Spring Bean Lifecycle

Introduction

Every Spring bean goes through a well-defined lifecycle: instantiation → dependency injection → initialization → use → destruction. Hooks like @PostConstruct, InitializingBean and @PreDestroy let you run setup and teardown logic.

Informative example

Lifecycle callbacks:

@Component
public class CacheWarmer {
    private final DataSource ds;

    @PostConstruct
    void warmCache() {
        log.info("Loading reference data...");
        // runs after DI, before bean is used
    }

    @PreDestroy
    void shutdown() {
        log.info("Flushing cache...");
        // runs on context shutdown
    }
}

// Bean scopes
@Scope("prototype")  // new instance every injection
@Scope("request")    // one per HTTP request (web apps)

Best practices

• Keep @PostConstruct logic fast — it blocks context startup.
• Use ApplicationListener for cross-cutting startup, not every bean.
• Default scope is singleton — understand implications for mutable state.

Purpose of this lesson

Master Spring Bean Lifecycle so you can apply it confidently in production Java code, technical interviews, and code reviews.

Step-by-step explanation

1. Understand the core idea behind Spring Bean Lifecycle.
2. Walk through the runnable example and tweak it in the playground.
3. Apply the pattern in a small Spring Boot or CLI exercise of your own.
4. Re-read the common mistakes and interview Q&A to lock the concept in.

Interactive workflow diagram

Debugging tips

• Bean not injected? Check component scan package — @SpringBootApplication only scans its package and below.

Optimization strategies

• Profile before optimizing — JFR (Java Flight Recorder) and async-profiler reveal real hotspots.
• Prefer immutable data and stream pipelines over hand-rolled loops when readability matters.
• Reach for the right JDK collection (ArrayList vs LinkedList vs ArrayDeque) before writing custom data structures.

Enterprise example

Teams at Netflix, Uber and Goldman Sachs apply Spring Bean Lifecycle daily — usually wrapped behind Spring Boot services with observability hooks (Micrometer + OpenTelemetry).

Interview questions & answers

Summary

In this lesson you learned Spring Bean Lifecycle — the concept, syntax, a runnable example, and the production pitfalls to avoid. Apply it in the playground before moving on.