Per Spring 3 document, The IoC container, the #Named annotation is a standard equivalent to the #Component annotation.
Since #Repository, #Service, and #Controller are all #Component, I tried to used #Named for all of them in my Spring MVC application. It works fine. But I found the replacement of #Controller seems to have a bug. In the controller class, originally, it was
#Controller
public class MyController{
...
}
It works fine. When I changed #Controller to #Named
#Named
public class MyController{
...
}
It failed with error:
"No mapping found for HTTP request with URI ...".
But if I added #RequestMapping to the class as follow
#Named
#RequestMapping
public class MyController{
...
}
It would work as expected.
For #Repository and #Service, I can simply replace them with #Named with no issue. But the replacement of #Controller needs extra work. Is there anything I am missing in the configuration?
#Named works the same as #Component. However, the annotations #Controller, #Service, and #Repository are more specific.
From the Spring docs:
#Component is a generic stereotype for any Spring-managed component.
#Repository, #Service, and #Controller are specializations of
#Component for more specific use cases, for example, in the
persistence, service, and presentation layers, respectively.
For example, these stereotype annotations make ideal targets for
pointcuts. It is also possible that #Repository, #Service, and
#Controller may carry additional semantics in future releases of the
Spring Framework. Thus, if you are choosing between using #Component
or #Service for your service layer, #Service is clearly the better
choice. Similarly, as stated above, #Repository is already supported
as a marker for automatic exception translation in your persistence
layer.
This section explains the difference with #Named.
Many components, like Spring's DispatcherServlet (MVC configuration in WebApplicationContext) aren't looking for Component, they are looking for #Controller. So when it scans your class, it won't find it in #Named. In a similar fashion, transaction management with #Transactional looks for #Service and #Repository, not for the more generic #Component.
All #Repository, #Service and #Controller are mainly for declaring Spring beans, apart from that it gives extra information to Spring about the type of bean like controller, dao etc
Related
Why we needs to use #service inside the service Implementation and #repository in the DAO Implementation. There are no problem occur when I interchange the #service and #repository annotation in the spring MVC.
According to documentaion #Repository,#Service,#Controller are all synonyms. They all are just specializations of #Component annotation. So, generally, they can be used one instead of other. But ... you should not do this.
First reason: any of these annotations make clear the role of your component in the application. Shows - is this component belongs to the controller, service, or data layer.
Second reason: some of these annotations processed differently by different Spring modules. For example, Spring Data JPA will process #Repository and will try to replace with implementation any interface marked by this annotation. Spring also will apply automatic exception translation to such classes. Another example: Spring Web MVC processes #Controller, and uses classes marked with it in URL mappings.
Actually, in future versions, some modules of Spring could process #Service in a particular way. Not as simple #Component. That's why documentation advises:
It is also possible that #Repository, #Service, and #Controller may
carry additional semantics in future releases of the Spring Framework.
Thus, if you are choosing between using #Component or #Service for
your service layer, #Service is clearly the better choice.
It depends on what you use for the remainder of the framework. In theory nothing changes as the #Service and #Repository annotations are basically #Component annotations. The same could be said for #Controller or #Endpoint (for Spring Ws and there are more).
However they express an intent of what a class is (a service, a repository) and makes it clear to the user to what layer that class belongs.
However if you also use Spring for transaction managemnt then #Repository is also a trigger for adding exception translation to that class (also see the reference guide).
Although nothing has to break it probably will at some point.
In my Spring application I have controllers with two annotations:
#Controller - Spring annotation
#AdminPanelController - my annotation
Is it possible change my annotation so I can used if with out the need to place #Controller in addition?
I want that Spring will process my annotation as #Controller annotation.
Your question is missing some detailed explanation on your needs, but my assumption is that you do not want to bother putting both your annotation and #Controller on your admin panel controllers. You want Spring-MVC you understand that any #AdminPanelController is-a #Controller.
This is exactly what #RestController annotation in Spring 4.0 any #RestController is-a #Controller (See the source code).
So your #AdminPanelController annotation should be similar to the one below
#Target(ElementType.TYPE)
#Retention(RetentionPolicy.RUNTIME)
#Documented
#Controller
public #interface AdminPanelController {
String value() default "";
}
So although java annotation does not support inheritance in the sense we expect (see Why is not possible to extend annotations in Java?) this will work for spring-mvc thanks to meta-annotation (I tested this with 4.1).
I'm reasonably sure that all you need is to annotate the AdminPanelController with #Controller
I have used, in my project, "springmvc-router" to remove #RequestMapping annotation from class definition.
Same way, is it possible to remove #Controller and #Service annotations in Class definitions?
Further, my package com.test.controllers include all contorllers annotated with #Controller and com.test.service.impl annotated with #Service.
Hence, can all classes under com.test.controllers be registered as controllers without #Controller?... The same follows for service annotation also.
