What reasons might favor refusing dependency injection into beans via fields in Spring?

Refusal of dependency injection through fields (field injection) in Spring can be due to several reasons:

• Testability: Using constructor or setter injection makes it easier to create test instances of a class with mocks, as dependencies are explicitly passed through constructors or methods.

• Implicit dependencies: Field injection hides the class dependencies, making it harder to understand what the class depends on.

• Immutability: Constructor injection allows fields to be final, increasing code safety and predictability.

• Initialization order: With field injection, dependencies are set after the object is created, which can lead to errors if a dependency is used in the constructor.

Therefore, it is preferable to use constructor injection rather than field injection.