Aspect Oriented Programming – Part 1
Today, I’m going to start new series of tutorials on a new topic. i.e. Aspect-Oriented Programming, in which you will learn about the new programming paradigm (though it’s too old), its basics, the core concept, comparison with current programming paradigms like Object Oriented Programming (OOA) and finally implementation for any real-world problem or scenario.
I will post 3, 4 articles for this topic, dividing this into the following possible sections
- Object-oriented programming approach and some flaws
- The core theme of Aspect-Oriented Programming
- Solutions provided by AOP against OOP flaws
- Important terms used in AOP talk
- A programming example with OOP and AOP
- Introduction of AspectJ, a java implementation of the aspect-oriented approach.
Object-Oriented Programming Approach
Computer software or programs are automation of real-world scenarios, a transformation of manual work into computer-operated systems. Many approaches are in practice to design and develop more usable, user-friendly, easily evolvable and maintainable computer systems. Different approaches handle the under-considerate domain with their own style. The object-oriented approach focuses on data, takes anything in the real world as data having some attributes (data fields) and some operations (methods). This approach evolves in the sixth decade of the last century when the computer system becomes much more complex and the current programming paradigms were not much capable to cope with required features to facilitate both developers and end-users. At that moment researchers made on some new style of programming and then introduced a “data-focused” approach. i.e. object-oriented programming where everything in real life was considered an object, in other words, every noun is an object. We design systems based on these nouns in real-world like Pay, Account, Employee, Product, PurchaseOrder, Invoice etc
The object-oriented approach was at its peak in the mid-’80s and late ’90s, even still a great number of computer systems are being developed using the object-oriented approach, but from its birth, it is faced many critics. Though the implementer of this approach is introducing many new features day by day in their respective languages compilers but only adding feature after feature into something don’t make it better. Polymorphism, encapsulation, abstraction no doubt are building blocks of any mature programming language and should be available implicitly, yet still, there are few areas where developers need more ease and re-usability of their efforts and code. Those areas were perceived and made research and then a new approach was presented to design and develop software modules with more ease in re-usability of existing code, more ease in extendability and maintainability. This approach was AOP.
Did you ever feel that while developing in an object-oriented world, you have you rewrite the same chunk of code in different classes/methods to achieve the same goal? like (as a very simple example) in the data access layer, you have to open a database connection, maintain its session, write a query, call to the database to fetch data and at the end, close the database connections and sessions. Like following
method Fetch_Employee_DATA{
open database session;
create a query to fetch data;
call to the database to fetch data;
close database session;
return results;
}
here the bold text is those lines of code you have to write in each method you call to fetch data from the database, other lines are method-specific and depends upon the business logic.
Like the other example, if you have to log each and every database call. i.e. the query to the database, its parameter, the returned results etc, then you have to write the same line of codes every time in each method that is going to interact with the database. The above method will look like
method Fetch_Employee_DATA{
log the start of method;
open database session;
create a query to fetch data;
log query and its parameters;
call to the database to fetch data;
close database session;
log returned data from the database;
log end of method;
return results;
}
Again the bold lines are those lines of code you are replicating in each method to achieve the same goal. Don’t you think you’re spending a lot of time writing the same bits of code when it comes to implementing the individual methods? These things like logging, security checking, transaction management are such aspects of the systems that are orthogonal to the specific application. Every organization need them and every developer has to implement them in their respected module, classes and methods. In short, the method hasn’t concern with these replicated lines, or the core concern of the method is to fetch employees, not to log database transactions, session maintenance etc. Every class or method is doing something extra time and again that doesn’t concern their core requirement.
For small projects for small level organizations, it may work. But what if you are going to design and develop a banking system, an ERP for a large scale company, or a payroll system for a big industry … where the modules are interlinked cohesively, the domain is very large, covering all business scenarios of under-considerate organization. In such a system, you can’t afford such a framework and design that is difficult to extend, maintain and reuse. You can’t let your developers spend time and resources over rewriting the same bit of code in every class and method, instead of focusing core business logic of that class. In other words, you can’t let everyone focus on those things that are not concerned with their core task.
Consider the above example again. You are working on a project (let’s suppose inventory management). While developing different features or modules, you have to call the database to fetch and insert data as per business logic and domain requirement. We have seen that in every method you write, you are writing the code of opening the database session and closing it properly. In a medium and large scale project, the number of methods doing the same things could be hundreds. Anyhow, you complete your task and deploy the application at the client site. Next time you are asked to maintain logs for each database interaction (as we discussed above) you instantly recall the number of classes and methods where you have to write code related to logging …. you have more than 40, 50 classes (let’s suppose) and there are hundreds of methods interacting with database. You have to open each method’s body and has to write logging code there
“Sir it will take atleast 4,5 days to complete this task”
“4, 5 days, but way, its really a simple task”
“indeed its simple but i have review each and every package, class and method to embed logging code there. To make sure the sustainability of application, i have to test it thoroughly to check that our existing application are new changes are running fine”
“hmmm ok, add someone else with you and try to complete it within 2,3 day, there are lot of other things too to do”
“sure i will”
This is the expected dialog between a developer and his manager/team lead while incorporation a simple change in running application. See, the actual lines that has to write in every method are very simple, just 2, 3 lines. But when it span over entire application with hundreds of packages/classes/methods then it becomes worst, consuming your more resources in term of human effort, time and budge.
Think again … is the logging concerned to method which was written to fetch data from database? Should a developer concern with database issues like opening a session and closing it properly who want to focus his attention to design an optimal query to fetch data from database?
In next post i will introduce Aspect Oriented Programming (AOP) and will discuss how AOP provides solutions for problems we discussed earlier.
Ans, its really a good post. you keep your style simple and understandable. I’m waiting for next post … plz be quick
Its quite helpful and great work.
Thanks athar for reading the post and for your comments. i will try my best to make it more simple in understanding.
kindly find 2nd part of this series at
http://aasims.wordpress.com/2009/11/04/aspect-oriented-programming-part-2/
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