Spring核心学习（2）管理Bean的生命周期

前导：开始学习Spring核心思想，通过一个山寨精简版Spriing代码结合学习。

内容：1. 抽象BeanFactory-面向接口更易拓展BeanFactory-面向接口更易拓展。 2. 在AbstractBeanFactory内部初始化Bean。

这里的BeanDefinition相比上一个更加丰富，多了BeanDefinition包含的Bean的Class的信息，这里我们不在注册前就把Bean实例化给BeanDefinition，而是延迟到注册的时候才实例化Bean给BeanDefinition。

BeanDefinition：

package step2.core;

public class BeanDefinition {
	private Object bean;

	private Class beanClass;

	private String beanClassName;

	public BeanDefinition() {}

	public Object getBean() {
		return bean;
	}

	public void setBean(Object bean) {
		this.bean = bean;
	}

	public Class getBeanClass() {
		return beanClass;
	}

	public void setBeanClass(Class beanClass) {
		this.beanClass = beanClass;
	}

	public String getBeanClassName() {
		return beanClassName;
	}

	public void setBeanClassName(String beanClassName) {
		this.beanClassName = beanClassName;
		try {
			this.beanClass = Class.forName(beanClassName);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}

}

BeanFactory：

public interface BeanFactory {

	Object getBean(String name);

	void registerBeanDefinition(String name, BeanDefinition beanDefinition);
}

AbstractBeanFactory：

public abstract class AbstractBeanFactory implements BeanFactory{
	private Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>();

	@Override
	public Object getBean(String name) {
		return beanDefinitionMap.get(name).getBean();
	}

	@Override
	public void registerBeanDefinition(String name,
			BeanDefinition beanDefinition) {
		Object bean = doCreateBean(beanDefinition);
		beanDefinition.setBean(bean);
		beanDefinitionMap.put(name, beanDefinition);
	}

	/**
     * 初始化bean
     * @param beanDefinition
     * @return
     */
    protected abstract Object doCreateBean(BeanDefinition beanDefinition);
}

AutowireCapableBeanFactory：

public class AutowireCapableBeanFactory extends AbstractBeanFactory{

	@Override
	protected Object doCreateBean(BeanDefinition beanDefinition) {
		try {
			Object bean = beanDefinition.getBeanClass().newInstance();
			return bean;
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		}

		return null;
	}

}

public class HelloWorldService {

    public void helloWorld(){
        System.out.println("Hello World! from step2");
    }
}

public class BeanFactoryTest {

	@Test
	public void test() {
		// 1.初始化bean
		BeanFactory beanFactory = new AutowireCapableBeanFactory();

		// 2.注入bean
		BeanDefinition beanDefinition = new BeanDefinition();
		beanDefinition.setBeanClassName("step2.test.HelloWorldService");
		beanFactory.registerBeanDefinition("helloWorldService", beanDefinition);

		// 3.获取bean
		HelloWorldService helloWorldService = (HelloWorldService)beanFactory.getBean("helloWorldService");
		helloWorldService.helloWorld();
	}
}