What's the reason to instantiate Spring beans with factory methods?

Question

I know there are constructor-based injection and setter-based injection in Spring. When should I use factory methods to inject beans?

Answer 1

It's rather a design matter and depends on your architecture.

If you have classes with static factory methods, why should you add unnecessary constructors breaking the design just to fit a DI framework?

It's inflexible, thus Spring supports both ways.

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Excerpt from Joshua Bloch “Effective Java”:

Item 1: Consider static factory methods instead of constructors.

Static factory methods advantages:

• They have names.
• They are not required to create a new object each time they are invoked.
• They can return an object of any subtype of their return type.
• They reduce verbosity of creating parameterized type instances.

Static factory methods disadvantages:

• When providing only static factory methods, classes without public or protected constructors cannot be subclassed.
• They are not readily distinguishable from other static methods