Generic getObjectType on FactoryBean should not be generic [SPR-5982] #10650
Description
Stephen Solka opened SPR-5982 and commented
The method signature for getObjectType on factoryBean is:
java.lang.Class<? extends T> getObjectType()
The problem with this is if you want to peg FactoryBean to a Generic class such as FactoryBean<List<String>> additional restrictions come on the implemtation of getObjectType. An example being:
Class<? extends List<String>> getObjectType()
{
return ?????;
}
return List.class; //compilation error
return (Class<? extends List<String>>) List.class; // compiles with eclipse compiler, compilation error with sun javac
List<String> myList = new ArrayList<String>();
return (Class<? extends List<String>>)myList.getClass(); //compiles on both javac + eclipse
What this means is to actually return something that can make it through compilation you have to have a instantiated object ahead of time to call getClass on. This is not the most ideal situation as per the javadoc "In the case of implementations that are creating a singleton object, this method should try to avoid singleton creation as far as possible; it should rather estimate the type in advance."
There is of course a work around (which is why I put this as minor) you can either not use FactoryBean generics or be sure to not peg a internal generic ex: FactoryBean<List>. I understand that changing such a important interface at this point is unrealistic but I would ask if the implementation is left as is, a note be added to the javadoc about how to work around this particular wart in the java generics implementation.
Affects: 3.0 GA
Issue Links:
- Generic return type on FactoryBean.getObjectType causes problems [SPR-6692] #11358 Generic return type on FactoryBean.getObjectType causes problems
2 votes, 3 watchers