目录
前言
spring，对不起，我不知道你这么强.jpg（跪地）
什么是BeanDefinition
BeanDefinition用于保存Bean的相关信息，是生产Bean的原材料，BeanDefinition是一个顶端接口，在此基础上，衍生出了保存特定Bean的BeanDefinition
BeanDefinition的继承体系
GenericBeanDefinition：除了指定类、可选的构造函数参数值和属性参数外，还可以通过parenetName属性灵活设置父类的类全限定名
RootBeanDefinition：在注册Bean阶段最常使用的就是RootBeanDefinition，它对应<bean>元素标签，在配置文件中可以定义父<bean>和子<bean>，父bean可以用RootBeanDefinition，子Bean可以用ChildBeanDefinition，从spring2.5开始，对于子bean，更常使用GenericBeanDefinition
AnnotatedGenericBeanDefinition：以@Configuration注解标记的类会解析为AnnotatedGenericBeanDefintion
ConfigurationClassBeanDefinition：以@Bean注解标记的方法对应的Bean会解析为ConfigurationClassBeanDefinition
ScannedGenericBeanDefinition：以@Component、@Service、@Controller注解标记的类会解析为ScannedGenericBeanDefinition
BeanDefinition源码
BeanDefinition继承了两个接口
- AttributeAccessor：这个接口定义了对对象的元数据（我的理解是未加工的数据，例如直接从xml文件中解析得到的数据）进行操作的基本方法（设置值、获取值），定义的方法如下：
//将name定义的属性设置为提供的value值。如果value的值为null，则该属性为{@link #removeAttribute removed}。 //通常，用户应该注意通过使用完全限定的名称（可能使用类或包名称作为前缀）来防止与其他元数据属性重叠。 void setAttribute(String name, Object value); //获取标识为name的属性的值。 Object getAttribute(String name); //删除标识为name的属性，并返回属性值 Object removeAttribute(String name); //如果名为name的属性是否存在，存在返回true，否则返回false。 boolean hasAttribute(String name); //返回所有属性的名称。 String[] attributeNames(); - BeanMetadataElement：返回配置源对象，可以返回null：
/** * Return the configuration source {@code Object} for this metadata element * (may be {@code null}). */ @Nullable Object getSource();
源码（不翻译了）：
public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {
/**
* Scope identifier for the standard singleton scope: "singleton".
* <p>Note that extended bean factories might support further scopes.
* @see #setScope
*/
//单例的标识符
String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;
/**
* Scope identifier for the standard prototype scope: "prototype".
* <p>Note that extended bean factories might support further scopes.
* @see #setScope
*/
//原型的标识符
String SCOPE_PROTOTYPE = ConfigurableBeanFactory.SCOPE_PROTOTYPE;
/**
* Role hint indicating that a {@code BeanDefinition} is a major part
* of the application. Typically corresponds to a user-defined bean.
*/
//Bean的角色，用户定义的Bean
int ROLE_APPLICATION = 0;
/**
* Role hint indicating that a {@code BeanDefinition} is a supporting
* part of some larger configuration, typically an outer
* {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
* {@code SUPPORT} beans are considered important enough to be aware
* of when looking more closely at a particular
* {@link org.springframework.beans.factory.parsing.ComponentDefinition},
* but not when looking at the overall configuration of an application.
*/
//Bean的角色，Bean来自配置文件
int ROLE_SUPPORT = 1;
/**
* Role hint indicating that a {@code BeanDefinition} is providing an
* entirely background role and has no relevance to the end-user. This hint is
* used when registering beans that are completely part of the internal workings
* of a {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
*/
//Bean的角色，Bean来自spring
int ROLE_INFRASTRUCTURE = 2;
/**
* Set the name of the parent definition of this bean definition, if any.
*/
void setParentName(@Nullable String parentName);
/**
* Return the name of the parent definition of this bean definition, if any.
*/
@Nullable
String getParentName();
/**
* Specify the bean class name of this bean definition.
* <p>The class name can be modified during bean factory post-processing,
* typically replacing the original class name with a parsed variant of it.
* @see #setParentName
* @see #setFactoryBeanName
* @see #setFactoryMethodName
*/
void setBeanClassName(@Nullable String beanClassName);
/**
* Return the current bean class name of this bean definition.
* <p>Note that this does not have to be the actual class name used at runtime, in
* case of a child definition overriding/inheriting the class name from its parent.
* Also, this may just be the class that a factory method is called on, or it may
* even be empty in case of a factory bean reference that a method is called on.
* Hence, do <i>not</i> consider this to be the definitive bean type at runtime but
* rather only use it for parsing purposes at the individual bean definition level.
* @see #getParentName()
* @see #getFactoryBeanName()
* @see #getFactoryMethodName()
*/
@Nullable
String getBeanClassName();
/**
* Override the target scope of this bean, specifying a new scope name.
* @see #SCOPE_SINGLETON
* @see #SCOPE_PROTOTYPE
*/
void setScope(@Nullable String scope);
/**
* Return the name of the current target scope for this bean,
* or {@code null} if not known yet.
*/
@Nullable
String getScope();
/**
* Set whether this bean should be lazily initialized.
* <p>If {@code false}, the bean will get instantiated on startup by bean
* factories that perform eager initialization of singletons.
*/
void setLazyInit(boolean lazyInit);
/**
* Return whether this bean should be lazily initialized, i.e. not
* eagerly instantiated on startup. Only applicable to a singleton bean.
