I am being working with both Grails and Spring enterprise applications, I know the importance of Program for interface, but I seen most of Grails application are not following this mentioned design, rather their programming flow would be like controller -> service in the service layer they handle all the business and DB oriented things.
But when the same developer's programming style in Spring is emphasizing the importance of Program for interface
Why Grails don't following such design patterns, any reason?
By Program for interface I presume you mean program to an interface. This is a good practice whenever crossing a boundary that is significant to your design. The art is in deciding what is significant.
Using a framework does not force you into a particular pattern or architecture. The framework does change what is convenient. Some people get lured in by that convenience and lean heavily on the framework everywhere they can. Others rebel against this and think of it as lazy coding. In the end it's a trade off.
There has actually been considerable debate on this. I have previously summed that up here
Related
When we talk about spring (which ever module say jdbc), one of the reasons we use it is because it enables dependency injection and controls lifecycle of beans/classes. In programming, one of the most important fundamental is to code for interfaces rather than implementations, so today if I am using sql server driver v1, I can change it to v2 tomorrow if my code is written in such a way that it cares about Driver interface and not the implementations, then in what case would I ever need coding over configuration ?
The wording of your question seems a bit strange to me. Perhaps you are asking if there are any drawbacks to using Spring-like dependency injection. I can think of a few drawbacks, but whether these drawbacks outweigh the potential benefits of Spring is a matter of opinion.
Unfortunately, a Spring XML file is much more verbose than code to achieve similar (but hard-coded) initialisation of objects.
A programmer has to look not just at code but also at a Spring XML file to figure out what is going on. This, arguably, is a form of the Yo-yo problem.
One significant benefit of Spring is that it can be used to instantiate and configure any Java class (assuming the classes provide getters and setters). In particular, Java classes do not need to be polluted with the need to inherit from framework infrastructure classes. If you don't mind polluting classes with the need to inherit from framework infrastructure, then it is possible to have much more concise configuration files for instantiating and configuring objects. A case study illustrating this idea can be found in Chapters 9, 10 and 11 of the Config4* Practical Usage Guide. I am not proposing that the approach used in that case study be used for all applications, but I think it is a good approach to use when there is a complex, standardised API (such as for JMS) that is implemented by multiple products. In the case study, the approach results in a significantly easier-to-use API and eliminates some potential bugs from applications. Spring doesn't offer such benefits.
Section 9.4.2 of the Config4* Practical Usage Guide outlines a 9-step initialisation process for typical JMS applications. The framework library discussed in the case study ensures that those 9 steps are carried out in the correct order. It has been years since I looked at Spring so I might be wrong, but I don't think Spring has the flexibility to (easily or perhaps at all) enforce such a complex 9-step initialisation mechanism.
I was reading the question "Raw Servlet vs. Spring MVC" and was wondering if Spring MVC might slow down or blow up the memory consumption of your application compared with raw servlet?
Note: I originally asked it as a comment in the question mentioned above and was then kindly summoned to post it as a separate question.
Define "blow up". Define "slow down".
Of course memory usage will be higher, and of course performance will be lower.
How much higher, and lower compared to the additional functionality and flexibility Spring provides is the real question, and not knowing anything about the hypothetical app, it's impossible to say.
Building a testable, extensible, well-architected servlet-only app would involved re-implementing a lot of the functionality Spring provides. Which would you prefer to do--re-implement some (essentially) industry-standard code to the same degree it's been implemented and then write your app, or just write your app? And which would your boss prefer you do?
I m a newbie & i m good at Struts framework. Today i tried a tutorial for Spring MVC Framework.
The example url that i tried following is as below:
http://static.springsource.org/docs/Spring-MVC-step-by-step/part6.html
I think they have made this tutorial much more complex especially near its end. I saw some errors mainly typos in part 5, part 6 of tutorial. I found Spring framework as not properly organized and how would we know what classes to extend especially when their names are so weird (pardon my language) e.g. AbstractTransactionalDataSourceSpringContextTests.
Overall i found that Spring is making things much more complex than it should be. I'm surprised why there is such a hype about Springs being very easy to learn.
any suggestion how to learn spring easily ? how to judge what to extend ? is there a quick reference or something?
The tutorial you have referred to covers all the layers of the application - data access, business logic and web. For someone who is looking to only get a feel of Spring MVC, which addresses concerns specific to the web layer of the application, this could be more information than required. Probably that is why you got the feeling that the tutorial is complex.
