Spring @Prototype 原理？

前置准备

1. 创建一个MyService类

@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()

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。