I'm using spring+scala 2.8. I have a #Transactional bean (marked with #Service), that is enabled in spring via < tx:annotation-driven / >, and when I fire up tomcat the controller that gets #Autowired with this service bean can't find an autowire candidate. I was beating myself up trying to figure out why it couldn't find a candidate object, when the #Service object was clearly getting instantiated (I could see this via log4j debug messages). I eventually decided to simplify by commenting out the < tx:annotation-driven / >, and voila! The webapp starts fine.
Can someone provide a technical reason why this doesn't work? I'm about to try #Qualifier to see if that "fixes" the problem.
When you add <tx:annotation-driven/> to your configuration, it causes various wrapping to happen with proxy classes (see the Spring documentation on transactions). This probably isn't playing well with the #Transactional annotation and Scala.
See Use Spring #Transactional in Scala
So I figured out my issue. It actually may have been "broken" with java as well as scala. My service class consisted only of an implementation class and no interface. Once #Transactional proxied the class spring was unable to find an autowire candidate. Simply adding an interface (or trait in scala) fixed the issue.
Related
I have picked up a project that uses #Autowired and dependency injection a lot. People have been saying all the nice things about them. It seems kind of like a magic.
I am new to Spring injection and #Autowired. My first glance of #Autowired is good, but when I work with them on Eclipse, I have difficulties tracing them around when debugging.
For example, is there an easy way in Eclipse that I can see where and how an #Autowired bean is initiated? How do I know if it is initiated correctly the way I want? Is there a way to trace the sequence of it being called/accessed?
Anybody has any tips or comments that may help me to debug #Autowired bean easier on Eclipse?
When a Spring application starts, it first creates instances of beans, either by scanning for annotations, or processing the XML Spring context definition. Some of those beans have to be created in a specific order, like if they use constructor injection. Once beans are created, wiring those beans together can happen.
If you want to see what happens when a bean is constructed, set a breakpoint in the constructors of the class. Look down the stacktrace to see what caused it to be constructed.
I'm experimenting with examples from this official Spring tutorials and there is a dependency on this code:
https://github.com/spring-guides/gs-async-method/tree/master/complete
If you look at the code on AppRunner.java class, I have 2 questions:
When server is starting, if I put a breakpoint in this class's constructor, seems like in the constructor, the GitHubLookupService is provided by spring, using the #Service bean that was configured. BUT, there was no #Autowired annotation on the constructor, so how in the world this constructor get called with the right dependency? It was supposed to be null.
Is it an automatic assumption of Spring Boot?
Does Spring see "private field + constructor argument, and it assumes it should look for an appropriate bean?
Is it Spring Framework or Spring boot?
Am I missing something?
As I remember, it was mendatory to provide default constructor to beans / service etc. How come this class (AppRunner) doesn't have a default constructor?
How does Spring knows that it should run the constructor with the argument?
Is it because it is the only constructor?
Starting with Spring 4.3, if a class, which is configured as a Spring bean, has only one constructor, the #Autowired annotation can be omitted and Spring will use that constructor and inject all necessary dependencies.
Regarding the default constructor: You either need the default constructor, a constructor with the #Autowired annotation when you have multiple constructors, or only one constructor in your class with or without the #Autowired annotation.
Read the #Autowired chapter from the official Spring documentation for more information.
Think of it this way... Suppose you have the following component:
#Component
public class FooService {
public FooService(Bar bar) { /*whatever*/ }
}
When Spring is scanning this class, it wants to know how it should go about constructing an instance. It's using reflection so it can get a list of all of the constructors at runtime.
In this case, it is completely unambiguous how Spring must construct this instance. There's only one constructor so there is no decision to be made, and no ambiguity at all.
If you add #Autowired here, you are not narrowing anything down, and you are not giving Spring any extra information to help make its decision - its decision is already made because there is only one candidate.
And so, as a convenience, the Spring team decided #Autowired should be optional. Since its not helping the Spring framework to make a decision, its presence is just noise.
If your component has multiple constructors then you can use #Autowired on one of them to tell Spring "use this one, not that one".
I am new Spring AOP and Aspectj. I have seen various posts related to injected bean in an aspect being null and I have run into a similar problem. I am still not clear how I should proceed to get past the problem I am currently encountering.
Issue: Currently we are using Spring 3.2.3 and all injection is through Annotation. In my case, the dependent bean is injected properly by Spring but at the point of execution the injected bean is NULL. BTW, this doesn't happen all the time but what I can say is the stack trace when it fails and when it succeeds is slightly different. When the injected bean is not null (I can successfully use the injected bean service), the call to the before advice (in the aspect) always happens before the target method is called as it should.When the injected bean is NULL, the call to the aspect is from the first statement of the target method. At this point, I think another aspect is instantiated and has no reference to the injected bean. Here is the aspect I have created:
#Component
#Aspect
public class Enable{
private NameService nameService;
#Autowired
public void SetNameService(NameSerice service){
// service is injected properly
this.nameSerice = service;
}
#Before("* *.*(..)")
public void callBefore(JoinPoint jp){
//sometimes nameService is null and sometimes it not not
this.nameService.lookup(...);
}
}
Examining the various posts, one way to get around this (as suggested in the post) is to configure the aspect in the XML configuration file and use the factory-method ="aspectOf" and in the configuration inject the reference to the NameService bean as a property. Our whole project uses Annotation based injection (as stated earlier). Assuming I can still configure the above aspect in an XML configuration file, how can I get the reference NameService bean Id so that I can add it to the configuration. I also saw a post related to using Configurable annotation but I assume that is for objects created outside the Spring IOC.