To answer your questions, Spring is easy to learn because the whole framework is designed to work with POJOs, instead of relying on special interfaces, abstract classes or such. Developers can write software as normal Java applications - interfaces, classes and enums and use Spring to wire the components up, without having to go out of the way to achieve the wiring. The tutorial you have referred to tries to explain things in a little bit more detail than experienced programmers would typically do in a real application, probably because the authors wanted the readers to get enough insight into how Spring works so that concepts are understood well.
In most applications (regardless of their size or nature), there is typically no need to extend Spring classes or to implement specialised classes. The Spring community is quite large and an even larger ecosystem of readily available components exists that integrate with Spring. It is therefore very rare that one has to implement a Spring component to achieve something. For example, let us take the example of the data access layer. Different teams like using different approaches to accessing databases. Some like raw JDBC, others like third-party ORMs like iBatis or Hibernate while some others like JPA. Spring distributions contain classes to support all these approaches. Similarly, lets say someone was looking to incorporate declarative transaction management in their application. Again, transaction management can be done in many different ways and a large number of transaction management products are available for people to use. Spring integration is available for most of these products, allowing teams to simply choose which product they want to use and configure it in their Spring application.
Recent Spring releases have mostly done away with extensive XML based configuration files, which being external to the Java code did make Spring application a bit cumbersome to understand. Many things can be done nowadays with annotations. For example,
#Controller
public class AuthenticationController
{
...
}
Indicates that AuthenticationController is a web MVC controller class. There are even ways to avoid using the Controller annotation and follow a convention-over-configuration approach to simplify coding even further.
A good and simple tutorial to Spring MVC is available at http://www.vaannila.com/spring/spring-mvc-tutorial-1.html. This tutorial uses XML based configuration for Spring beans instead of annotations but the concepts remain the same.
I have seen tutorial you follow , Its seems you have follow wrong one first , you first tried to simple one, Instead of tutorials you should go for book first
I recommend you two books to understand the power of Spring
spring in action and spring recipes.
For practical you can use STS a special ide for spring project development.Its have some predefined template you dont't need to write whole configuration yourself.
In starting just see simple tutorials like Spring mvc hello world , form controller than go for big ones
Spring is very cool , All the best.
I love the concept of DI and loosely coupled system, a lot. However, I found tooling in Spring lacking at best. For example, it's hard to do "refactoring", e.g. to change a name of a bean declared in Spring. I'm new to Spring, so I would be missing something. There is no compiling time check etc.
My question is why do we want to use XML to store the configuration? IMO, the whole idea of Spring (IoC part) is to force certain creational pattern. In the world of gang-of-four patterns, design patterns are informative. Spring (and other DIs) on the other hand, provides very prescribed way how an application should be hooked up with individual components.
I have put Scala in the title as well as I'm learning it. How do you guys think to create a domain language (something like the actor library) for dependency ingestion. Writing the actual injection code in Scala itself, you get all the goodies and tooling that comes with it. Although application developers might as well bypass your framework, I would think it's relatively easy to standard, such as the main web site/app will only load components of certain pattern.
There's a good article on using Scala together with Spring and Hibernate here.
About your question: you actually can use annotations. It has some advantages. XML, in turn, is good beacause you don't need to recompile files, that contain your injection configs.
There is an ongoing debate if Scala needs DI. There are several ways to "do it yourself", but often this easy setup is sufficient:
//the class that needs injection
abstract class Foo {
val injectMe:String
def hello = println("Hello " + injectMe)
}
//The "binding module"
trait Binder {
def createFooInstance:Foo
}
object BinderImpl extends Binder {
trait FooInjector {
val injectMe = "DI!"
}
def createFooInstance:Foo = new Foo with FooInjector
}
//The client
val binder:Binder = getSomehowTheRightBinderImpl //one way would be a ServiceLoader
val foo = binder.createFooInstance
foo.hello
//--> Hello DI!
For other versions, look here for example.
I love the concept of DI and loosely
coupled system, a lot. However, I
found tooling in Spring lacking at
best. For example, it's hard to do
"refactoring", e.g. to change a name
of a bean declared in Spring. I'm new
to Spring, so I would be missing
something. There is no compiling time
check etc.
You need a smarter IDE. IntelliJ from JetBrains allows refactoring, renaming, etc. with full knowledge of your Spring configuration and your classes.
My question is why do we want to use
XML to store the configuration?
Why not? You have to put it somewhere. Now you have a choice: XML or annotations.
