessary. However, in this case, the class was finalized, meaning the class could not be inherited. This stumped our intrepid developer--surely someone must have solved this problem before!

In software engineering, a design pattern is a general reusable solution to a commonly occurring software design problem. As you may have surmised from the title of this post, our architect recognized the issue and recommended the decorator pattern. This allows new behavior to be added to an existing class dynamically (assuming some design work had been done in advance) as an alternative to subclassing.

The decorator pattern is achieved by designing a new decorator class that wraps the original class. This wrapping could be achieved by the following sequence of steps:

1. Create an interface and the base "component" class that implement it.
2. Implement the interface into a "decorator" class.
3. In the Decorator class, add a Component "pointer" as a field;
4. Pass a Component to the Decorator constructor to initialize the Decorator's Component;
5. In the Decorator class, redirect all "Component" methods to the internal Component pointer and override any Component method(s) whose behavior needs to be modified.

This pattern is designed so that multiple decorators can be "stacked" on top of each other, each time adding a new functionality to the overridden method(s).

The above listing is best demonstrated by example.Consider the following: we have a Car class which has some functionality we'd like to modify, say by adding a top to the car or an engine. Listing 1 shows a Car interface and SimpleCar class.

Listing 1: Car Interface and SimpleCar Class

To add a top or an engine, we'd need separate classes for each functionality, and an abstract class that they extend (see Listing 2):

Listing 2: CarDecorator, TopDecorator, and EngineDecorator Classes

Using Listing 3, we can view the results of the Decorator pattern by calling the GetInfo method, which should return "car, with top, with revved engine".

Listing 3: DecoratedTest Class

In some dynamic languages, this can be more easily achieved, but in Java, this seals the deal and our developer was able to walk away, not only with a solution to his specific problem, but with a broader understanding of design patterns in general.

Erhan J. Kartaltepe,
erhan.kartaltepe-at-utsa.edu

Free Online JavaFX Class

Sun released JavaFX last month, to overall positive reviews. JavaFX differs slightly from applets in that they aim to allow rapid application development of slick RIA apps like those produced by Flash or Silverlight, but also allow developers to program apps that will run on meager devices such as cell phones and other handheld devices.

If you're interested in JavaFX, and JavaFX tutorials aren't enough for you, there is a free fifteen week JavaFX class being offered by Jim Weaver and Sang Shin. It's an online course that starts next Friday (January 30) and "meets" weekly. Enjoy!

Erhan J. Kartaltepe,
erhan.kartaltepe-at-utsa.edu

Mobile Development, Part Three: RIM BlackBerry

This is part three in a five part series. Click here for part one. Click here for part two.

Microsoft was a heavyweight in the computing and browsing markets when it entered the handheld world. Like its desktop operating system, Microsoft has multiple versions of its embedded OS, under such monikers as Windows CE, PocketPC, Portable Media Center, Windows Mobile Classic, Windows Mobile Professional, and Windows Mobile Standard. In this manner, Microsoft had an OS for every taste. Compared to this, Research In Motion (RIM) positing the BlackBerry hardware and with its one operating system seems to be contrary, yet RIM maintains the enterprise market share for handheld devices.

Part III: RIM BlackBerry

Where Microsoft attempted to take its desktop knowledge to the handheld world, RIM started in the handheld world and "worked its way up". While originally focused on embedded systems, RIM hit the jackpot with the BlackBerry and Good devices.

Like Windows Mobile and unlike Palm OS, the BlackBerry OS is multithreaded, allowing for multiple applications to run at the same time. Most applications written for the BlackBerry are in C++ and Java, though for some underlying capability applications must be digitally signed with a trusted certificate authority, which can put a barrier to more sophisticated applications for hobbyists.

C++ and Java are very open, and with Eclipse or NetBeans, tools and addons exist that support rapid application development. Java's Mobile Edition in particular has a rich subset of the common Java libraries, similar to how the .NET compact framework assists in producing sophisticated applications for Windows Mobile, including its cryptographic and socket libraries. Additionally, all BlackBerry models utilize Trible DES or (more recently) AES for wireless communication a priori, saving the developer the trouble of encrypting and decrypting data sent over the wire(less).

For a while, RIM and Microsoft split the smartphone/enterprise handheld market, but tomorrow we will visit the system that was predicted years before it came out, and still exceeded expectations, taking not only a large share of the enterprise market, but the consumer share as well.

Erhan J. Kartaltepe,
erhan.kartaltepe-at-utsa.edu

What the Future Holds for Java 7

JavaWorld just published an interesting article on what users can expect from Java 7. Topics such as dependency management, more NIO (new I/O) enhancements, parallelism, language changes (though, sadly, perhaps not closures), and dynamic language support are discussed. If you're a fan of Java like the developers at ICS, this article should whet your appetite for Sun's latest Java release.

(Image is completely apropos--it's a Java sparrow, a songbird native to Indonesia)

Erhan J. Kartaltepe,
erhan.kartaltepe-at-utsa.edu

Python 3.0 and JavaFx 1.0 Released Today

This morning, Python announced the much anticipated release of Python 3.0. While I'm not a huge Python guru, I have been looking forward to its official release, since it cleans up some archaic remnants of older iterations and standardized its syntax. A great set of documentation is available, including beginner's tutorials and language reference. Scripting languages like Python and PHP are in heavy use at the Institute for Cyber Security, and bold releases like this bolster mainstream support for them.

Hot on its heels, Sun announced the release of JavaFx. Some JavaFx tutorials are available. Much of the work at the ICS includes client-side software meant to run within a browser, and uses technologies such as JavaScript, Flash/Flex, and Silverlight daily. Sun's Java applets are perhaps an unfair callback, but the idea of a Java program, complete with Swing and other GUI components, running in the user's browser is very much alive in JavaFx. Hopefully Sun has better luck this go around, while simultaneously providing Adobe and Microsoft with some competition.

Erhan J. Kartaltepe,
erhan.kartaltepe-at-utsa.edu