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What is Spring?

Spring is a powerful, lightweight, open-source Java framework used to build enterprise-level applications. It simplifies Java development by providing built-in support for dependency management, database access, web applications, security, transactions, and microservices.

Why was Spring introduced?

Before Spring, developers mainly used Enterprise JavaBeans (EJB) for enterprise applications.

Problems with EJB:

• Complex configuration
• Heavyweight framework
• Difficult to test
• Required application servers

Spring solved these problems by providing:

• Lightweight architecture
• POJO (Plain Old Java Object) programming
• Easy testing
• Flexible configuration
• Better performance

Features of Spring
1. Lightweight

Spring is lightweight because it uses simple Java classes (POJOs).

2. Dependency Injection (DI)

Spring automatically creates and injects required objects instead of developers creating them manually.

3. Inversion of Control (IoC)

Normally, developers control object creation.

In Spring, the IoC Container creates and manages objects.

4. Loose Coupling

Objects depend on interfaces rather than concrete classes.

5. Aspect-Oriented Programming (AOP)

AOP separates common functionalities from business logic.

Examples:

• Logging
• Security
• Transaction management
• Exception handling

Instead of writing logging code in every method, Spring can apply it automatically.