What is the difference between @Inject and @Autowired in Spring Framework? Which one to use under what condition?

Dependency Injection Exposed

@Inject originates from the Java CDI (Contexts and Dependency Injection) standard, also known as JSR-330. It's the "Java-universal" sign asking for dependency injection.

However, @Autowired is the Spring centric annotation, extending beyond @Inject its capabilities to @Qualifier, @Primary, and the much-coveted required attribute.

@Inject's Ideal Use-Cases:

✨ Wide Usability: Your application should remain portable across various DI frameworks.

🌿 Alignment with Standards: Configuration values from both Spring and non-Spring sources are in use.

@Autowired's Time to Shine:

💪 Rich Spring Features: Advanced features and the application of specialized Spring annotations are needed.

🎯 Complex Management: A multitude of bean instances or complex dependency management is needed.

@Autowired and @Inject - In Action

The Magic of Optional Dependencies

@Autowired defies the odds by handling missing beans without impeding context startup:

@Autowired: // "Ah, relax! Who needs dependencies all the time!" 😅

@Autowired(required=false)
private Optional<Dependency> dependency;


Lazy Injections with Provider<T>

@Inject gets one up with Provider, bringing you instances on demand:

@Inject: // "Stay lazy, you get it when you need it!" 😉

@Inject
private Provider<Dependency> dependencyProvider;


The Superiority of Specificity with Qualifiers

@Autowired takes your specificity to a new level when multiple implementations of an interface come into play, thanks to @Qualifier:

@Autowired: // "Look at me, I'm the captain now!" 🤠

@Autowired
@Qualifier("specificDependency")
private Dependency dependency;


Trading Off with @Inject and @Autowired

Every choice has its pros and cons:

@Inject's Edge:

• 💎 Standard Alignment: Promotes portability and interoperability.
• 🌐 Framework-Independent: Simplifies migration or polyglot management.

@Autowired's Advantage:

• 🛠️ Extensive Functionality: Taps into the wealth of the Spring framework.
• 🌀 Varied Dependency Management: Handles intricate injection scenarios, like optional dependencies and qualifiers.

The Co-existence of Java EE and Spring

With Java EE 6, @Inject was launched as a part of JSR-299 for CDI, which found support in Spring. However, with Spring 3.0 and higher versions, you get the best of Spring, served with a side of @Autowired, offering much-desired familiarity to Spring developers.