Spring核心学习（5）将Bean注入Bean-解析依赖

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

内容：1. BeanReference-保存Bean的引用。 2. getBean()中调用createBean()-lazy-init。这次我们用到了在Bean中注入Bean的情况，在这里我们再一次改写了AbstractBeanFactory，改写后的AbstractBeanFactory将多出一个List来保存所有注册的对象名，而且我们不再是注册时候就创建bean,并将beanDefinition的bean注入放到了具体的实现,实现懒加载，因为我们知道并不是注册后一定会用到这个bean，因此我们放到了getBean()的时候再实例化bean；AbstractBeanFactory中的preInstantiateSingletons()可以实现所有bean的初始化；AutowireCapableBeanFactory类要注意的地方是applyPropertyValues()这个函数，我们在这里要多出类中引用的注入。

BeanReference：

public class BeanReference {
	private String name;
	
	private Object bean;
	
	public BeanReference(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Object getBean() {
		return bean;
	}

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

BeanFactory：

public interface BeanFactory {
	
	Object getBean(String name) throws Exception;
	
	void registerBeanDefinition(String name, BeanDefinition beanDefinition) throws Exception;
}

AbstractBeanFactory：

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

	@Override
	public Object getBean(String name) throws Exception {
		BeanDefinition beanDefinition = beanDefinitionMap.get(name);
		if (beanDefinition == null) 
			throw new IllegalArgumentException("No bean named " + name + "is defined");
		Object bean = beanDefinition.getBean();
		if (bean == null) bean = doCreateBean(beanDefinition);
		return bean;
	}

	@Override
	public void registerBeanDefinition(String name,
			BeanDefinition beanDefinition) throws Exception{
		//TODO 这里不再是注册时候就创建bean,并将beanDefinition的bean注入放到了具体的实现,实现懒加载
		beanDefinitionMap.put(name, beanDefinition);
		beanDefinitionNames.add(name);
	}
	
	public void preInstantiateSingletons() throws Exception {
		for (Iterator<String> it = this.beanDefinitionNames.iterator(); it.hasNext();) {
			String beanName = (String) it.next();
			getBean(beanName);
		}
	}

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

AutowireCapableBeanFactory：

/**
 * 可自动装载内容的BeanFactory
 * @author acer
 *
 */
public class AutowireCapableBeanFactory extends AbstractBeanFactory{

	@Override
	protected Object doCreateBean(BeanDefinition beanDefinition) throws Exception{
		Object bean = createBeanInstance(beanDefinition);
		//notice,我们在这里要完成bean的注入
		beanDefinition.setBean(bean);
		applyPropertyValues(bean, beanDefinition);
		return bean;
	}

	protected Object createBeanInstance(BeanDefinition beanDefinition) throws Exception {
		return beanDefinition.getBeanClass().newInstance();
	}
	
	protected void applyPropertyValues(Object bean, BeanDefinition mbd) throws Exception {
		for (PropertyValue propertyValue : mbd.getPropertyValues().getPropertyValueList()) {
			Field declaredField = bean.getClass().getDeclaredField(propertyValue.getName());
			declaredField.setAccessible(true);
			Object value = propertyValue.getValue();
			if (value instanceof BeanReference) {
				BeanReference beanReference = (BeanReference) value;
				value = getBean(beanReference.getName());
			}
			declaredField.set(bean, value);
		}
	}
}