Currently, the aspects are woven using Aspectj compile option in pom.xml. Our root-context.xml contains the entry context:annotation-config and the aspect is injected into Spring IOC because component-scan is turned on for the folder where the aspect resides. Any help will be appreciated
This is well common error when use aspects in spring, you should add
<context:spring-configured/>
and
<aop:aspectj-autoproxy />
also add
#Configurable
#Aspect
public class Enable
To your appContext.xml
aspectOf is another style to do the above but I prefer use the nature of context.
It might be too late to answer this question. But i have come across the same situation and i fixed it as below.
1) Have a setter and getter for "NameService" in your aspect class.
2) Mark "NameService" with #Component ("nameService")
3) Configure "nameService" in xml configuration using setter injection.
4) Re-Start your server after making changes.
This should resolve the problem of getting null for "NameService" in aspect.
I have a test case which has a dependency of 'ticketDao', like below:
import javax.annotation.Resource;
import org.springframework.beans.factory.annotation.Qualifier;
public class LfnSaleCancellationIntegrationTest extends BaseIntegrationTest {
//#Resource(name = "baseTicketDao")
private BaseTicketDao ticketDao;
....
public void setTicketDao(#Qualifier("baseTicketDao") BaseTicketDao ticketDao) {
this.ticketDao = ticketDao;
}
}
and BaseIntegrationTest extends from spring test framework's AbstractJpaTests, Spring is v3.0.5
When run this test case, I got a similar exception:
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException:
No unique bean of type [com.mpos.lottery.te.gamespec.sale.dao.BaseTicketDao]
is defined: expected single matching bean but found 2:
[baseTicketDao, extraballTicketDao]
My project has evolved a long time, in fact when I encountered this exception at the first time, #Qualifier solved it. Till today this project has changed much, but I really have no idea why #Qaulifier and #Resource don't work any more.
And if i remove the dependency of 'ticketDao', the test case will pass. I am wondering whether there are some change of spring configuration cause this exception? or ... i have googled much, but seem no other people ever faced such a problem, pls give your comments, thanks very much!
You are using AbstractJPATests which is part of old spring test framework and (indirect) subclass of AbstractDependencyInjectionSpringContextTests. By default the injection is not annotation based but it discovers setters and fields and attempts injection by type. It would be recommended to switch to newer annotation based tests, refer to spring documentation for details.
As a workaround try to change autowire mode. Call it in test constructor as this.setAutowireMode(AutowireCapableBeanFactory.AUTOWIRE_BY_NAME), rename your field to baseTicketDao and remove setter.
I knew the reason. In my new project, there are a statement of context:component-scan in spring configuration file, which will register 4 BeanPostProcessors by default:
AutowiredAnnotationBeanPostProcessor(#Autowired)
RequiredAnnotationBeanPostProcessor(#Require)
CommonAnnotationBeanPostProcessor(JSR-250 annotations, #Resource, #PostConstruct etc, #WebServiceRef )
PersistenceAnnotationBeanPostProcessor(#PersistenceUnit and #PersistenceContext)
While in my old project, only the default BeanPostProcessor(internalAutoProxyCreator) has been registered. My understanding is AutowiredAnnotationBeanPostProcessor will always wire by type. Anyway if remove context:component-scan, my test case can pass now.
In fact i have migrate all my test cases to spring test context framework now, and context:component-scan must be stated, otherwise #Autowired, #Resource etc annotation will be ignored, and you will get a great many of NullPointerException of those automaticaly injected dependencies.
NOTE: <context:annotation-config/> will register those 4 BeanPostProcessors too.
This is a question to understand spring internals. There are a couple of workarounds suggested for self injection of a bean in spring because #Autowired doesn't work. Here are few threads. I would like to know the reason why and how does self injection work technically with #Resource annotation?
#Service(value = "someService")
public class UserService implements Service{
#Resource(name = "someService")
private Service self;
}
Any links to the spring source code would be appreciated. Thanks.
From another thread I got a response which seems fairly ok. Basically it states that spring specially adds defensive checks for handling #Autowired beans but #Resource beans bypass it and hence it works.
I don't know how exactly spring handles it, but here are a few options (the CDI specification uses these for example):
incomplete instances. When beans are instantiated and put in the context, their status is set as 'incomplete' - that is, their instance exists but their dependencies are not injected. Thus, first beans are instantiated, put in the context, and on the next stage their dependencies are injected. This makes the above case trivial - the container first create the instance and then, for each injection point, gets the desired bean from the context - itself, in this case
proxies. A proxy is created for each bean, so that it has beans without actually having instantiated the beans. It creates the proxies (by interface/concrete class), injects them into one another, and passes proxies around when needed. Finally each proxy gets its actual bean. This is perhaps not the case above, because this is used by CDI to handle circular constructor injection.