If I have a class which uses a spring bean, (will be wired via #Autowired).
I noticed that not only the class that will be injected needs the #Component but also the class the uses it (inject it). Why is it like that? Should not spring inject wherever #Autowired is? Without having to use #Component for the injector class?
Spring processes and manages only those classes which are marked by one of stereotype annotations #Component, #Controller, #Repository, #Service.
It does not scan all of your classes (that would make the startup very slow).
If the class is not managed by Spring it does not process any of the annotation inside that particular class.
In Spring, one works with beans. A bean is a java object that is managed by a spring context. When encountering a bean containing an #Inject, Spring will seach its context for a bean of the type of the variable to be injected. If no such bean is defined, Spring will have nothing to inject. Also, if the class with the #Inject doesn't have a bean, then Spring won't know about it, and thus cannot inject anything into it.
To get Spring to create a bean of a class, several methods are available. Through annotations, the class has to be annotated with #Component, or the more specialized annotations #Service, #Repository and #Controller. Only then will Spring create a bean for the class that can be #Injected into other beans.
Related
I have a library that can use javax.inject annotations but must not be coupled to Spring, as it's used by both a Spring application and an application using Guice.
Other that creating an #Bean 'provider' in the #Configuration, is there a way to get Spring to inject the class into #Autowired/#Inject fields?
anyone of you do know which rule use when scan to instanced the spring beans defined with #component, #service or #repository, since when deploy an application into a environment spring instanced beans in one order and on other environment(with the same characteristics as the previous) the order is totally different, and because of this I get an error related to cyclic dependencies.
thanks,
sorin
How is it possible to define a Spring beans which need only #Autowired for defining new bean of certain type?
I have seen a solution, where service layer services are created without extra bean definitions for the new service. With bean definition I mean a line on config file specific to this service.
Is it possible to define beans so that certain package for example com.foo.bar.service.* become automatically defined with only adding #Autowired when calling it and not defining any other config per class in that package?
You might be able to write your own code that scans a Java package, and adds a bean for each of the classes found. That's not usually what is required, as many packages have helper classes that should not be exposed as beans.
But more likely, the beans will have one of the #Component, #Repository, #Service, #Controller annotations on them, and Spring will then register these as beans.
http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-scanning-filters
If I use #Service on a service class, do I need to make a service class bean in my servlet xml file or do I have to do both?
You don't have to declare a bean in your context file if you:
1) Annotate the class with:
#Component, #Service, #Controller or #Repository
2) Include the context:component-scan element in your context file like this:
<context:component-scan base-package="your.package" />
Hope that helps.
Last time I looked (Spring 2.5) #Service was a marker annotation subclassed from #Component, but with no additional behaviour. Which means that beans tagged with #Service become candidates for auto detection if you are using annotation-based configuration via classpath scanning.
As per the docs, the intention is that this annotation might include service layer specific functionality in future Spring releases. It can also act as an AOP point cut for all of your service layer components.
I am developing a GWT-Spring-Hibernate project and I want to use Spring Autowired annotation in GWT Service Servlet but my autowired annotated service is not injected. it is null. Is there a configuration detail that I missed?
I add
<context:annotation-config />
<context:component-scan base-package="com.org" />
to my ApplicationContext.xml and I have annotated my service as #Service("myService")
#Autowired
MyService myService; // This is null so WHY?
You need to "autowire" your RPC servlets during initialization. Take a look here http://code.google.com/p/gwt-spring-starter-app/
Well, the class where the #Autowired annotation resides should also be in the spring context (i.e. annotated with #Component), but I doubt it will work if it is a GWT (i.e. client-side) class.
Is class you're trying to inject your service into actually a bean declared in Spring context? It should be, auto-wiring won't work otherwise.
It can either be declared explicitly or, provided that it's somewhere within your "com.org" hierrarchy it will be detected automatically IF it's annotated as #Component or one of other stereotypes provided by Spring.