When I annotate my Java service class, containing properties that are annotated with #Autowired, with Spring's #Service, booting the application results in an instance in which all properties are neatly wired.
If I also annotate the service class with #Validated (since I want method parameter validation) it results in a service bean in which all properties are null.
What am i doing wrong?
Related
Why do we need to use #Component annotation for Filter in spring boot, why we can't use #Configuration annotation.
Please note: I am not trying to register filter in FilterRegistrationBean.
#Configuration indicates that the class may contain #Bean methods and should be processed to define those beans in the application context. This isn't something that a Filter does so it should not be annotated with #Configuration.
If you look at the source for #Configuration, you'll see that it's annotated with #Component. #Configuration is a special kinds of #Component. In this case, all you need is for the Filter itself to be a bean. It doesn't have any #Bean methods so it's sufficient for it to be annotated with #Component. This will ensure that the Filter is a bean and Spring Boot will the register the Filter bean with the servlet container without any need for a FilterRegistrationBean and without wasting resources unnecessarily processing your Filter's class looking for #Bean methods.
I am learning Spring and Spring Boot.
In my Spring boot app, I am using #RestController annotation for one of my classes which receives requests and processes them accordingly.
#RestController
public class SampleController {
......
}
I want to ask would this class annotated with #RestController be a singleton class?
My thought is that this SampleController would also be a bean and since the default scope is Singleton,
it would be a Singleton class. I want to ask whether I am thinking right.
Yes, you are right. Any bean you creating via annotations #Component, #Service, #Repository, #Controller, #RestController and #Bean of course by default have Singleton scope. Check
Bean scope
In what order the #Component classes will be created in spring. is it #configuration annotated class that will be created first ?? Can we specify the order of creation ??
#Component and #Configuration are different types of annotations.
#Component and similar annotations (#Service, #Repository, etc. ) and its JSR-330 counterpart and allow you to declare beans that are to be picked up by autoscanning with <context:component-scan/> or #ComponentScan they register the bean definition for the classes, so they are roughly equivalent to declaring the specified beans with the <bean ... /> tag in XML. This bean types will adhere to the standard proxy creation policies.
#Configuration annotation was designed as the replacement of the XML configuration file. To create #Configuration annotated beans, Spring will always use CGLIB to subclass the #Configuration annotated class, overriding its #Bean annotated method to replace it with the bean lookup method to make singleton beans to be created only once. Despite that, #Configuration annotated classes are still able to use annotated(#Autowired, #Inject etc.) fields and properties to request beans (and even other #Configuration annotated beans too) from the container.
Now answer to your question, you have to annotate the class with #Configuration and then with #ComponentScan(basePackages = { "com.test.*" }) and you can't specify the order of creation.
In my spring context I am creating a service bean and a proxy for this service bean (explicitly). Both implement the same interface.
Can I ensure that autowiring cannot inject the target bean?
I would like to be able to use the target service with the #Resource or #Qualifier annotations, but when autowiring it should always be the proxy.
Any ideas?
Use the Primary annotation. It will indicate which bean should be use preferably when autowiring.
Hope this helps :)
You can put #Primary annotation in your proxy service like bellow:
#Primary
#Repository
public class ProxyOfSomeService implements SomeService
And after that when you use, #Autowired annotation on SomeService field, the ProxyOfSomeService will be injected by deafault.
But when you need the real service you can have it like bellow:
#Autowired
#Resource(name="someRealService")
private SomeService someService;
I think this serves your need, thanks!
Being fairly new to Spring I have a question about annotating a class. When annotating a class with #Component does this mean this class will be a Spring Bean and by default a singleton?
Yes, that is correct, #Component is a Spring bean and a Singleton.
If the class belongs to the service layer you may want to annotate it with #Service instead
But have in mind that in order for these annotations to be detected, you need to place this line in applicationContext.xml:
<context:component-scan base-package="com.yourcompany" />
About singletons - spring beans are all in singleton scope by default. The only thing you have to have in mind is that you should not store state in field variables (they should only hold dependencies). Thus your application will be thread-safe, and you won't require a new instance of a bean each time. In other words, your beans are stateless.
By default - Yes.
However, you can override this behavior using the #Scope annotation. For example: #Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)