spring-013: spring-boot-application-bean-lifecycle-comprehensive-execution-order-with-related-methods

1️⃣ Bootstrapping Phase (JVM & Spring Boot Startup)

1. JVM starts and loads the main class (public static void main(String[] args)).
2. SpringApplication.run() executes to initialize the application. 💡 Related method: SpringApplication.run()
3. Environment Setup:
   • Loads system properties, environment variables, application.properties/yml, and command-line arguments.
   • Determines active and default profiles. 💡 Related method: ConfigurableEnvironment#setActiveProfiles(), PropertySourcesPropertyResolver#getProperty()
4. Application Type Determined:
   • Web App → AnnotationConfigServletWebServerApplicationContext
   • Non-Web App → AnnotationConfigApplicationContext 💡 Related method: SpringApplication#determineWebApplicationType()
5. AutoConfiguration & SpringFactoriesLoader:
   • Automatically registers dependencies from the classpath (META-INF/spring.factories). 💡 Related method: SpringFactoriesLoader#loadFactoryNames()
6. SpringApplicationRunListeners Triggered:
   • Fires ApplicationStartingEvent, ApplicationEnvironmentPreparedEvent. 💡 Related method: SpringApplicationRunListeners#starting(), SpringApplicationRunListeners#environmentPrepared()

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2️⃣ Context Initialization & Bean Lifecycle

1. ApplicationContext is created and beans are scanned (@ComponentScan, @Configuration). 💡 Related method: AnnotationConfigApplicationContext#register()
2. Bean Definition is Loaded (Metadata Processing):
   • Spring reads bean definitions from configuration files (@Configuration), XML files, or component scanning (@Component).
   • This is a metadata processing step—no instances are created yet. 💡 Related method: BeanDefinitionRegistry#registerBeanDefinition()
3. Beans are instantiated (Object Creation):
   • Constructor-based instantiation.
   • Factory method instantiation. 💡 Related method: InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation()
4. Lifecycle Aware Beans are processed:
   • setBeanName() (BeanNameAware). 💡 Related method: BeanNameAware#setBeanName(String name)
   • setBeanClassLoader() (BeanClassLoaderAware). 💡 Related method: BeanClassLoaderAware#setBeanClassLoader(ClassLoader classLoader)
   • setBeanFactory() (BeanFactoryAware). 💡 Related method: BeanFactoryAware#setBeanFactory(BeanFactory factory)
   • setEnvironment() (EnvironmentAware). 💡 Related method: EnvironmentAware#setEnvironment(Environment environment)
   • setEmbeddedValueResolver() (EmbeddedValueResolverAware). 💡 Related method: EmbeddedValueResolverAware#setEmbeddedValueResolver(StringValueResolver resolver)
   • setResourceLoader(), setApplicationEventPublisher(), setMessageSource(), setApplicationContext(), setServletContext() (if applicable).
5. Conditional Beans & Profiles Applied (@Conditional, @Profile). 💡 Related method: Condition#matches(), ConfigurableEnvironment#getActiveProfiles()
6. Post-processing before initialization: 💡 Related method: BeanPostProcessor#postProcessBeforeInitialization()
7. Custom Initialization:
   • @PostConstruct
   • InitializingBean.afterPropertiesSet()
   • init-method (if defined in @Bean). 💡 Related method: InitializingBean#afterPropertiesSet(), @PostConstruct
8. Post-processing after initialization: 💡 Related method: BeanPostProcessor#postProcessAfterInitialization()

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3️⃣ Application Startup Completion

1. ApplicationContext Refreshes:
   • Dependency injection is completed.
   • Fires ContextRefreshedEvent. 💡 Related method: AbstractApplicationContext#refresh()
2. Embedded Web Server Starts (if applicable):
   • Tomcat, Jetty, or Undertow binds to a port.
   • ServletContextInitializer and WebApplicationInitializer execute for servlet-based apps. 💡 Related method: ConfigurableWebServerApplicationContext#start()
3. CommandLineRunner & ApplicationRunner Execute:
   • Runs post-startup logic. 💡 Related method: CommandLineRunner#run(), ApplicationRunner#run()
4. ApplicationReadyEvent Fires:
   • Application is fully initialized and ready to serve requests. 💡 Related method: ApplicationListener#onApplicationEvent(ApplicationReadyEvent)

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4️⃣ Bean Destruction & Application Shutdown

1. Graceful Shutdown Begins:
   • Controlled via spring.lifecycle.timeout-per-shutdown-phase. 💡 Related method: SpringApplication#setRegisterShutdownHook(true)
2. Pre-Destruction Processing: 💡 Related method: DestructionAwareBeanPostProcessor#postProcessBeforeDestruction()
3. Custom Cleanup:
   • DisposableBean.destroy().
   • @PreDestroy method.
   • Custom destroy-method (if defined in @Bean). 💡 Related method: DisposableBean#destroy(), @PreDestroy
4. ApplicationContext Closes:
   • Fires ContextClosedEvent. 💡 Related method: ConfigurableApplicationContext#close()
5. SpringApplication.exit() can be used to set custom exit codes (ExitCodeGenerator). 💡 Related method: SpringApplication#exit()

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5️⃣ Advanced Considerations (Optimizations & Monitoring)

✅ Lazy Initialization (@Lazy) – Beans are only created when accessed.

💡 Related method: DefaultListableBeanFactory#setAllowBeanDefinitionOverriding(false)

✅ Circular Dependency Handling – Use @Lazy, setter injection, or @DependsOn.

💡 Related method: AbstractAutowireCapableBeanFactory#doResolveDependency()

✅ FactoryBean Mechanism – Provides dynamic bean creation.

💡 Related method: FactoryBean#getObject()

✅ Spring Boot Actuator (if enabled):

• /actuator/health, /actuator/shutdown, /actuator/metrics. 💡 Related method: HealthIndicator#health() ✅ Performance Optimizations:
• Reduce startup time with spring.main.lazy-initialization=true.
• Tune garbage collection (-XX:+UseG1GC). ✅ Custom Application Listeners (ApplicationListener<>) – Hook into startup/shutdown events. 💡 Related method: ApplicationListener#onApplicationEvent()

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📌 Final Summary: Ultimate Execution Order

🟢 Bootstrapping: JVM → SpringApplication.run() → AutoConfiguration → Context Creation

🟠 Context Initialization: Beans Instantiated → Lifecycle Hooks → Dependency Injection

🔵 Application Startup: Web Server Starts → Runners Execute → Application Ready

🟣 Shutdown Phase: Pre-Destruction Callbacks → Cleanup → Context Closes

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