Spring Bean Lifecycle Explained

🚀 𝗦𝗽𝗿𝗶𝗻𝗴 𝗕𝗲𝗮𝗻 𝗟𝗶𝗳𝗲𝗰𝘆𝗰𝗹𝗲 — 𝗜𝗳 𝗬𝗼𝘂 𝗗𝗼𝗻’𝘁 𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱 𝗧𝗵𝗶𝘀, 𝗬𝗼𝘂’𝗿𝗲 𝗗𝗲𝗯𝘂𝗴𝗴𝗶𝗻𝗴 𝗕𝗹𝗶𝗻𝗱 Most developers use Spring daily… But can’t answer this: 👉 𝗪𝗵𝗮𝘁 𝗵𝗮𝗽𝗽𝗲𝗻𝘀 𝘁𝗼 𝗮 𝗯𝗲𝗮𝗻 𝗮𝗳𝘁𝗲𝗿 𝗶𝘁’𝘀 𝗰𝗿𝗲𝗮𝘁𝗲𝗱? 🧠 The Lifecycle: Creation → Injection → Initialization → Ready → Destruction That’s it. But each step matters. ⚙️ 𝗞𝗲𝘆 𝗦𝘁𝗮𝗴𝗲𝘀 𝗕𝗲𝗮𝗻 𝗗𝗲𝗳𝗶𝗻𝗶𝘁𝗶𝗼𝗻 𝗟𝗼𝗮𝗱𝗲𝗱: Spring reads the config and decides what beans need to be created 𝗕𝗲𝗮𝗻 𝗜𝗻𝘀𝘁𝗮𝗻𝘁𝗶𝗮𝘁𝗲𝗱: Object is created in memory (constructor runs) 𝗗𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝗰𝗶𝗲𝘀 𝗜𝗻𝗷𝗲𝗰𝘁𝗲𝗱: Required dependencies are wired into the bean 𝗕𝗲𝗮𝗻𝗣𝗼𝘀𝘁𝗣𝗿𝗼𝗰𝗲𝘀𝘀𝗼𝗿 (𝗕𝗲𝗳𝗼𝗿𝗲 𝗜𝗻𝗶𝘁): Custom logic runs before the bean is initialized 𝗜𝗻𝗶𝘁𝗶𝗮𝗹𝗶𝘇𝗮𝘁𝗶𝗼𝗻 (@𝗣𝗼𝘀𝘁𝗖𝗼𝗻𝘀𝘁𝗿𝘂𝗰𝘁 / 𝗶𝗻𝗶𝘁()): Final setup happens — bean becomes fully usable 𝗕𝗲𝗮𝗻𝗣𝗼𝘀𝘁𝗣𝗿𝗼𝗰𝗲𝘀𝘀𝗼𝗿 (𝗔𝗳𝘁𝗲𝗿 𝗜𝗻𝗶𝘁): Bean may be wrapped/modified (e.g., proxies, AOP) 𝗕𝗲𝗮𝗻 𝗥𝗲𝗮𝗱𝘆 𝘁𝗼 𝗨𝘀𝗲: Bean is now used by the application 𝗕𝗲𝗮𝗻 𝗗𝗲𝘀𝘁𝗿𝗼𝘆𝗲𝗱 (@𝗣𝗿𝗲𝗗𝗲𝘀𝘁𝗿𝗼𝘆 / 𝗱𝗲𝘀𝘁𝗿𝗼𝘆()): Cleanup happens — resources are released before shutdown 💣 𝗪𝗵𝗲𝗿𝗲 𝘁𝗵𝗶𝗻𝗴𝘀 𝗯𝗿𝗲𝗮𝗸 ❌ Using bean before initialization → NullPointerException ❌ Ignoring destroy phase → Memory leaks ⚠️ Hard Truth Field injection causes hidden issues Most devs don’t know when init runs Almost nobody handles cleanup properly If you don’t know the lifecycle stage your bean is in… 👉 You’re not debugging 👉 You’re guessing 𝗡𝗲𝘅𝘁 𝘁𝗶𝗺𝗲 𝘆𝗼𝘂𝗿 𝗮𝗽𝗽 𝗳𝗮𝗶𝗹𝘀 — Ask: “Which lifecycle stage broke?” That’s how real backend engineers think. #Java #BackendDeveloper #Hiring #ImmediateJoiner #ServingNoticePeriod #SpringBoot #JavaDeveloper

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