Spring3中@Autowired注入的順序

一、問題

問題；Spring3中在Bean中多個屬性，多個方法@Autowired的順序是怎樣執行的？

Demo

@Component
public class MyBean {
	@Value("#{properties['security.token.default']}")
	private String expiretime;  //1

	public String getExpiretime() {
		return expiretime;
	}

	@Autowired
	public void setExpiretime(   //2
			@Value("#{bcmsmProperties['security.token.default']}") String expiretime) {
		this.expiretime = expiretime;
	}

	@Autowired
	public void init() { //3
		System.err.println("expiretime2:" + expiretime);
	}

}

是位置1 還是位置2 還是位置3先執行?

執行結果：

1.先執行位置1，屬性expiretime先被注入;

2.再到位置3 init（);

3.再到位置2 setExpiretime。

二、主要代碼

還是看Spring的源碼纔是硬道理。

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory

public void autowireBean(Object existingBean) {
		// Use non-singleton bean definition, to avoid registering bean as dependent bean.
		RootBeanDefinition bd = new RootBeanDefinition(ClassUtils.getUserClass(existingBean));
		bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
		BeanWrapper bw = new BeanWrapperImpl(existingBean);
		initBeanWrapper(bw);
		populateBean(bd.getBeanClass().getName(), bd, bw);
	}

protected void populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw) {
          .........
          boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
		boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

		if (hasInstAwareBpps || needsDepCheck) {
			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw);
			if (hasInstAwareBpps) {
				for (BeanPostProcessor bp : getBeanPostProcessors()) {
					if (bp instanceof InstantiationAwareBeanPostProcessor) {
						InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}

		applyPropertyValues(beanName, mbd, bw, pvs);
}	

接着調用org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor

  @Override
	public PropertyValues postProcessPropertyValues(
			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {

		InjectionMetadata metadata = findAutowiringMetadata(bean.getClass());
		try {
			metadata.inject(bean, beanName, pvs);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
		}
		return pvs;
	}
	
	
	
	
	private InjectionMetadata findAutowiringMetadata(Class<?> clazz) {
		// Quick check on the concurrent map first, with minimal locking.
		InjectionMetadata metadata = this.injectionMetadataCache.get(clazz);
		if (metadata == null) {
			synchronized (this.injectionMetadataCache) {
				metadata = this.injectionMetadataCache.get(clazz);
				if (metadata == null) {
					metadata = buildAutowiringMetadata(clazz);
					this.injectionMetadataCache.put(clazz, metadata);
				}
			}
		}
		return metadata;
	}
	
	
	private InjectionMetadata buildAutowiringMetadata(Class<?> clazz) {
		LinkedList<InjectionMetadata.InjectedElement> elements = new LinkedList<InjectionMetadata.InjectedElement>();
		Class<?> targetClass = clazz;

		do {
			LinkedList<InjectionMetadata.InjectedElement> currElements = new LinkedList<InjectionMetadata.InjectedElement>();
			for (Field field : targetClass.getDeclaredFields()) {
				Annotation annotation = findAutowiredAnnotation(field);
				if (annotation != null) {
					if (Modifier.isStatic(field.getModifiers())) {
						if (logger.isWarnEnabled()) {
							logger.warn("Autowired annotation is not supported on static fields: " + field);
						}
						continue;
					}
					boolean required = determineRequiredStatus(annotation);
					currElements.add(new AutowiredFieldElement(field, required));
				}
			}
			for (Method method : targetClass.getDeclaredMethods()) {
				Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
				Annotation annotation = BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod) ?
						findAutowiredAnnotation(bridgedMethod) : findAutowiredAnnotation(method);
				if (annotation != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) {
					if (Modifier.isStatic(method.getModifiers())) {
						if (logger.isWarnEnabled()) {
							logger.warn("Autowired annotation is not supported on static methods: " + method);
						}
						continue;
					}
					if (method.getParameterTypes().length == 0) {
						if (logger.isWarnEnabled()) {
							logger.warn("Autowired annotation should be used on methods with actual parameters: " + method);
						}
					}
					boolean required = determineRequiredStatus(annotation);
					PropertyDescriptor pd = BeanUtils.findPropertyForMethod(method);
					currElements.add(new AutowiredMethodElement(method, required, pd));
				}
			}
			elements.addAll(0, currElements);
			targetClass = targetClass.getSuperclass();
		}
		while (targetClass != null && targetClass != Object.class);

		return new InjectionMetadata(clazz, elements);
	}

三、分析

從紅色字體可以看到，在構造注入的MetaData對象時，是先構造屬性，再構造方法的;

循環的順序是依賴與class.getDeclaredFields()的順序 和class.getDeclaredMethods()的順序。

四、結論

1.@Autowired屬性的注入順序依賴於class.getDeclaredFields()的順序
2.@Autowired方法的注入順序依賴於class.getDeclaredMethods()的順序
3.@Autowired 屬性會優先生效於 @Autowired方法