Per Spring 3 document, The IoC container, the #Named annotation is a standard equivalent to the #Component annotation.
Since #Repository, #Service, and #Controller are all #Component, I tried to used #Named for all of them in my Spring MVC application. It works fine. But I found the replacement of #Controller seems to have a bug. In the controller class, originally, it was
#Controller
public class MyController{
...
}
It works fine. When I changed #Controller to #Named
#Named
public class MyController{
...
}
It failed with error:
"No mapping found for HTTP request with URI ...".
But if I added #RequestMapping to the class as follow
#Named
#RequestMapping
public class MyController{
...
}
It would work as expected.
For #Repository and #Service, I can simply replace them with #Named with no issue. But the replacement of #Controller needs extra work. Is there anything I am missing in the configuration?
#Named works the same as #Component. However, the annotations #Controller, #Service, and #Repository are more specific.
From the Spring docs:
#Component is a generic stereotype for any Spring-managed component.
#Repository, #Service, and #Controller are specializations of
#Component for more specific use cases, for example, in the
persistence, service, and presentation layers, respectively.
For example, these stereotype annotations make ideal targets for
pointcuts. It is also possible that #Repository, #Service, and
#Controller may carry additional semantics in future releases of the
Spring Framework. Thus, if you are choosing between using #Component
or #Service for your service layer, #Service is clearly the better
choice. Similarly, as stated above, #Repository is already supported
as a marker for automatic exception translation in your persistence
layer.
This section explains the difference with #Named.
Many components, like Spring's DispatcherServlet (MVC configuration in WebApplicationContext) aren't looking for Component, they are looking for #Controller. So when it scans your class, it won't find it in #Named. In a similar fashion, transaction management with #Transactional looks for #Service and #Repository, not for the more generic #Component.
All #Repository, #Service and #Controller are mainly for declaring Spring beans, apart from that it gives extra information to Spring about the type of bean like controller, dao etc
I came into IOC via Google Guice.
And now I've been forced to use Spring 2.5.6 at work & I am lost because Spring is quite complicated. Here are some questions after reading bits of the spring docs:
What is the difference between #Service, #Controller and #Component ? If I just want to auto wire my objects like Guice, do I need to be bothered by all these stereotypes ?
I'm planning to go the component-scan route with only constructor injection (Setter injection is mostly advocated by the Church of Scientology) and no freaking XML stuff. So is this code extract all I need ?
#Component
public class Foo
{
#Autowired(required=true)
public Foo( Bar bar, #Qualifier("yay") Boo yay,
#Qualifier("hoo") Boo hoo )
{
_bar = bar; _boo = boo;
}
Bar _bar;
Boo _boo;
....snipped...
}
#Component
#Qualifier("yay")
#Scope(BeanDefinition.SCOPE_PROTOTYPE)
public BooYay implements Boo
{
}
#Component
#Qualifier("hoo")
#Scope(BeanDefinition.SCOPE_PROTOTYPE)
public BooHoo implements Boo
{
}
In the above example, did I correctly qualify the 2 different implementations of Boo ?
Is there any feature similar to Google Guice's Providers ?
How do I mimic the #Singleton behaviour (in Guice) in Spring ?
Looking at your code, it seems all fine and your components will get autowired. You must give your package name in XML config file, so Spring can scan that for annotations.
Spring-managed components in general, the default and most common scope for autodetected components is singleton.
Actually, #Component is a generalisation of #Service and #Controller. See the docs.
Spring 2.5 introduces further
stereotype annotations: #Component,
#Service and #Controller. #Component
serves as a generic stereotype for any
Spring-managed component; whereas,
#Repository, #Service, and #Controller
serve as specializations of #Component
for more specific use cases (e.g., in
the persistence, service, and
presentation layers, respectively).
What this means is that you can
annotate your component classes with
#Component, but by annotating them
with #Repository, #Service, or
#Controller instead, your classes are
more properly suited for processing by
tools or associating with aspects. For
example, these stereotype annotations
make ideal targets for pointcuts. Of
course, it is also possible that
#Repository, #Service, and #Controller
may carry additional semantics in
future releases of the Spring
Framework. Thus, if you are making a
decision between using #Component or
#Service for your service layer,
#Service is clearly the better choice.
Similarly, as stated above,
#Repository is already supported as a
marker for automatic exception
translation in your persistence layer.
Make sure that your default-autowire or autowire value for those beans is byType. And then you should modify your Boo components like below,
#Component("yay")
#Scope(BeanDefinition.SCOPE_PROTOTYPE)
public BooYay implements Boo
{...}
#Component("hoo")
#Scope(BeanDefinition.SCOPE_PROTOTYPE)
public BooHoo implements Boo
{...}
You might like to do it with autowire = "byName", in that case you will not need #Qualifiers, but have to provide the matching setters. I hope you will managed to knock the thing off now.