How does Spring @Autowired work

Question

I came across an example of @Autowired

public class EmpManager {
   @Autowired
   private EmpDao empDao;
}

I was curious about how the empDao get sets since there are no setter methods and it is private.

Answer 1

Spring uses the CGLib API to provide autowired dependency injection.

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References

• Usage of CGLib forum comment by Rod Johnson
• 3.3.1. Injecting dependencies
• Pro Spring - Analyzing Spring Dependencies

Further Reading

• Introduction to the Spring Framework by Rod Johnson

Answer 2

Java allows you to interact with private members of a class via reflection.

Check out ReflectionTestUtils, which is very handy for writing unit tests.

Answer 3

Java allows access controls on a field or method to be turned off (yes, there's a security check to pass first) via the AccessibleObject.setAccessible() method which is part of the reflection framework (both Field and Method inherit from AccessibleObject). One the field can be discovered and written to, it's pretty trivial to do the rest of it; merely a Simple Matter Of Programming.