What is the Difference between Spring IOC and Spring AOP and their Importance ?
Have you searched the web for IoC and AOP? There are a lot of references to both.
In a nutshell, IoC allows an external force to determine what implementation will be used by code rather than the code determining the implementation. The "external force" might be a configuration file, a unit test, other different code, etc.
AOP allows cross-cutting concerns to be implemented outside of the code affected by those concerns.
The "purpose" of Spring includes IoC and AOP, but goes quite a ways beyond that in its scope.
For more details please check.
Inversion of Control Containers and the Dependency Injection pattern and
Aspect-oriented programming
Also check this
What is AOP, Dependency Injection and Inversion Of Control in Simple English
IoC, AOP and more
Spring IOC: In simple answer normally you create object with new operator and set yourself for getter and setter. So, yes we use new operator in Java to create object. There is no any bad in doing this. But, when your project size grows and lots of developers are working, and you want to achieve POJO-based programming, you can use DI. So then maybe your question arises - why I can not code it myself? Of course you can use the power of reflection, annotation, and XML. But, some other had already coded this then why not reuse the third party one? There are lots of options for you to choose; Spring can be the best one. It manages your object life cycle from object creation to its destruction. You use the objects created and set by Spring DI container but you do not create them yourself.
Spring AOP: It is related to cross cutting concern. What it mean is in large system the common functionality is scattered throughout different modules. So AOP provides an easiest way to take out a common implementation in the form of 'aspect'. You can also in this case write own implementation using proxy concept but you can reuse the code of proxy based that is implementation of APO alliance using Spring.
Objective of Spring IOC is to reduce explicit dependencies between components, while purpose of Spring AOP is to wire components together possibly by enforcing certain common behavior (read: NOT Interface)
Since purpose of Spring AOP is to enforce certain behavior across components.So, Spring IOC comes in handy to achieve this purpose
Related
I am using Hexagonal Architecture, Hibernate Reactive with Panache and Quarkus in a Kotlin Project.
Transaction boundaries are set using #ReactiveTransactional annotation.
The problem is that I had to add the whole Hibernate Reactive with Panache dependency in the domain and application layers just to make this annotation available.
Is there a way to avoid this?
I was hoping it would be possible to create a domain annotation and then in the adapters layer replace it with the #ReactiveTransactional somehow.
You could remove the annotation from the class, and wrap it into a service, and implement this service in the adapter layer using the annotation.
Don't use database related dependencies inside the hexagon.
The idea is to decouple the business logic from the user interface and infrastructure. Database logic should be placed into an adapter.
It theory it sounds great, in practice that means tons of mappers i.e. boilerplate code. On the bright side you have a Kotlin, and not a Java project so this should be a bit less tedious than the alternative. Bear in mind that there are projects such as Dozer, MapStruct that can make the mapping process easier.
I am reading spring docs this site.
and I already have knowledge IoC(or DI) and AOP a little bit.
While reading docs, I read this phrase.
Foremost amongst these is the Spring Framework’s Inversion of Control (IoC) container. A thorough treatment of the Spring Framework’s IoC container is closely followed by comprehensive coverage of Spring’s Aspect-Oriented Programming (AOP) technologies.
As far as I know, IoC is how Container creates instances and injects them when needed, and AOP is perspective-oriented programming;How you can focus on what you want to do.
However, I understand the above phrase that AOP works well thanks to IoC.
I'm not sure what's the relationship between the two.
Wait for a good answer.
An IoC framework allows injection of an implementation through an external influence, typically configuration.
AOP's purpose is to enable loose weaving of other concerns into business logic code without direct modification of the code.
Spring is a framework that extensively uses AOP to enable implementation of IoC.
There is a whole lot of reading material on both patterns available on the web.
For IoC start here. For AOP, I found this helpful.
AOP concerned mainly with abstracting functionality that applies across the board to many components of your application. for example logging and security. These have little or nothing to do with actual business functionality but are essential system-wide functions
IOC or Di is mainly loose coupling and managing the dependencies between the component of an application.
