I just start to study Spring and I have a question:
In order to inject a bean, when is it better to use property-based dependency injection:
<bean id="myFirstClass" class="..."> <property name="targetProperty"> <bean id="TheBeanIwantToInject" class="..."/> </property> </bean> instead of constructor-based dependency injection
<bean id="myFirstClass" class="..."> <constructor-arg ref="TheBeanIwantToInject"/> </bean> or it's just two equivalent solutions?
If you want to create immutable objects then the constructor-arg variant is the only option. I prefer that one.
if you have bidirectional dependencies you will need one of them to be property injected. usually though you should think about your architecture if you have such a case. the interdependency could be extracted in a new class for example
You need to honestly look at what you are doing in the code and what makes sense. From a pure OO perspective, if you need the dependency for your class to work and it should never be changed, used constructor injection. If you need a default dependency but it might change (or an optional one), use properties.
This is a holy war type question however. Should I use XML or Autowire, should I inject via properties or constructor. The real key is be consistent. If you are consistent, it will make sense to the next poor developer that has to work in your code even if it isn't technically correct according to OO principles. If you are inconsistent, I feel sorry for the next guy.
My preferences, not that it matters, is to use constructor injection as much as possible, it allows me to have cleaner code without all the getters and setters that may break encapsulation logic.
