What's the best pattern for injecting a bean with arguments? - spring

Question

I have a number of cases in my app where client code wants to create a bean on-demand. In each case, the bean has 1 or 2 constructor arguments which are specified by the client method, and the rest are autowired.
Ex:
//client code
MyQuery createQuery() {
new MyQuery(getSession())
}
//bean class I want to create
//prototype scoped
class MyQuery {
PersistenceSession session
OtherBeanA a
OtherBeanB b
OtherBeanC c
}
I want A, B, and C to be autowired, but I have the requirement that 'session' has to be specified by the calling code. I want a factory interface like this:
interface QueryFactory {
MyQuery getObject(PersistenceSession session)
}
What's the most efficient way to wire up the factory? Is it possible to avoid writing a custom factory class that does new MyQuery(...)? Can ServiceLocatorFactoryBean be used for something like this?

Answer 1

You can use the #Autowired annotation on your other beans and then use the ApplicationContext to register the new bean. This assumes otherBeanA is an existing bean.
import org.springframework.beans.factory.annotation.Autowired
class MyQuery {
#Autowired
OtherBeanA otherBeanA
PersistenceSession persistenceSession
public MyQuery(PersistenceSession ps){
this.persistenceSession = ps
}
}
I'm not positive if this is the most efficient way to create a new bean, but it seems to be the best way at runtime.
import grails.util.Holders
import org.springframework.beans.factory.config.ConstructorArgumentValues
import org.springframework.beans.factory.support.GenericBeanDefinition
import org.springframework.beans.factory.support.AbstractBeanDefinition
import org.springframework.context.ApplicationContext
class MyQueryFactory {
private static final String BEAN_NAME = "myQuery"
static MyQuery registerBean(PersistenceSession ps) {
ApplicationContext ctx = Holders.getApplicationContext()
def gbd = new GenericBeanDefinition(
beanClass: ClientSpecific.MyQuery,
scope: AbstractBeanDefinition.SCOPE_PROTOTYPE,
autowireMode:AbstractBeanDefinition.AUTOWIRE_BY_NAME
)
def argumentValues = new ConstructorArgumentValues()
argumentValues.addGenericArgumentValue(ps)
gbd.setConstructorArgumentValues(argumentValues)
ctx.registerBeanDefinition(BEAN_NAME, gbd)
return ctx.getBean(BEAN_NAME)
}
}
Instead of using Holders, it's advised to use the ApplicationContext from dependecy inject if available, you could then pass this to the registerBean method.
static MyQuery registerBeanWithContext(PersistenceSession ps, ApplicationContext ctx) {
...
}
Calling class:
def grailsApplication
...
PersistenceSession ps = getRuntimePersistenceSession()
MyQueryFactory.registerBean(ps, grailsApplication.mainContext)
I changed the name of the method to truly reflect what it's doing - registering a spring bean as opposed to instantiating a MyQuery. I pass back the bean using the getBean method, but you also have access to the same bean using the ApplicationContext once it's been created.
def myQueryBean = MyQueryFactory.registerBean(ps)
// or somewhere other than where the factory is used
def grailsApplication
def myQueryBean = grailsApplication.mainContext.getBean('myQuery')