Both IOC and AOP are made possible through having your code managed by some sort of run-time container.
The container injects dependencies into your constructors and property setters, instead of you doing it manually. The motto for Spring is/was: "Creating objects so you don't have to."
Once your code is running in a container, it's a simple enough matter to introduce AOP concepts which boil down to executing code before or after what's being managed by the container.
IOC and AOP are sibling practices made possible by a run-time container. Start with a IOC container and it's easy to introduce AOP features. Start with an AOP container and IOC features easily follow.
I have read that dependency injection is good for testing, in that a class can be tested without its dependencies, but the question comes to my mind if Class A depends on Class B or C or any class, testing Class A independent of some class is yielding a test result of zero, not a failed or past test.
Class A was created to do something and if it is not fed anything whether using new key word or setting up the extra files in Spring, Class A won't do any work.
About the idea of making code modular, readable and maintainable: so business classes became cleaner, but all we did was shift confusion from dirty Java business classes to convoluted XML files and having to delete interfaces used to inject to our loosened objects.
In short, it seems we have to make edits and changes to a file somewhere,right?
Please feel free to put me in my place if my understanding is lacking, just a little irritated with learning Spring because I see the same amount of work just rearranged.
Dependency injection is good for unit testing because you can individually test each method without that method depending on anything else. That way each unit test can test exactly one method.
I would say that if the xml is what’s annoying you check out Spring boot. It’s based on a java configuration so no xml and it simplifies a lot of configuration for you based on your class path. When I first started spring I found the xml very daunting coming from a java background but the annotation based configuration and the auto configuring done by spring boot is extremely helpful for quickly getting applications working.
IMO biggest advantage of using the spring is dependency injection which makes your life easy. For example if you would like to create a new service with three dependencies, then you can create a class very easily using Spring. But without spring, you will end up writing different factory methods which will return you the instances you are looking for. This makes your code very verbose with static method calls. You may want to take a look at the code repositories before spring era.
Again if you would like to use Spring or not is your personal call based on project complexity. But it's other features/advantages cant be overlooked.
And XML files or Java configs are the ways of achieving spring configuration - where you would like to add your business logic is personal flavour. Only thing is you should be consistent all across your project.
I would suggest that you read Martin Fowler's great article on Inversion of Control and Dependency Injection to gain a better understanding of why frameworks like Spring can be really useful to solve a well known set of common dependency injection problems when writing software.
As others have mentioned, there is no obligation to use Spring; and whatever you can do with Spring, you can probably do it by other means like abstract factories, factory methods, or service locators.
If your project is small enough, then you probably wouldn't mind solving the dependency injection issues on your own using some design patterns like those mentioned above. However, depending on the size of your project, many would prefer to use a framework or a library that already packs a bunch of solutions to these recurrent head scratchers.
In regards to the advantages of dependency injection frameworks when doing unit testing is the idea that you don't need to test the dependencies of your class, but only your class.
For example, most likely your application has a layered design. It is very common to have a data access class or a repository that you use to retrieve data from a datasource. Logically, you also have a class where you use that DAO.
Evidently, you already wrote unit testing for your DAO, and therefore, when you're testing your business class (where the DAO is being used) you don't care about testing your DAO again.
Fortunately, since Spring requires some form of dependency injection for your DAO, this means your class must provide a constructor or a setter method through which we can inject that DAO into our business class, right?
Well, then during unit testing of your business class, you can conveniently use those injection points to inject your own fake DAO (i.e. a mock object). That way, you can focus on the testing of your business class and forget about retesting the DAO again.
Now compare this idea with other solutions you may have done on your own:
You inject the dependency directly by instantiating the DAO within your business class.
You use a static factory method within your code to gain access to the DAO.
You use a static method from a service locator within your code to gain access to the DAO.
None of these solutions would make your code easy to test because there is no simple manner to get in the way of choosing exactly what dependency I want injected into my business class while testing it (e.g. how do you change the static factory method to use a fake DAO for testing purposes?).
