DefaultBeanFactory.java

package cn.javass.spring.chapter3;

import org.springframework.beans.factory.config.SingletonBeanRegistry;

public class DefaultBeanFactory {
   
    //Bean定义注册表
    private BeanDifinitionRegister DEFINITIONS = new BeanDifinitionRegister();
    
    //单例注册表
    private final SingletonBeanRegistry SINGLETONS = new SingletonBeanRegister();
    
    public Object getBean(String beanName) {
        //1.验证Bean定义是否存在
        if(!DEFINITIONS.containsBeanDefinition(beanName)) {
            throw new RuntimeException("不存在[" + beanName + "]Bean定义");
        }
        //2.获取Bean定义
        BeanDefinition bd = DEFINITIONS.getBeanDefinition(beanName);
        //3.是否该Bean定义是单例作用域
        if(bd.getScope() == BeanDefinition.SCOPE_SINGLETON) {
            //3.1 如果单例注册表包含Bean，则直接返回该Bean
            if(SINGLETONS.containsSingleton(beanName)) {
                return SINGLETONS.getSingleton(beanName);
            }
            //3.2单例注册表不包含该Bean，
            //则创建并注册到单例注册表，从而缓存
            SINGLETONS.registerSingleton(beanName, createBean(bd));
            return SINGLETONS.getSingleton(beanName);
        }
        //4.如果是原型Bean定义,则直接返回根据Bean定义创建的新Bean，每次都是新的，无缓存
        if(bd.getScope() == BeanDefinition.SCOPE_PROTOTYPE) {
            return createBean(bd);
        }
        //5.其他情况错误的Bean定义
        throw new RuntimeException("错误的Bean定义");
    }
    
   
    public void registerBeanDefinition(BeanDefinition bd) {
        DEFINITIONS.registerBeanDefinition(bd.getId(), bd);
    }
    
    private Object createBean(BeanDefinition bd) {
        //根据Bean定义创建Bean
        try {
            Class clazz = Class.forName(bd.getClazz());
            //通过反射使用无参数构造器创建Bean
            return clazz.getConstructor().newInstance();
        } catch (ClassNotFoundException e) {
            throw new RuntimeException("没有找到Bean[" + bd.getId() + "]类");
        } catch (Exception e) {
            throw new RuntimeException("创建Bean[" + bd.getId() + "]失败");
        }
    }
}