Spring @Prototype 原理？

前置准备

1. 创建一个MyService类

java">@Scope("prototype")
@Service("myService")
public class MyService {
    public String getMessage() {
        return "Hello, World!";
    }
}

2. 创建一个main类，用于debug。
   

prototype 如何生效？

在context.getBean();方法中，有一个核心方法doGetBean()

java">protected <T> T doGetBean(
			String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
			throws BeansException {
			......省略
			try {
				// Create bean instance.
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args);
						}
						catch (BeansException ex) {
							// Explicitly remove instance from singleton cache: It might have been put there
							// eagerly by the creation process, to allow for circular reference resolution.
							// Also remove any beans that received a temporary reference to the bean.
							destroySingleton(beanName);
							throw ex;
						}
					});
					beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}

				else if (mbd.isPrototype()) {
					// It's a prototype -> create a new instance.
					Object prototypeInstance = null;
					try {
						beforePrototypeCreation(beanName);
						prototypeInstance = createBean(beanName, mbd, args);
					}
					finally {
						afterPrototypeCreation(beanName);
					}
					beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}

				....省略

		return adaptBeanInstance(name, beanInstance, requiredType);
	}

存在一个判断：else if (mbd.isPrototype()) 当bean definition的scope为prototype的时候调用createBean()将创建一个新的bean。