IMO,
the whole idea of Spring (IoC part) is
to force certain creational pattern.
In the world of gang-of-four patterns,
design patterns are informative.
ApplicationContext is nothing more than a big object factory/builder. That's a GoF pattern.
Spring (and other DIs) on the other
hand, provides very prescribed way how
an application should be hooked up
with individual components.
GoF is even more prescriptive: You have to build it into objects or externalize it into configuration. Spring externalizes it.
I have put Scala in the title as well
as I'm learning it. How do you guys
think to create a domain language
(something like the actor library) for
dependency ingestion.
You must mean "injection".
Writing the
actual injection code in Scala itself,
you get all the goodies and tooling
that comes with it.
Don't see what that will buy me over and above what Spring gives me now.
Although
application developers might as well
bypass your framework, I would think
it's relatively easy to standard, such
as the main web site/app will only
load components of certain pattern.
Sorry, I'm not buying your idea. I'd rather use Spring.
But there's no reason why you shouldn't try it and see if you can become more successful than Spring. Let us know how you do.
There are different approaches to DI in java, and not all of them are necessarily based on xml.
Spring
Spring provides a complete container implementation and integration with many services (transactions, jndi, persistence, datasources, mvc, scheduling,...) and can actually be better defined using java annotations.
Its popularity stems from the number of services that the platform integrates, other than DI (many people use it as an alternative to Java EE, which is actually following spring path starting from its 5 edition).
XML was the original choice for spring, because it was the de-facto java configuration standard when the framework came to be. Annotations is the popular choice right now.
As a personal aside, conceptually I'm not a huge fan of annotation-based DI, for me it creates a tight coupling of configuration and code, thus defeating the underlying original purpose of DI.
There are other DI implementation around that support alternative configuration declaration: AFAIK Google Guice is one of those allowing for programmatic configuration as well.
DI and Scala
There are alternative solutions for DI in scala, in addition to using the known java frameworks (which as far as I know integrate fairly well).
For me the most interesting that maintain a familiar approach to java is subcut.
It strikes a nice balance between google guice and one of the most well-known DI patterns allowed by the specific design of the scala language: the Cake Pattern. You can find many blog posts and videos about this pattern with a google search.
Another solution available in scala is using the Reader Monad, which is already an established pattern for dynamic configuration in Haskell and is explained fairly well in this video from NE Scala Symposium 2012 and in this video and related slides.
The latter choice goes with the warning that it involves a decent level of familiarity with the concept of Monads in general and in scala, and often aroused some debate around its conceptual complexity and practical usefulness. This related thread on the scala-debate ML can be quite useful to have a better grip on the subject.
i can't really comment on scala, but DI helps enforce loose coupling. It makes refactoring large apps soooo much easier. If you don't like a component, just swap it out. Need another implementation for a particular environment, easy just plug in a new component.
I agree! To me he way most people use Spring is a mild version of hell.
When you look at the standard Springified code there are interfaces everywhere, and you never really know what class is used to implement an interface. You have to look into some fantastic configuration to find that out. Easy read = not. To make this code surfable you need a very advanced IDE, like Intelly J.
How did we end up in this mess? I blame automated unit testing! If you want to connect mocks to each and every class you can not have dependencies. If it wasn't for unit testing we could probable do just as well without loose coupling, since we do not want the customer to replace single classes willy nilly in our Jars.
In Scala you can use patterns, like the "Cake Patten" to implement DI without a framework. You can also use structural typing to do this. The result is still messy compared to the original code.
Personally I think one should consider doing automated testing on modules instead of classes to escape this mess, and use DI to decouple entire modules. This strategy is by definition not unit testing. I think most of the logic lies in the actual connections between classes, so IMHO one will benefit more from module testing than unit testing.
I cannot agree that XML is problem in Java and Spring:
I use Spring and Java extensively without to much XML because most configuration is done with annotations (type and name is powerful contract) - it looks really nice. Only for 10% cases I use XML because it is easier to do it in XML than code special solution with factories / new classes / annotations. This approach was inspired by Guice and Spring from 3.0 implements its as JSR-330 (but even that I use Spring 2.5 with spring factory configured with JSR-330 annotations instead of default spring-specific #Autowired).
Probably scala can provide better syntax for developing in DI style and I'm looking at it now (pointed Cake Pattern).
We have started to use spring aop for cross cutting aspects of our application (security & caching at the moment).
