If not, this is for you! Nowadays, I see a lot of projects using all the latest technologies made in Spring Boot and other cutting-edge frameworks. On one hand, it sounds promising, but on the other hand, I often see that developers are not taking full advantage of the technologies in front of them.
I think it is primarily because a majority of books and documentation are too academic and difficult to understand. That is why I decided to talk a bit about aspect-oriented programming. Aspect-oriented programming is a programming paradigm that tries to solve problems with cross-cutting concerns.
Aspect-oriented programming AOP complements object-oriented programming OOP by providing a different way to think about program structure. In a more simpler word, it helps us to refactor the different necessary repeating codes into different modules. This gives us the benefit that we can maintain these functionalities in one single place, instead of it writing down every time.
This approach will result in a much more maintainable code, which clears the business logic from the most confusion factor.
We separate these functionalities along different aspects. An aspect is a modularization of a concern that cuts across multiple classes. Unified logging or transaction management can be a good example of it.
Here, you can recognize a couple of different concerns, which are not related to the business logic itself. We should separate these into another place. Henceforward, only the business logic has left. If you have a system that contains several packages and classes that you do not use with AOP, such as tracing, transactions, and exception handling, we have to implement them in every class and every method.
Using AOP allows you to solve these problems. So, what AOP does is it takes all the transaction code and puts it into a transaction aspect. Then, it takes all the tracing code and puts that into an aspect.
Finally, exception handling is put into an aspect. Understanding Scenario I have to maintain log and send notification after calling methods that starts from m. Problem without AOP We can call methods that maintains log and sends notification from the methods starting with m. In such scenario, we need to write the code in all the 5 methods.
But, if client says in future, I don't have to send notification, you need to change all the methods. It leads to the maintenance problem. Solution with AOP We don't have to call methods from the method. Now we can define the additional concern like maintaining log, sending notification etc.
Its entry is given in the xml file. In future, if client says to remove the notifier functionality, we need to change only in the xml file. So, maintenance is easy in AOP. Join point is any point in your program such as method execution, exception handling, field access etc.
Spring supports only method execution join point. Advice represents an action taken by an aspect at a particular join point. There are different types of advices:. It means introduction of additional method and fields for a type. It allows you to introduce new interface to any advised object. It is the object i. It is also known as proxied object in spring because Spring AOP is implemented using runtime proxies.
It is used to implement aspect contracts, created by AOP framework. It is the process of linking aspect with other application types or objects to create an advised object. Weaving can be done at compile time, load time or runtime. Spring AOP performs weaving at runtime. Spring AOP can be used by 3 ways given below. The 3 ways to use spring AOP are given below:.
JavaTpoint offers too many high quality services. Mail us on [email protected] , to get more information about given services. Please mail your requirement at [email protected] Duration: 1 week to 2 week. Spring Tutorial. A more general way to specify pointcuts is to directly tag the joinpoints in the application code using annotations. Then, in the jboss-aop. In the following jboss-aop. Notice that you do not need to annotate the aspect class anymore in this setup.
The ability to specify pointcuts via annotations in the application code allows us to develop pre-packaged aspects and then publish the annotation API for all to use. The aspects you have seen so far are "interceptor" type aspects. Another key AOP feature is "introduction" or "mixin" of classes from independent inheritance trees. An introduction modifies the type and structure of a Java class. It can be used to force an existing class to implement an interface using methods from another class.
The following example shows that the methods in FooMixin class is used to make Foo class to implement the FooMixinInt interface at runtime. Here is the FooMixinInt interface. However, the Foo class does not implement the FooMixinInt interface. The following jboss-aop. Then, in the application code, you can cast a Foo instance to the FooMixinInt type at runtime. Building JBoss AOP applications is slightly different from building plain Java applications since the aspects and advices need to be instrumented into the compiled Java bytecode.
For example, if an advice is bound to a method invocation joinpoint, the AOP instrumentation process would modify the joinpoint bytecode to call out to the advice method with the properly composed invocation object as an argument. The first step is to compile the all classes, including the aspect classes, to bytecode using the regular javac utility.
If you use JDK 5. You can skip this step if you use Java annotations with the JDK 5. They are not processed by the javac compiler. The annotation compiler can directly add annotation to the bytecode class files or generate the annotation data in a separate XML file called metadata.
The following example compiles the annotation in Foo. The following example compiles the annotation into a metadata. The metadata. You can also run the annotation compiler within an ANT build script. The following example modifies the Java bytecode class files directly to add annotations. In this book, we build applications using ANT. So, the ANT version of the annotation compiler is used. The AOP instrumentation process modifies the Java bytecode to add runtime hooks around pointcuts.
Those hooks collect reflection information and invoke advices. It takes pointcuts definition from the jboss-aop. The following example shows how to invoke aopc from the command line with an associated jboss-aop. If both jboss-aop. The following example shows how to invoke aopc within an ANT build script. The aopc instrumented bytecode can run directly in any JVM.
Another option is to instrument the bytecode at the class load time. This way, you do not need to run the separate aopc program. In fact, if you use JDK 5. The jboss-aop. The structure of the jboss-aop. Please notice that the jboss-aop. It includes the following components:. A pre-packaged set of aspects, which are available in all applications deployed on the server.
Those pre-packaged aspects handle crosscutting concerns, such as security, transaction and spawning asynchronous threads, for applications. A default aspect binding configuration file base-aop. It binds pre-packaged aspects to certain annotations and method signature patterns. So, in your applications, you can just use those pre-defined annotations and method signatures to take advantage of the pre-packaged aspects.
Figure You can just copy those files to your JBoss server's deploy directory to replace the JBoss AOP service shipped with the application server. By default, the jboss-aop. You have to instrument your code offline with the aopc utility. You can just change the EnableTransformer attribute value to true as follows. The key value proposition of AOP is to promote code reuse. For example, we can reuse common aspects across different object trees in different applications.
You can inject the current transaction manager anywhere in the code via annotation and save the trouble to write lookup code. We cover an security aspect example later in this chapter. For example, the observer could log all the call invocations against methods in the object. The previously mentioned trace example shows the observer in action.
This aspect can be used outside of the JBoss AS in standalone applications.
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