I'm fairly new to the the Spring and I'm trying to move our legacy code to spring.I'm trying to auto inject all the dependencies by using #Autowired.
My Bean has a factory method as follows:
public static Service getInstance(Registration registration) throws Exception {
Service service = null;
switch(registration.getType()) {
case XServer :
service = new XServer(); break;
case YServer :
service = new YServer(); break;
default :
service = new XServer(); break;
}
service.setRegistration(registration);
return service;
}
But when I use new in the factory method all the dependencies in the new class remains uninitialized. Also if I use appContext.getBean('beanname') it throws following exception:
Requested bean is currently in creation: Is there an unresolvable circular reference?
Can some one help me understand how to do it correct.
If I understand you right, then you are trying to instantiate the factory manually via the new command. But the Spring framework must register the beans, when you are trying to use them in the ApplicationContext. You have to create a Factory Bean which provides the creation of common other objects. These objects also have to be registered to the
Spring config of your application.
Have a look at the Spring documentation
That means you have to define somewhere in your application beans of following types: XServer, YServer and the type of your Factory Bean. Furthermore you should have a look at Method Injection, because you are trying to create beans with different scopes.
I've had a similar problem, but found this question helpful: Inject spring dependency in abstract super class.
It's not exactly the same, but it handles the point of inheritance. Note that it's using XML instead of annotations.
Related
I am migrating an EJB project to Spring boot project. I have successfully replaced other annotations to the spring annotation, but havving problem with SessionContext object.
My legacy code is bellow
#Resource
SessionContext sessionContext;
.....
if (some condition) {
sessionContext.setRollbackOnly();
return false;
}
For this code i am getting the following error
A component required a bean of type 'javax.ejb.SessionContext' that could not be found.
Action:
Consider defining a bean of type 'javax.ejb.SessionContext' in your configuration.
I think you'll have to use a few different functionalities.
setRollbackOnly()
Most often I have seen Session Context used for Rollbacks. In Spring, you can replace this with:
TransactionAspectSupport.currentTransactionStatus().setRollbackOnly();
or annotate class with
#Transactional(rollbackFor = MyException.class)
so you can throw your exception from class to cause rollback.
getBusinessObject()
The second most commonly used feature is method to load a business object so that I can, for example, create a new transaction within a same bean. In this case you can use Self-inject:
#Lazy private final AccountService self;
and annote method with #Transactional. This, of course, solves any other cases where you need to use the power of a proxy object.
Other functionality is provided by other classes in Spring, but I think that these two are the most commonly used in the Java EE world and when migrating, one will look to replace them in Spring.
Hi I have a spring boot application, which starts a spring integration flow, through a gateway interface, using Java DSL. Everything works fine on its own. I added AOP to capture exceptions, with #EnableAspectJAutoProxy(proxyTargetClass = true)
At this stage, it gives the error:
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'jobInitiator': Post-processing of
FactoryBean's singleton object failed; nested exception is
org.springframework.aop.framework.AopConfigException: Could not
generate CGLIB subclass of class [class com.sun.proxy.$Proxy54]:
Common causes of this problem include using a final class or a
non-visible class; nested exception is
java.lang.IllegalArgumentException: Cannot subclass final class class
com.sun.proxy.$Proxy54
When I remove the proxyTargetClass = true, it works but the advices are not triggered.
Any help? Is there a way to start the spring integration flow without a gateway?
There is no class associated with the gateway Proxy so you can't advise it.
Is there a way to start the spring integration flow without a gateway?
Instead of using the gateway, declare a bean of type MessagingTemplate and use template.sendAndReceive(someMessage) or template.convertSendAndReceive(somePojo) instead. See here.
(The gateway uses a MessagingTemplate internally; the gateway unwraps a MessagingException and throws the cause, the template does not).
It also does not support an error channel.
To get closer to the gateway functionality, you can subclass MessagingGatewaySupport and invoke its sendAndReceive() method(s).
I'm currently trying to configure Spring Boot (using Java Annotations and ComponentScan) for the following scenario:
Scenario
There's an interface MyService.
I want to provide a default implementation for MyService, let's call it MyDefaultService.
If the component scan detects no other implementation for MyService, Spring should instantiate MyDefaultService as a "fallback".
If there is a different implementation of MyService present, let's say MyCustomService, then that bean should always take precedence over MyDefaultService when autowiring a dependency to MyService. In that regard, MyDefaultService should be recessive (as opposed to #Primary).
Ideally, there should not need to be an additional annotation on MyCustomService to have it "override" MyDefaultService.
Ideally, no explicitly implemented factories or factory methods should be required.
Question
The question is: how do I need to annotate the MyDefaultService class in order to achieve this?
What I tried so far to solve the problem
Annotating MyDefaultService with #ConditionalOnMissingBean(MyService.class). Didn't work because MyDefaultService is never used, even if there is no other implementation of MyService.
There is an annotation called #Primarythat solves the problem. However, it needs to reside on MyCustomService, a class that I try to keep free of additional annotations. Essentially, I need the inverse annotation of #Primary on MyDefaultService. However, I couldn't find such an annotation.
Concrete use case
I am developing a service layer in one project, and a different project will implement a web UI layer on top of it. The UI project has a dependency to the service layer project. However, for certain functionalities implemented at the service layer, I need to know which user is currently logged in at the web context. So I have to define a service interface for that in the service layer project, such that it can be implemented by the UI project. However, for testing purposes in the service-layer project, I need a default implementation of that interface. Also, in case that the UI project team forgets to implement this interface, the app should not crash, but instead instantiate the fallback bean and issue a warning.
