IoC Container Source Code Analysis: Bean Instantiation an...

Overview

This article deeply explores the Spring IoC container initialization flow, analyzing Bean instantiation timing through breakpoint debugging.

Debug Test

The article answers the core question through breakpoint debugging: Is Bean creation during container initialization or during getBean?

Breakpoint 1: getBean

Setting a breakpoint at the getBean line and starting Debug mode, observation shows: When lazy loading is not configured, Bean creation is completed during container initialization.

Breakpoint 2: afterPropertiesSet

Setting a breakpoint at the afterPropertiesSet function of WzkBean, you can see that the constructor call timing is located in the finishBeanFactoryInitialization phase of the refresh method in the AbstractApplicationContext class.

Breakpoint 3: BeanFactoryPostProcessor

• Initialization location: AbstractApplicationContext.refresh() → invokeBeanFactoryPostProcessor(beanFactory)
• Call location: Same as above

Breakpoint 4: BeanPostProcessor

• Initialization: AbstractApplicationContext.refresh() → registerBeanPostProcessor(beanFactory)
• postProcessBeforeInitialization: During finishBeanFactoryInitialization(beanFactory) phase
• postProcessAfterInitialization: Same as above

IoC Container Initialization Main Flow

AbstractApplicationContext#refresh() method is the core:

@Override
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Refresh preprocessing
        prepareRefresh();

        // Get new BeanFactory instance, load BeanDefinition
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Set basic properties for BeanFactory
        prepareBeanFactory(beanFactory);

        try {
            // BeanFactory post-processing
            postProcessBeanFactory(beanFactory);

            // Invoke BeanFactoryPostProcessors
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register BeanPostProcessors
            registerBeanPostProcessors(beanFactory);

            // Initialize MessageSource
            initMessageSource();

            // Initialize event broadcaster
            initApplicationEventMulticaster();

            // Subclass refresh logic
            onRefresh();

            // Register listeners
            registerListeners();

            // Initialize all non-lazy-loading singleton Beans
            finishBeanFactoryInitialization(beanFactory);

            // Complete container refresh
            finishRefresh();
        }
    }
}

IoC Container Initialization Key Steps

Step	Description
1	Create container instance
2	Load Bean definitions (XML/annotations/Java config class)
3	Register Bean definitions
4	Process Bean dependency injection
5	Instantiate Beans
6	Initialize Beans (@PostConstruct, InitializingBean, custom init-method)
7	Register Bean post-processors
8	Activate Bean lifecycle
9	Complete container initialization

Bean Initialization Process

1. @PostConstruct annotated method executes
2. InitializingBean.afterPropertiesSet() is called
3. Custom initialization method is called
4. BeanPostProcessor.postProcessBeforeInitialization() executes
5. BeanPostProcessor.postProcessAfterInitialization() executes

Summary

The Spring IoC container completes initialization through the AbstractApplicationContext.refresh() method. The core is in the finishBeanFactoryInitialization(beanFactory) phase, which completes instantiation and initialization of all non-lazy-loading singleton Beans.