I am little new in Spring.
Having one question that did i need to annotate every class.
example: I have one controller and one is logic class. Controller autowired that class, So i need to annotate that class or not?
No you don't have to annotate all your classes with #Component you can but you don't have to. What you need to do is make your bean instance manage by Spring. You can do that in various ways.
(obviously) annotate the bean with #Component (or one of the specialized versions like #Service, #Controller etc.)
Write XML configuration and manually define your beans
Write Java configuration and use #Bean method to define your beans.
Either way will work.
Related
I have a simple Quarkus resource:
#Path("/rosters")
#Produces(MediaType.APPLICATION_JSON)
#Consumes(MediaType.APPLICATION_JSON)
public class RosterResource {
private final RosterService rosterService;
public RosterResource(RosterService rosterService){
this.rosterService = rosterService;
}
#GET
#Path("/{rosterId}")
public Response getRoster(#PathParam("rosterId")Long rosterId){
return Response.ok(rosterService.getRosterById(rosterId)).build();
}
}
I am trying to inject the RosterServiceinstance in my resource, but I am getting a javax.enterprise.inject.UnsatisfiedResolutionException. However, if I use the #ApplicationScoped annotation on RosterService, then everything works just fine. Is there a way of injecting the RosterService class in my resource without using annotations? In other words, is there a way of making RosterService discoverable by the Quarkus container without directly annotating the class?
Edit: looking into the CDI docs, it seems that you can manually register beans using a method with a #BuildStep annotation. However, it is not clear to me which class should contain the annotated method)
Another option would be to use a Jandex index
To the best of my knowledge, Quarkus only implements so called annotated bean discovery. That means that all CDI beans in Quarkus have to have a bean defining annotation. #ApplicationScoped is one of them.
EDIT: regarding a Jandex index, that allows you to scan for beans in additional JARs. In other words, it will only expand the set of classes that are scanned for a bean defining annotation.
When it comes to a #BuildStep method -- that is only possible in a Quarkus extension. Extensions are powerful (and indeed they can define additional beans) but also complex. You can start at https://quarkus.io/guides/building-my-first-extension, but it may feel overwhelming. It may also feel like this is not the right thing to do if you want to just make your class a bean -- and that would be true. But if your class comes from an external library that you can't change, extension makes sense.
Is there a specific reason why you don't want to annotate your service class with #ApplicationScoped (or any other of the bean discover/scope annotations)?
The only other way that I'm aware of (instead of annotations) is - as you yourself mentioned - the use of Jandex index.
I downloaded the spring-framework project, because I want to see how #Autowired is implemented.
So, I got to this file, which is an interface.
But when I want in Intellij to go to its implementation, no implementations are found.
So is this interface not implemented?
Then where is the code for #Autowired?
Well, this is not an interface it is actually an annotation.
In java #inteface is used to create an annotation.
Once the annotation is created, you can use that annotation on fields, classes, methods (based on what is specified in #Target of the annotation definition.
Spring does package scanning and finds all the things which are using a particular annotation and does the required processing.
Use this article to undestand more in How an annotation is created, used and the how the annotation processor finds and processes the annotation.
#Autowired doesn't really have much code, so to speak. It's just an annotation which is a Java type of interface that provides instructions to other parts of the codebase.
#Autowired is only an annotation or you can say a "marker". Spring use reflection to identify annotation and do something about that annotated thing. For example with #Autowired, when spring found it, spring will inject the annotated property with eligible bean.
I recently started exploring Spring Boot. I see that there are 2 ways to define Beans in Spring Boot.
Define #Bean in the class annotated with #SprinBootApplication
Define #Bean in a class annotated with #Configuration
I am also confused about stereo-type annotation #Repository #Service #Controller etc.
Can someone please explain how dependency-injection works with these annotations?
Yes it is possible.
Either you use #Bean in any of your #Configuration or #SpringBootApplication class or mark the bean classes explicitly with annotations like #Service, #Component #Repository etc.
#Service or #Component
When you mark a class with #Service or #Compoenent and if spring's annotation scanning scope allows it to reach to the package, spring will register the instances of those classes as spring beans.
You can provide the packages to be included/excluded during scan with #ComponentScan
#Bean
#Beans are marked on factory methods which can create an instance of a particular class.
#Bean
public Account getAccount(){
return new DailyAccount();
}
Now in you application you can simply #Autowire Account and spring will internally call its factory method getAccount, which in turn returns an instance of DailyAccount.
There is a simple difference of using #Bean vs #Service or #Compoenent.
The first one makes your beans loosely coupled to each other.
In the #Bean, you have flexibility to change the account implementation without even changing any of the account classes.
Consider if your classes instantiation is a multi-step operation like read properties values etc then you can easily do it in your #Bean method.
#Bean also helps if you don't have source code access to the class you are trying to instantiate.
Spring Boot auto-configuration attempts to automatically configure your Spring application based on the jar dependencies that you have added.
You need to opt-in to auto-configuration by adding the #EnableAutoConfiguration or #SpringBootApplication annotations to one of your #Configuration classes.
You are free to use any of the standard Spring Framework techniques to define your beans and their injected dependencies. For simplicity, we often find that using #ComponentScan (to find your beans) and using #Autowired (to do constructor injection) works well.
One way is to define #Bean in the class annotated with
#SprinBootApplication
If you see #SprinBootApplication it is combination of many annotation, and one of them is #Configuration. So when you define #Bean in the Main class, it means it's inside #Configuration class.
According to Configuration docs :
Indicates that a class declares one or more #Bean methods and may be
processed by the Spring container to generate bean definitions and
service requests for those beans at runtime.
class annotated with #Configuration
When you define #Bean is a class annotated with #Configuration class, it means it is the part of spring configuration all the Beans define in it all available for Dependency-Injection.
I have also seen some code where neither of the 2 above approaches
have been used and yet dependency injection works fine. I have tried
to research a lot on this but could not find any concrete answer to
this. Is this possible?
I am assuming you are talking about Sterio-type annotation. Every sterio type annotation has #Component, according to docs :
Indicates that an annotated class is a "component". Such classes are
considered as candidates for auto-detection when using
annotation-based configuration and classpath scanning.
#EnableBinding turns class into #Configuration, and it's documented that:
#RefreshScope works (technically) on an #Configuration class, but it might lead to surprising behaviour: e.g. it does not mean that all the #Beans defined in that class are themselves #RefreshScope. Specifically, anything that depends on those beans cannot rely on them being updated when a refresh is initiated, unless it is itself in #RefreshScope (in which it will be rebuilt on a refresh and its dependencies re-injected, at which point they will be re-initialized from the refreshed #Configuration).
So just a practical question: is there a way still to update some Receiver class annotated with #EnableBinding? I guess it would not be handled by the framework, and should be implemented with a custom #EventListener
For our simplest examples, we use the #Configuration classes where #EnableBinding is declared as the business logic beans themselves, which is made possible by the fact that #EnableBinding is a #Configuration and therefore a #Component. Since you don't need #EnableBinding on the Receiver bean itself, for example, I would separate the logic into a bean annotated with #RefreshScope. #EnableBinding itself is not subject to refresh, although the channels would be unbound/rebound on start/stop.
In Spring DI I love to use #Bean with factory method in #Configuration class instead of using #Component annotation explicitly. Is there a way to do the same with #Controller annotation for Spring Web? In another words, could I declare controller via factory method in some #Configuration class instead of explicit annotation?
Thats not possible since #Controller can only be placed on types. But more important are the methods. I assume you have multiple methods with #RequestMethod annotations. You can place as much methods as you like in this controller with differnet paths. Which should end up in around the same thing as you want?