My manager worries about the performance impact of this technology although he fully understands the benefits.
My question, did you encounter performance problems introduced by the use of aop (specifically spring aop)?
As long as you have control of your AOP I think it's efficient. We did have performance problems anyway, so by own reasoning we were not fully in control ;) This was mostly because it's important that anyone that writes aspects has full understanding of all the other aspects in the system and how they interrelate. If you start doing "smart" things you can outsmart yourself in a jiffy. Doing smart things in a large project with lots of people who only see small parts of the system can be very dangerous performance-wise. This advice probably applies without AOP too, but AOP lets you shoot yourself in the foot in some real elegant ways.
Spring also uses proxying for scope-manipluations and thats an area where it's easy to get undesired performance losses.
But given that you have control, the only real pain point with AOP is the effect on debugging.
If performance is going to be a concern, we have used AspectJ to great effect.
Because it uses bytecode weaving (compile time vs. runtime makes quite the difference) it's one of the fastest AOP frameworks out there. See: AOP Benchmarks
When I used it, I didn't - but then my application isn't your application.
If you use it for calls which are used in a very tight loop, there's the opportunity for a significant performance hit. If it's just used to check security once per request and cache various things, I can't see how it's likely to be significant - but that's why you should profile and benchmark your app.
I realise that "measure with your app" probably isn't the answer you were looking for, but it may well be the one you guessed you'd get :)
If you are using proxy-based AOP, you are talking about 1 additional Java method invocation per aspect applied. The performance impact there is pretty negligible. The only real concern is the creation of the proxies but this usually happens just once on application startup. The SpringSource blog has a great post on this:
http://blog.springsource.com/2007/07/19/debunking-myths-proxies-impact-performance/
In theory, if you use AOP do to what you could do with hard coupling, there is no performance issue, no overhead and no extra method calls unless you weave for nothing. AOP Framework offers you a way to remove the hard coupling and factorize your cross-cutting concern.
In practice, AOP Framework can introduce 3 types of overhead:
fire-time
interception mechanic
consumer integration (way to develop an advice)
For more details you can refer to when-is-aop-code-executed.
Just be careful how you implement an advice because transversal code is a temptation for boxing/unboxing and reflection (expensive in term of performance).
Without an AOP Framework (hard coupling your cross-cutting concerns) you can develop your presumed advices (dedicated for each treatment) easier without boxing/unboxing and reflection.
You have to know that most AOP Framework don't offer the way to avoid totally boxing/unboxing and reflection.
I developed one to respond to most of missing needs concentrated to 3 things :
user friendly (lightweight, easy to learn)
transparent (no breaking code to include)
efficient (no boxing/unboxing, no reflection in nominal user code and good interception mechanic)
You can find my open source project here : Puresharp API .net 4.5.2+ previously NConcern .NET AOP Framework
11 years after the question, look how degenerated this situation is.
Example: the vast majority think it is ok and normal to put a simple #Transactional spring java annotation to some method and let spring do the bridge between caller and callee proxied components. Now they have 20+ stackframes of undebuggable 'magic' code. The JIT compiler is rapidly exceeded and can no longer attempt inlining, or ends up bloating memory with tons of generated classes.
There is no limit to lazyness in this era of 'framework users'. No wonder e2e times for trivial http calls went from 100ms to 10 seconds. No wonder you need 2GB to run a lousy servlet container that used to run in 128MB. And don't get me started on the cost of logging exception stacktraces...
Have you ever thought about an AOP tools that adding aspects to object at runtime when you need? There is one for .net "Add Aspects to Object Using Dynamic Decorator" (http://www.codeproject.com/KB/architecture/aspectddecorator.aspx). I believe you can write a similiar one for Java.
If you are using some one framework for aspects there can be some performance issues .Next if you are creating abstraction above some one framework and aspects handling is done from framework then its very difficult to find out the cause of the problem relating to performance issues . If you are really concern about performance and small time slice concern more ,i suggest to write own aspects .No one want to reinvent the wheel but sometime for better it can be best.You can write own implementation of AOP alliance abstraction .
i have used spring AOP in a batch process in my current project to transaction manage a database.
At first, it was figured that there wouldn't be a performance problem, but we didn't figure into the equation that we called the database thousands of times. one aspect call in aop doesn't affect performance much, but multiply that by thousands, and it turns out the new system was worse than the old one, due to these extra method calls.
I'd say that aop is a great system to use, but try to take note on how many methods calls are added to your application