classBeanDefinitionThe inheritance system of

Through the in-depth analysis of the BeanFactory in the previous chapter, we found that the BeanFactory abstracts the instantiation process of the Bean object into the BeanDefinition class. Similarly, by analyzing the class inheritance structure of BeanDefinition (see figure below).

Interface inheritance

From the figure, we can see that BeanDefination mainly inherits from AttributeAccessor and BeanMetadataElement. The former encapsulates operations related to object attributes (such as add, delete, modify). The latter is the original definition source that describes BeanDefination (the configuration source {@code Object} for this metadata element), For example, if it is a Spring Bean based Annotation configuration, The source might correspond to StandardMethodMetadata (defined by the @Bean annotation) or File (defined by the @Component annotation).

Class implements

From the diagram, we found that AttributeAccessorSupport provide general properties of encapsulation, operation BeanMetadataAttributeAccessor interface providing Source related, speaking, reading and writing; Based on AttributeAccessorSupport, the attribute format is unified into the class BeanMetadataAttribute. Finally, by inheriting class BeanMetadataAttribute to implement interface BeanDefinition, we get abstract class AbstractBeanDefinition, the basic BeanDefination.

AbstractBeanDefinition has three implementation classes, depending on the usage scenario: RootBeanDefinition (used to instantiate bean objects, Other types of BeanDefinitions need to be converted to RootBeanDefinitions to be instantiated by BeanFactory), childBeanDefinitions (beanDefinitions are supported through the parent property Data inheritance), GenericBeanDefinition (generic BeanDefination). By @ Bean, @ Component annotation registered BeanDefination, are generally not AnnotatedGenericBeanDefinition or ScannedGenericBeanDefinition, The difference between the two is that the former is based on the Class object instance to get related attributes, while the latter is based on ASM bytecode parsing, without Class loading.

interfaceBeanDefinitionRelated field definitions

Field name (bold fields support both write and read properties, other fields support read fields) meaning
parentName The parent of BeanDefination, used for inheritance of related attributes, can be null
beanClassName The Class name of the bean, which can be null
scope Scope of bean. IoC container provides singleton and Prototype scope to support business expansion. Default is Singleton
lazyInit Lazy loading or not: The default is false, meaning that the Bean is initialized in the IoC container, not when the application acquires the Bean
dependsOn Describes the Spring beans that the current bean depends on before initialization, in which order the BeanFactory ensures
autowireCandidate Is a set of candidates to inject the current bean as a type of another bean when the user does not specify a specific reference. The default is true
primary Combine with the previous fieldautowireCandidate, whether the bean is the preferred object when it appears in the candidate set. The default is false
factoryBeanName The Bean Name of the factory class used to instantiate the Bean, which can be null
factoryMethodName The method name of the factory class used to instantiate the Bean, which can be null
constructorArgumentValues Functions that describe Bean initialization
propertyValues Describes the value of the bean-related properties
initMethodName Describes a custom initialization method inside a Bean
destroyMethodName Describes a custom destruction method inside a Bean
role The role of Bean, generally divided intoAPPLICATION,SUPPORT,INFRASTRUCTURE
description Bean description
ResolvableType The Abstract representation of the Type object in Spring provides user-friendly extraction of generic types
Abstract Whether the type is Abstract
ResourceDescription The description of the BeanDefination definition source is used to display scenarios such as logs

classAbstractBeanDefinitionExtended field of

AbstractBeanDefinition provides the following fields in addition to the interface BeanDefinition

  • AutowireMode: Describes the pattern for auto-assembly beans, divided intoAUTOWIRE_BY_NAME(Indicating auto-assembly Bean properties by name, applies to all Bean property Settings and constructor parameter Settings),AUTOWIRE_BY_TYPEAutomatic assembly of Bean property constants by type (applies to all Bean property Settings and constructor parameter Settings),AUTOWIRE_CONSTRUCTOR(Automatic assembly, suitable for constructor parameter Settings),AUTOWIRE_NO(Do not set related types).
  • DependencyCheck: Checks the property dependency of the BeanDEPENDENCY_CHECK_NONE(No dependency check is performed),DEPENDENCY_CHECK_OBJECTS(only object references are checked),DEPENDENCY_CHECK_SIMPLE(Check simple types only),DEPENDENCY_CHECK_ALL(Detect all dependencies), etc
  • Qualifiers: type isMap<String, AutowireCandidateQualifier>, describing qualifier objects for type-dependent autowiring candidates.
  • MethodOverrides: method rewrite set, which describes the rewrite information performed by the Bean method, implementatively divided intoLookupOverride 和 ReplaceOverride, corresponding to LookupMethod and ReplaceMethod. For details, seeMethod Injection.
  • EnforceInitMethod: Whether the custom initialization method is enforceable. The default is false, logical referenceorg.springframework.beans.factory.support.AbstractBeanDefinition#applyDefaults
  • EnforceDestroyMethod: Whether the custom destruction method is enforceable. The default is false, logical referenceorg.springframework.beans.factory.support.AbstractBeanDefinition#applyDefaults
  • Synthetic: Whether the current class is a synthetic class

BeanDefination inspection

BeanDefination in these fields has certain constraints, specific logic in the org. Springframework. Beans. Factory. Support. AbstractBeanDefinition# validate, MethodOverrides and FactoryMethodName are not allowed to appear repeatedly due to conflicting initialization strategies.