Spring lazy-init 懒加载的原理小结

package com.test.spring;

public class Coffee {

    public Coffee() {
        System.out.println("正在初始化bean !!!调用无参构造函数");
    }

}

<bean name="coffee" class="com.test.spring.Coffee"/>

@Test
public void testLazyInit() {

    System.out.println("开始初始化Spring容器 ");
    
    // 非懒加载的bean会在容器初始化时进行bean的初始化，后面会拿Spring启动时的源码进行分析
    ApplicationContext context = new ClassPathXmlApplicationContext("spring-beans.xml");
    
   // 非懒加载的bean 的构造函数会在这个位置打印
   System.out.println("Spring容器初始化完毕");

   System.out.println("开始从容器中获取Bean");

   Coffee coffee = context.getBean("coffee", Coffee.class);

   System.out.println("获取完毕  bean :" + coffee);
}

<bean name="coffee" class="com.test.spring.Coffee" lazy-init="true" />

@Test
public void testLazyInit() {

    System.out.println("开始初始化Spring容器 ");
    
    // 在初始化容器阶段不会对懒加载的bean进行初始化
    ApplicationContext context = new ClassPathXmlApplicationContext("spring-beans.xml");

    System.out.println("Spring容器初始化完毕");

    System.out.println("开始从容器中获取Bean");
    
    // 在这一阶段会对懒加载的bean进行初始化
    Coffee coffee = context.getBean("coffee", Coffee.class);

    System.out.println("获取完毕  bean :" + coffee);


}

ApplicationContext context = new ClassPathXmlApplicationContext("spring-beans.xml");

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
        throws BeansException {

    super(parent);
    setConfigLocations(configLocations);
    if (refresh) {
        // Spring ioc 启动入口 了解了refresh 就了解了ioc
        refresh();
    }
}

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        prepareRefresh();

        // Prepare the bean factory for use in this context.
        prepareBeanFactory(beanFactory);

        try {
            // Allows post-processing of the bean factory in context subclasses.
            postProcessBeanFactory(beanFactory);

            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);
            // Instantiate all remaining (non-lazy-init) singletons.
            // 初始化所有非 懒加载的bean！！！！
            finishBeanFactoryInitialization(beanFactory);

            // Last step: publish corresponding event.
            finishRefresh();
        }
 }

public void preInstantiateSingletons() throws BeansException {
   // 所有beanDefinition集合
   List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
   // 触发所有非懒加载单例bean的初始化
   for (String beanName : beanNames) {
       // 获取bean 定义
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
      // 判断是否是懒加载单例bean，如果是单例的并且不是懒加载的则在Spring 容器
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
          // 判断是否是FactoryBean
         if (isFactoryBean(beanName)) {
                final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                boolean isEagerInit;
                if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                   isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                      @Override
                      public Boolean run() {
                         return ((SmartFactoryBean<?>) factory).isEagerInit();
                      }
                   }, getAccessControlContext());
                }
         }else {
             // 如果是普通bean则进行初始化依赖注入，此 getBean(beanName)接下来触发的逻辑跟
             // context.getBean("beanName") 所触发的逻辑是一样的
            getBean(beanName);
         }
      }
   }
}

@Override
public Object getBean(String name) throws BeansException {   
    return doGetBean(name, null, null, false);
}

// 容器启动初始化 会初始化并依赖注入非懒加载的bean
ApplicationContext context = new ClassPathXmlApplicationContext("spring-beans.xml");

// lazy-init bean会进行第一次初始化并依赖注入  其他的会从缓存里取
Coffee coffee = context.getBean("coffee", Coffee.class);