The Story of Spring Bean Injection: Do We Really Know Spring Beans Well

Many developers understand Spring Bean simply as something injected via @Autowired, but in real enterprise environments, it's important to know the sophisticated operating principles behind it. In particular, how beans are injected when @Primary and @Qualifier exist becomes the key to debugging and fixing errors.

Rather than simply relying on Google searches, one should directly explore the actual source code of Spring Framework to verify how it works. This is because search results are likely to contain outdated technical information due to backward compatibility.

This analysis focuses on the doResolveDependency() method of the DefaultListableBeanFactory class, digging into the process by which Bean Injection resolves dependencies, based on the source code.