Spring 使用简单Demo进行源码调试（七）

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2015/05/18/Spring 使用简单Demo进行源码调试（七）/

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接上篇日志Spring 使用简单Demo进行源码调试（六）继续。

经过前面几章详（gai）细（kuo）的调试，最后来到了Demo中的第二步，

Animal a = ctx.getBean("animal", Animal.class);// 创建bean的引用对象

展开getBean，代码如下。这一步通过getBeanFactory方法获取bean factory，然后使用bean factory获取对应的bean。

public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
		return getBeanFactory().getBean(name, requiredType);
	}

继续展开getBean。会走到之前初始化时候走到的方法,如下。由于已经初始化完毕，所以这一步走到Object sharedInstance = getSingleton(beanName);就会获取对应的bean实例。getSingleton这个函数的功能就是从已加载的实例中知道对应名称的bean实例，然后返回。接着代码进入if (sharedInstance != null && args == null)这个if中，通过getObjectForBeanInstance获取bean，这个函数说简单简单，简单的时候就是把前面获取的bean返回，说复杂复杂，前面获取的bean并不是需要的bean，而是一个factory的情况下，则使用这个factoy生成一个bean，然后返回。

protected <T> T doGetBean(
			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
			throws BeansException {

		final String beanName = transformedBeanName(name);
		Object bean;

		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			if (logger.isDebugEnabled()) {
				if (isSingletonCurrentlyInCreation(beanName)) {
					logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
							"' that is not fully initialized yet - a consequence of a circular reference");
				}
				else {
					logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
				}
			}
			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}

		else {
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			// Check if bean definition exists in this factory.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				if (args != null) {
					// Delegation to parent with explicit args.
					return (T) parentBeanFactory.getBean(nameToLookup, args);
				}
				else {
					// No args -> delegate to standard getBean method.
					return parentBeanFactory.getBean(nameToLookup, requiredType);
				}
			}

			if (!typeCheckOnly) {
				markBeanAsCreated(beanName);
			}

			try {
				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
				checkMergedBeanDefinition(mbd, beanName, args);

				// Guarantee initialization of beans that the current bean depends on.
				String[] dependsOn = mbd.getDependsOn();
				if (dependsOn != null) {
					for (String dependsOnBean : dependsOn) {
						getBean(dependsOnBean);
						registerDependentBean(dependsOnBean, beanName);
					}
				}

				// Create bean instance.
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
						public Object getObject() throws BeansException {
							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;
							}
						}
					});
					bean = 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);
					}
					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}

				else {
					String scopeName = mbd.getScope();
					final Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
					}
					try {
						Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
							public Object getObject() throws BeansException {
								beforePrototypeCreation(beanName);
								try {
									return createBean(beanName, mbd, args);
								}
								finally {
									afterPrototypeCreation(beanName);
								}
							}
						});
						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new BeanCreationException(beanName,
								"Scope '" + scopeName + "' is not active for the current thread; " +
								"consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
								ex);
					}
				}
			}
			catch (BeansException ex) {
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
		}

		// Check if required type matches the type of the actual bean instance.
		if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
			try {
				return getTypeConverter().convertIfNecessary(bean, requiredType);
			}
			catch (TypeMismatchException ex) {
				if (logger.isDebugEnabled()) {
					logger.debug("Failed to convert bean '" + name + "' to required type [" +
							ClassUtils.getQualifiedName(requiredType) + "]", ex);
				}
				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
			}
		}
		return (T) bean;
	}

	public boolean containsBean(String name) {
		String beanName = transformedBeanName(name);
		if (containsSingleton(beanName) || containsBeanDefinition(beanName)) {
			return (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(name));
		}
		// Not found -> check parent.
		BeanFactory parentBeanFactory = getParentBeanFactory();
		return (parentBeanFactory != null && parentBeanFactory.containsBean(originalBeanName(name)));
	}

	public boolean isSingleton(String name) throws NoSuchBeanDefinitionException {
		String beanName = transformedBeanName(name);

		Object beanInstance = getSingleton(beanName, false);
		if (beanInstance != null) {
			if (beanInstance instanceof FactoryBean) {
				return (BeanFactoryUtils.isFactoryDereference(name) || ((FactoryBean<?>) beanInstance).isSingleton());
			}
			else {
				return !BeanFactoryUtils.isFactoryDereference(name);
			}
		}
		else if (containsSingleton(beanName)) {
			return true;
		}

		else {
			// No singleton instance found -> check bean definition.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// No bean definition found in this factory -> delegate to parent.
				return parentBeanFactory.isSingleton(originalBeanName(name));
			}

			RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);

			// In case of FactoryBean, return singleton status of created object if not a dereference.
			if (mbd.isSingleton()) {
				if (isFactoryBean(beanName, mbd)) {
					if (BeanFactoryUtils.isFactoryDereference(name)) {
						return true;
					}
					FactoryBean<?> factoryBean = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
					return factoryBean.isSingleton();
				}
				else {
					return !BeanFactoryUtils.isFactoryDereference(name);
				}
			}
			else {
				return false;
			}
		}
	}

在获取了bean以后，就可以使用这个bean了。简单的demo的分析就到此了，还有很多的问题和不足，Spring作为一个强大的java框架，复杂程度难以想象，在每一步的处理中到包含了大量的错误处理等目前没有分析到的部分。