Spring ek COMPREHENSIVE framework hai enterprise Java applications banane ke liye — dependency injection, transaction management, data access, web MVC, security, sab ek chhaте ke neeche. 2003 mein Rod Johnson ne banaya, EJB (Enterprise JavaBeans) ke complexity se frustrated hoke — Spring ka goal tha "plain old Java objects" (POJOs) se enterprise features milna, bina heavyweight boilerplate ke.

Spring ka core idea hai INVERSION OF CONTROL (IoC) — objects khud apni dependencies create NAHI karte, Spring container unhe CREATE karke INJECT karta hai. Isse code loosely-coupled, testable, aur maintainable banता hai. Spring ka ecosystem bahut bada hai — Spring Core, Spring MVC, Spring Data, Spring Security, Spring Boot, Spring Cloud — har ek specific problem solve karta hai.

// Bina Spring ke — manual object creation, tight coupling:
public class OrderService {
    private PaymentGateway gateway = new StripeGateway();  // hardcoded!
}

// Spring ke saath — dependency injected:
@Service
public class OrderService {
    private final PaymentGateway gateway;

    public OrderService(PaymentGateway gateway) {   // Spring inject karta hai
        this.gateway = gateway;
    }
}