*/
boolean isLazyInit();
/**
* Set the names of the beans that this bean depends on being initialized.
* The bean factory will guarantee that these beans get initialized first.
*/
void setDependsOn(@Nullable String... dependsOn);
/**
* Return the bean names that this bean depends on.
*/
@Nullable
String[] getDependsOn();
/**
* Set whether this bean is a candidate for getting autowired into some other bean.
* <p>Note that this flag is designed to only affect type-based autowiring.
* It does not affect explicit references by name, which will get resolved even
* if the specified bean is not marked as an autowire candidate. As a consequence,
* autowiring by name will nevertheless inject a bean if the name matches.
*/
void setAutowireCandidate(boolean autowireCandidate);
/**
* Return whether this bean is a candidate for getting autowired into some other bean.
*/
boolean isAutowireCandidate();
/**
* Set whether this bean is a primary autowire candidate.
* <p>If this value is {@code true} for exactly one bean among multiple
* matching candidates, it will serve as a tie-breaker.
*/
void setPrimary(boolean primary);
/**
* Return whether this bean is a primary autowire candidate.
*/
boolean isPrimary();
/**
* Specify the factory bean to use, if any.
* This the name of the bean to call the specified factory method on.
* @see #setFactoryMethodName
*/
void setFactoryBeanName(@Nullable String factoryBeanName);
/**
* Return the factory bean name, if any.
*/
@Nullable
String getFactoryBeanName();
/**
* Specify a factory method, if any. This method will be invoked with
* constructor arguments, or with no arguments if none are specified.
* The method will be invoked on the specified factory bean, if any,
* or otherwise as a static method on the local bean class.
* @see #setFactoryBeanName
* @see #setBeanClassName
*/
void setFactoryMethodName(@Nullable String factoryMethodName);
/**
* Return a factory method, if any.
*/
@Nullable
String getFactoryMethodName();
/**
* Return the constructor argument values for this bean.
* <p>The returned instance can be modified during bean factory post-processing.
* @return the ConstructorArgumentValues object (never {@code null})
*/
ConstructorArgumentValues getConstructorArgumentValues();
/**
* Return if there are constructor argument values defined for this bean.
* @since 5.0.2
*/
default boolean hasConstructorArgumentValues() {
return !getConstructorArgumentValues().isEmpty();
}
/**
* Return the property values to be applied to a new instance of the bean.
* <p>The returned instance can be modified during bean factory post-processing.
* @return the MutablePropertyValues object (never {@code null})
*/
//来自.properties文件中的键值对
MutablePropertyValues getPropertyValues();
/**
* Return if there are property values values defined for this bean.
* @since 5.0.2
*/
default boolean hasPropertyValues() {
return !getPropertyValues().isEmpty();
}
/**
* Set the name of the initializer method.
* @since 5.1
*/
void setInitMethodName(@Nullable String initMethodName);
/**
* Return the name of the initializer method.
* @since 5.1
*/
@Nullable
String getInitMethodName();
/**
* Set the name of the destroy method.
* @since 5.1
*/
void setDestroyMethodName(@Nullable String destroyMethodName);
/**
* Return the name of the destroy method.
* @since 5.1
*/
@Nullable
String getDestroyMethodName();
/**
* Set the role hint for this {@code BeanDefinition}. The role hint
* provides the frameworks as well as tools with an indication of
* the role and importance of a particular {@code BeanDefinition}.
* @since 5.1
* @see #ROLE_APPLICATION
* @see #ROLE_SUPPORT
* @see #ROLE_INFRASTRUCTURE
*/
void setRole(int role);
/**
* Get the role hint for this {@code BeanDefinition}. The role hint
* provides the frameworks as well as tools with an indication of
* the role and importance of a particular {@code BeanDefinition}.
* @see #ROLE_APPLICATION
* @see #ROLE_SUPPORT
* @see #ROLE_INFRASTRUCTURE
*/
int getRole();
/**
* Set a human-readable description of this bean definition.
* @since 5.1
*/
void setDescription(@Nullable String description);
/**
* Return a human-readable description of this bean definition.
*/
@Nullable
String getDescription();
// Read-only attributes
/**
* Return whether this a <b>Singleton</b>, with a single, shared instance
* returned on all calls.
* @see #SCOPE_SINGLETON
*/
boolean isSingleton();
/**
* Return whether this a <b>Prototype</b>, with an independent instance
* returned for each call.
* @since 3.0
* @see #SCOPE_PROTOTYPE
*/
boolean isPrototype();
/**
* Return whether this bean is "abstract", that is, not meant to be instantiated.
*/
boolean isAbstract();
/**
* Return a description of the resource that this bean definition
* came from (for the purpose of showing context in case of errors).
*/
@Nullable
String getResourceDescription();
/**
* Return the originating BeanDefinition, or {@code null} if none.
* Allows for retrieving the decorated bean definition, if any.
* <p>Note that this method returns the immediate originator. Iterate through the
* originator chain to find the original BeanDefinition as defined by the user.
*/
@Nullable
BeanDefinition getOriginatingBeanDefinition();
}总结一下，BeanDefinition定义了如下信息：
1、对对象元数据进行操作的方法（设置与获取属性）
2、描述对象画像的操作（一系列的get、set、is方法）
3、定义Bean的角色常量
BeanDefinition只是定义了一系列的操作，描述Bean画像的相关属性交给了子类AbstractBeanDefinition，这个子类实现了BeanDefinition定义的一系列操作
如有错误，欢迎指出