I've heard many times a "cyclic beans problem" in spring framework.
Could anyone describe when does it appear? I see 3 cases:
Bean A has autowired field of bean B, bean B has autowired field A. No constructors, no setters.
Both A and B has fields of each other. Bean A has a constructor with bean B there, bean B has has a constructor with bean A there (both constructors initialize the fields)
Both A and B has fields of each other. Bean A has a setter with bean B there, bean B has has a setter with bean A there (both setters initialize the fields)
Please, designate, which case has a problem? How to solve?
Related
I am trying to do conditional auto-wiring in Spring using annotation-based configuration. I have 2 different beans both implementing the same interface. I would like to do something like
if(some condition)
choose bean 1 to autowire
else
choose bean 2 to autowire
Is there a way to do this? I noticed the #Primary and #Qualifier annotations, but they will only choose one bean or the other to autowire and not based on some condition. Thanks.
Autowiring injects a bean into the target bean only once, when the target object is being initialized. Afterwards it remain unchanged.
Consider other approaches. For instance, inject both beans and implement a method that selects one of these beans depending on your conditions.
A,B C, And when i am using setter injection for All , And one bean reference to each other. then what will be sequence of bean for object creation.
And when i am using constructor injection for all and A have B reference B have c reference and c have a reference then what will be the sequence for object creation?.
I have declared following list using spring util namespace in my spring configuration file:
<util:list id="childList">
<ref bean="child1"/>
<ref bean="child2"/>
<ref bean="child3"/>
</util:list>
where all reference bean are marked with #Componant annotation and their respective beans are creating. But whenever I am trying to Autowired any beans property like:
#Component
public class ListTest{
#Autowired
#Qualifier("childList")
private List<IParent> list;
public List<IParent> getList() {
return list;
}
}
Gives exception as: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'listTest': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private java.util.List com.spring3.componentScanFilterTest.ListTest.list; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.spring3.componentScanFilterTest.IParent] found for dependency [collection of com.spring3.componentScanFilterTest.IParent]: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true), #org.springframework.beans.factory.annotation.Qualifier(value=childList)}
But instead of #Autowired and #Qualifier if I use as:
#Resource(name="childList")
It works. Why? As per my understanding #Autowired is used to autowire the property matching by type and #Qualifier is used to select any one bean from multiple ambiguous beans.
Please explain.
Spring docs says.
As a specific consequence of this semantic difference, beans that are themselves defined as a collection or map type cannot injected through #Autowired, because type matching is not properly applicable to them. Use #Resource for such beans, referring to the specific collection or map bean by unique name.
Hope this clear your doubt.
Type matching is not properly applicable to beans which defined as collection.
If you intend to express annotation-driven injection by name, do not primarily use #Autowired - even if is technically capable of referring to a bean name through #Qualifier values. Instead, prefer the JSR-250 #Resource annotation which is semantically defined to identify a specific target component by its unique name, with the declared type being irrelevant for the matching process.
As a specific consequence of this semantic difference, beans which are themselves defined as a collection or map type cannot be injected via #Autowired since type matching is not properly applicable to them. Use #Resource for such beans, referring to the specific collection/map bean by unique name.
Here:
http://docs.spring.io/spring/docs/2.5.x/reference/beans.html#beans-autowired-annotation-qualifiers
You are trying to get list of all beans of type Parent that have the qualifier "childList".
I am injecting a spring-managed bean into an abstract class and it seems that it doesn't work. Here is an explanation of what I do, if it is not enough, I can edit the post and add some code:
implement the java code - 1 abstract class, 2 classes that inherit from it and the bean to be injected and used in the abstract class and thus by the subclasses.
define the bean in the spring config.
define the abstract class and 2 subclasses in the spring config.
define the first bean as a property of the abstract class bean.
result - it's not working.
Then I tried to move the injected bean from the abstract class into the two subclasses. Now it works.
So, did I do something wrong, or is it theoretically impossible to inject a bean into an abstract class with spring 3 and Java EE 5?
Is it theoretically impossible to inject a bean into an abstract class with spring 3 and Java EE 5?
Dependency Injection happens on an Object not its Class. Spring injects dependencies into managed beans which are Objects already instantiated by Spring. Since, an Abstract Class cannot be instantiated it would be conceptually wrong to think about DI here.
On a somewhat related note, you can also define a non-abstract Class as an abstract Spring bean by adding the attribute abstract=true to the <bean> tag. This indicates that the bean would not be instantiated and would serve as a mere template of properties that other beans can use through bean inheritance (which isn't related to Java inheritance at all).
In this context as well, (if you've configured it) the Dependency Injection would only happen for the child beans and not their parent bean since it has been defined as abstract. (Note: It's not mandatory for the parent bean to be abstract but it makes sense to do so when all it does is to act as a set of common bean properties.)
I am trying to create a bean and than trying to inject the same in my Controller but i am getting bean creation failure error.Here is my code
#Service("springSecurityLoginServiceImpl")
public class SpringSecurityLoginServiceImpl implements SpringSecurityLoginService
{
//impl
}
this is how i am trying to inject it in my controller
#Controller
#RequestMapping("springSecurity/login.json")
public class SpringSecurityLoginController
{
#Autowired
#Qualifier("springSecurityLoginServiceImpl")
SpringSecurityLoginService springSecurityLoginService;
}
There is no entry in Spring-MVC-config xml file except these annotation, but when i am starting server facing the following exception
org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping#0'
defined in ServletContext resource [/WEB-INF/config/spring-mvc-config.xml]:
Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'springSecurityLoginController':
Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException:
Could not autowire field: com.core.servicelayer.user.SpringSecurityLoginService com.storefront.controllers.pages.SpringSecurityLoginController.springSecurityLoginService;
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException:
No matching bean of type [com.core.servicelayer.user.SpringSecurityLoginService] found for dependency:
expected at least 1 bean which qualifies as autowire candidate for this dependency.
Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true),
#org.springframework.beans.factory.annotation.Qualifier(value=springSecurityLoginServiceImpl)}
i am not sure what i am doing wrong or what extra i have to do
SpringSecurityLoginController class refers SpringSecurityLoginService class, for which a bean isn't defined. That much the error says.
It is true, because you've only defined a bean for the class LoginServiceImpl, which doesn't seem to extend SpringSecurityLoginService in any way.
Spring's bean lookup algorithm first searches for beans of which type is, or extends, SpringSecurityLoginService. Then, it narrows the avaialble options using the Qualifier. In this case, no bean is found in the first place...
See Spring doc:
4.11.3 Fine-tuning annotation-based autowiring with qualifiers
Since autowiring by type may lead to multiple candidates, it is often
necessary to have more control over the selection process. One way to
accomplish this is with Spring's #Qualifier annotation. This allows
for associating qualifier values with specific arguments, narrowing
the set of type matches so that a specific bean is chosen for each
argument.
You need that LoginServiceImpl will implement SpringSecurityLoginService, for instance.
EDIT
Since it was just a typo you might be not including SpringSecurityLoginService's package in component-scan tag, in your spring configuration file (as gkamal has already mentioned). You should have there something like:
<context:component-scan base-package="org.example"/>
where org.example should be replaced by SpringSecurityLoginService's package.