Constructor Injection vs Property Setter Injection ??

We need to set the record straight on this issue. There is ACTUALLY on such thing as Constructor Injection in Spring IOC framework  It is surprising that even Spring themselves use such anomalous terminology.

You have to admit that semantic precision dictates that the mechanism of declaring a component within a dependency context, by itself is not yet "injection". An injection occurs only when the contextual component is @Inject''ed (or the deprecated term @Autowired) into various sections of the code.

To be more precise, all the @Inject-able components need to have gone thro constructor enabled instantiation. Therefore, all cases are indeed constructor-instantiated-component injection.

The more precise phrasing is, component instantiation, where either

• Component instantiation thro constructor argument.
• Component instantiation thro null-argument constructor, in conjunction with property setter(s).
• Combination of both - Component instantiation thro constructor argument, in conjunction with property setter(s).

We could declare the scope of the component either as

• singleton
• prototype

And additional scopes for web/mvc

• request
• session 
• globalSession

We can then perform cascaded component declaration by using the ref keyword in place of values, to reference existing component declaration within the same context.

Injection then can be done thro two strategies

• @Inject annotated on setter method
• @Inject annotated directly on a field declaration.

The above clarification is demonstrated in a previous page that explains XML-based component declaration and injection .

But this argument becomes moot when we use Spring component annotation directly on the Java code of the bean itself.

Also, be reminded that using the @Autowired annotation should be avoided, but should use the Java standard @Inject annotation. They do the same thing, where @Autowired is Spring's terminology, whereas, @Inject is standard Java JSR 330.