So, in Spring, using XML configuration or annotations, you can easily have different dependencies being injected into your service object based on a number of conditions. For example, you may have some configurations for testing that evidently would be different than those used in production. And if you have a staging environment, you may even have different XML configurations of dependencies for your application depending on whether it is running in production or integration environments.
This pluggability of dependencies is the key winning factor here in my opinion.
So, as I was saying, my suggestion to you is that you first expand your understanding of what problems Spring core (and in general all dependency injection frameworks) is trying to solve and why it matters, and that will give you a broader perspective and understanding of these problems in a way that you could to determine when it is a good idea to use Spring and when it is not.
I'm a newbie to Spring Framework and of course first thing comes to mind about spring is dependency injection. Now i could be wrong since i just started learning about Spring framework (esp. about dependency injection) but i think that dependency injection of beans to said objects is not meant for transaction data. Since the bean definition is for example defined in the spring.xml (a blue print) it is not meant for transactional data but rather for static and small amount of data. I don't see that there's any way to inject thousands of transactional objects into another object using dynamic XML (created during runtime).
So did i get this right? If that is so what's the real benefit of dependency injection?
There are several benefits from using dependency injection containers rather than having components satisfy their own dependencies. Some of these benefits are:
Reduced Dependencies
Reduced Dependency Carrying
More Reusable Code
More Testable Code
More Readable Code
These benefits are explained in more detail here.
You are right, transactional data (eg: data that represents a table row) don't normally be injected declaratively. Spring DI (dependency injection) commonly use to handle collaboration between multiple classes.
Common examples I've seen is along with DAO (data access object) and MVC (model view controller) pattern. In enterprise environment it's common to have a project with dozens or hundreds of database tables -- hence dozens / hundreds of DAO classes which get injected into controller classes.
If you don't use DI, you need to conciously manage which DAO should be created first, and which DAO should be injected into which controller etc. (this is a nightmare)
Code refactoring is (should) be a common thing as well. Business requirement always changes constantly. Without DI one simple refactoring could result in a massive and tricky untangling of 'which class depends on what and where'
Of all the articles I've read about the dependency injection, this is by far the best.
If you are using Spring for DI, I would suggest you read about #primary annotation. Spring makes it even easier to choose the implementation you want(from multiple implementations) for a given service. This article is good.
Dependency Injection and Inversion of Control change the control flow adding to a specific component the responsibility to manage de dependency graph and manage how it will be connected. The result is a great decoupling between dependant and dependency, improving the code maintainability, application reliability, and testability.
All websites state that the Spring core container is the basis for complete Spring framework i.e., it is used across
the all modules like AOP, JDBC module, Web module, etc. As per my understanding, the Spring core container's main purpose is
to inject dependencies, so avoiding the need of factory classes and methods. Is that correct?
Second question: When it is said, Spring core container is the basis for complete Spring framework (e.g., for Spring AOP). As per my understanding, in Spring AOP also, getting the object of classes like
ProxyFactoryBean is achieved by core container. Right?
Thirdly, it is stated that Spring core container avoids the need for programming the use of singletons. How come singleton
classes are avoided by core container?
yep
yep
All beans declared in Spring config files are singleton by default. They are instantiated when your application starts.
First off, your understanding of what you get from Spring is about right. So let's get on to your third question, the interesting one.
The key is it's not that you don't have singletons, it's that they're singletons by configuration. This is a vital difference, as it means you can avoid all the complicated singleton enforcement code (the source of frequent problems) and instead just write exceptionally simple programs that focus on the business end of things. This is particularly important when you are writing a program with non-trivial object lifetimes: for example, in a webapp it makes it very easy to manage the lifespan of objects that hold state associated with a user's session, since if the objects have session scope, they'll be “singleton per user session”. That's enormously easier to work with than many of the alternatives.
The fact that Spring can also help out with transactions is just perfect as transaction handling is distinctly non-trivial, and AOP is the best solution to them in Java that I've seen (other languages have other options open) with Spring supporting a pretty straight-forward way of doing it. Try to do it properly without if you don't believe me. Spring's pretty much wonderful.