Is the use of the @Autowired annotation mandatory to indicate that a dependency should be injected?

Using the @Autowired annotation in Spring is not the only way to indicate that a dependency should be injected. It is used for automatic wiring of components by type.

However, starting with Spring Framework 4.3, if a class has a single constructor, the @Autowired annotation on it can be omitted — Spring will automatically inject dependencies through that constructor.

Other ways to inject dependencies include:

• Through XML configuration
• Using the @Inject annotation (JSR-330)
• Through explicit bean creation and dependency passing

Thus, @Autowired is convenient and often used, but not mandatory in all cases.