Thanks & kind regards,
Alan
I suggest writing an implementation of FactoryBean to do this. Your FactoryBean would scan the bean factory looking for beans that implement MyService, and if it finds one it returns that bean from getObject. If it doesn't, then it can instantiate MyDefaultService directly and return that. Your factory bean then gets annotated with #Primary.
So pieces like this (pseudo-code):
public class MyServiceFactory implements FactoryBean<MyService> {
ListableBeanFactory beanFactory;
public MyService getObject() {
Map beans = beanFactory.getBeansOfType(MyService.class)
if (beans.isEmpty())
return new MyDefaultService(); // plus args, obviously
else
return get_some_bean_from_the_map
}
}
and then
#Primary
#Bean
public MyServiceFactory MyServiceFactory() {
return new MyServiceFactory();
}
Spring will automatically handle the factory bean (i.e. it will make the MyService object available as a bean for injection like normal.
This solution doesn't require any special magic, and it's fairly obvious how it works. You can also handle errant cases such as multiple MyService beans being declared.
is it possible to inject spring beans into a polling filter class (FClass) controlled by a scheduler job?
i don't quite understand how singleton applies here.
i understand spring beans are singleton so in order to inject the spring beans into class FClass. i need to define FClass as a bean and add the DI as property etc..
so how do i know if FClass should be a singleton? i assume only classes that are singletons can be created and beans and have DI done to them.
my problem is :
i need to be able to inject my facade bean xfacade into FClass. x_facacde handles the dao object. it has Y_dao and a Z_hibernate session beans injected as DI.
when i tried to create a spring bean of StatusPollingFilter (FClass) and injected the facade bean - i got a null and the setter is never called for the injection in debug mode.
the problem:
i'm thought it might be something to do with the thread / scheduler nature of StatusPollingFilter, and since spring beans are singletons it might not work due to that.
i'm thinking of creating a factory for the StatusPollingFilter (FClass). but need to know if this is correct thing and i'm on right track before i do too much work and realize even that doesn't work as the problem might be somewhere else. ideally i just want to update a table in the easiest possible way. but i have to use hibernate as the DAO exists but hibernate is configured using
<bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
with /hibernate/TopoObject.hbm.xml
files.
so no matter how i try this i always get null pointer exception on session or injected facade bean.
reading some of the QA's here seems like because StatusPollingFilter is instantiated using the scheduler and not spring it cant be aware of the DI beans. so would the above factory pattern help here.
I may have an additional problem but i'll cross that bridge when i come to it. but just to mention briefly, in case anyone is aware of issues that i might hit ... not sure what / how the scheduler would invoke the factory for an instance as its all controlled by 3rd party api - which invokes a StatusPollingFilter but i'm assuming if i pass in the factory as the class and parameter it would find its way through... but initial part is the main question. please ignore the latter waffle. thanks in advance.
Actually :
i assume only classes that are singletons can be created
is where you are wrong.
A bean is just a class that you let spring instantiate. By default, they are created as singleton but you can specify the scope on your bean using the attribute scope (quite surprisingly). The value you can specify are those specified in the documentation here
So one thing you have to be careful with is the injection of beans scoped as prototype or request into singletons.
having read more - i have come across the ans.
because the StatusPollingFilter object is under control of scheduler (i knew that scheduler had something to do with it) then it is unaware of the spring beans which is why i keep getting null when i try injecting the bean.
i created a class:
ApplicationContextProvider implements ApplicationContextAware
added static access
private static ApplicationContext appContext;
did a setter for it :
public void setApplicationContext(ApplicationContext context)
{
appContext = context;
}
and added
public static Object getBean(String beanName) throws BeansException
{
return appContext.getBean(beanName);
}
used in code as :
EvoTAMDAOFacade evoDao = (EvoTAMDAOFacade) ApplicationContextProvider.getBean("evoDaoFacade");
i now have access to the facade bean and all injected beans into facade.
i still have an issue with hibernate session but thats prob due to some other issue.
pt here is i don't have access to the bean as its not in control of the spring container so i needed to somehow get it , probably could have done it via the factory method but why mess around when there a simpler way.
thanks for help by anyone who may have posted or tried to understand my problem.
I have several services implementing a common interface and I want to be able to choose one of them to inject into other services when my application starts up.
I have tried referencing the service implementation from resources.groovy as shown below but then Spring makes a new instance of the selected service and doesn't autowire its dependencies.
How can I get this solution to work? Or is there another way?
class MyService {
Repository repository
interface Repository {
void save(...)
}
}
class MySqlRepositoryService implements MyService.Repository { ... }
class FileRepositoryService implements MyService.Repository { ... }
resources.groovy:
beans = {
...
repository(FileRepositoryService) { }
}
It's of course possible to retrieve the reference to service from hand-built factory, but in my opinion, the approach you've taken is the best one. I use it myself, because it gathers all the information on configuration phase of the application in one place, so it's easier to track down which implementation is used.
The pitfall with autowiring that you've encountered can be explained very easily. All the classes put in grails-app/services are automatically configured by Grails as Spring singleton beans with autowiring by name. So the bean definition you've placed in grails-app/conf/resources.groovy creates another bean, but without the defaults imposed by Grails conventions.
The most straightforward solution is to put the implementation in src/groovy to avoid duplication of beans and use the following syntax to turn on the autowiring:
beans = {
repository(FileRepositoryService) { bean ->
bean.autowire = 'byName'
}
}