获取Bean实例

getObjectForBeanInstance

protected Object getObjectForBeanInstance(
			Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {

		// Don't let calling code try to dereference the factory if the bean isn't a factory.
		//如果bean名称是以&开头的,默认是FactoryBean对象
		if (BeanFactoryUtils.isFactoryDereference(name)) {
			if (beanInstance instanceof NullBean) {
				return beanInstance;
			}
			if (!(beanInstance instanceof FactoryBean)) {
         //&开头的如果不是NullBean
				throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass());
			}
			if (mbd != null) {
       //
				mbd.isFactoryBean = true;
			}
			return beanInstance;
		}

// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
//bean名称不是&开头的,并且不是FactoryBean类型的直接返回bean实例		
if (!(beanInstance instanceof FactoryBean)) {
			return beanInstance;
		}

		Object object = null;
		if (mbd != null) {
			mbd.isFactoryBean = true;
		}
		else {
     //从缓存中,获取FactoryBean实例化的bean
			object = getCachedObjectForFactoryBean(beanName);
		}
		if (object == null) {
			// Return bean instance from factory.
			FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
			// Caches object obtained from FactoryBean if it is a singleton.
			if (mbd == null && containsBeanDefinition(beanName)) {
				mbd = getMergedLocalBeanDefinition(beanName);
			}
			boolean synthetic = (mbd != null && mbd.isSynthetic());
      //通过FactoryBean来实例化bean
			object = getObjectFromFactoryBean(factory, beanName, !synthetic);
		}
		return object;
	}

/**
	 * Used to dereference a {@link FactoryBean} instance and distinguish it from
	 * beans <i>created</i> by the FactoryBean. For example, if the bean named
	 * {@code myJndiObject} is a FactoryBean, getting {@code &myJndiObject}
	 * will return the factory, not the instance returned by the factory.
	 */
	String FACTORY_BEAN_PREFIX = "&";

public static boolean isFactoryDereference(@Nullable String name) {
		return (name != null && name.startsWith(BeanFactory.FACTORY_BEAN_PREFIX));
}

getObjectFromFactoryBean

protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
		if (factory.isSingleton() && containsSingleton(beanName)) {
			synchronized (getSingletonMutex()) {
				// 从缓存中获取
				Object object = this.factoryBeanObjectCache.get(beanName);
				if (object == null) {
					object = doGetObjectFromFactoryBean(factory, beanName);
					// Only post-process and store if not put there already during getObject() call above
					// (e.g. because of circular reference processing triggered by custom getBean calls)
					Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
					if (alreadyThere != null) {
						object = alreadyThere;
					}
					else {
						if (shouldPostProcess) {
							if (isSingletonCurrentlyInCreation(beanName)) {
								// Temporarily return non-post-processed object, not storing it yet..
								return object;
							}
							//将BeanName放入正在创建的Bean的Set集合
							beforeSingletonCreation(beanName);
							try {
								// 对FactoryBean创建的对象进行后置处理
								object = postProcessObjectFromFactoryBean(object, beanName);
							}
							catch (Throwable ex) {
								throw new BeanCreationException(beanName,
										"Post-processing of FactoryBean's singleton object failed", ex);
							}
							finally {
								afterSingletonCreation(beanName);
							}
						}
						if (containsSingleton(beanName)) {
							this.factoryBeanObjectCache.put(beanName, object);
						}
					}
				}
				return object;
			}
		}
		else {
			Object object = doGetObjectFromFactoryBean(factory, beanName);
			if (shouldPostProcess) {
				try {
					object = postProcessObjectFromFactoryBean(object, beanName);
				}
				catch (Throwable ex) {
					throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
				}
			}
			return object;
		}
	}

protected void beforeSingletonCreation(String beanName) {
		if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
			throw new BeanCurrentlyInCreationException(beanName);
		}
	}

/**
	 * Callback after singleton creation.
	 * <p>The default implementation marks the singleton as not in creation anymore.
	 * @param beanName the name of the singleton that has been created
	 * @see #isSingletonCurrentlyInCreation
	 */
	protected void afterSingletonCreation(String beanName) {
		if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.remove(beanName)) {
			throw new IllegalStateException("Singleton '" + beanName + "' isn't currently in creation");
		}
	}

FactoryBean

public interface FactoryBean<T> {


	String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";


	@Nullable
	T getObject() throws Exception;

	
	@Nullable
	Class<?> getObjectType();

	default boolean isSingleton() {
		return true;
	}

}

public class Student {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

@Component("studentFactoryBean")
public class StudentFactoryBean implements FactoryBean<Student> {

    @Override
    public Student getObject() throws Exception {
        System.out.println("StudentFactoryBean create student");
        Student student = new Student();
        student.setName("jack");
        student.setAge(18);
        return student;
    }


    @Override
    public Class<?> getObjectType() {
        return Student.class;
    }
}

public static void main(String[] args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext("cn.dotfashion.soa.demo.**");
        Student student = (Student) ctx.getBean("studentFactoryBean");
        FactoryBean student1 = (FactoryBean) ctx.getBean("&studentFactoryBean");
        System.out.println(student);
        System.out.println(student1);

    }

StudentFactoryBean create student
cn.dotfashion.soa.demo.factoyBean.Student@5f683daf[name=jack,age=18]
cn.dotfashion.soa.demo.factoyBean.StudentFactoryBean@7e9131d5