BeanDefinition接口

BeanDefinition 描述一个 Bean 实例，这个实例有哪些属性值、构造函数以及一些其他信息，就是描述Bean实例的信息。

BeanDefinition是一个接口，允许BeanFactoryPostProcessor 内省和修改属性值和其他 Bean 元数据。
点击了解BeanFactoryPostProcessor

意义

在spring流程中是现有BeanDefinition再有bean，bean是根据BeanDefinition中的信息去创建的，当然在还没创建bean的时候还可以修改BeanDefinition中的信息，这个就是BeanFactoryPostProcessor 接口的主要功能，如我们在xml中定义的${jdbc.name}最终替换为真正的值就是在实现BeanFactoryPostProcessor 接口完成的。

源码

package org.springframework.beans.factory.config;

import org.springframework.beans.BeanMetadataElement;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.core.AttributeAccessor;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;

/**
 * A BeanDefinition describes a bean instance, which has property values,
 * constructor argument values, and further information supplied by
 * concrete implementations.
 *
 * <p>This is just a minimal interface: The main intention is to allow a
 * {@link BeanFactoryPostProcessor} to introspect and modify property values
 * and other bean metadata.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 19.03.2004
 * @see ConfigurableListableBeanFactory#getBeanDefinition
 * @see org.springframework.beans.factory.support.RootBeanDefinition
 * @see org.springframework.beans.factory.support.ChildBeanDefinition
 */
public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {

	/**
	 * Scope identifier for the standard singleton scope: {@value}.
	 * <p>Note that extended bean factories might support further scopes.
	 * @see #setScope
	 * @see ConfigurableBeanFactory#SCOPE_SINGLETON
	 */
	String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;

	/**
	 * Scope identifier for the standard prototype scope: {@value}.
	 * <p>Note that extended bean factories might support further scopes.
	 * @see #setScope
	 * @see ConfigurableBeanFactory#SCOPE_PROTOTYPE
	 */
	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.
	 */
	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.
	 */
	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}.
	 */
	int ROLE_INFRASTRUCTURE = 2;


	// Modifiable attributes

	/**
	 * 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.
	 * <p>Note that dependencies are normally expressed through bean properties or
	 * constructor arguments. This property should just be necessary for other kinds
	 * of dependencies like statics (*ugh*) or database preparation on startup.
	 */
	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.
	 * @see #setFallback
	 */
	void setPrimary(boolean primary);

	/**
	 * Return whether this bean is a primary autowire candidate.
	 */
	boolean isPrimary();

	/**
	 * Set whether this bean is a fallback autowire candidate.
	 * <p>If this value is {@code true} for all beans but one among multiple
	 * matching candidates, the remaining bean will be selected.
	 * @since 6.2
	 * @see #setPrimary
	 */
	void setFallback(boolean fallback);

	/**
	 * Return whether this bean is a fallback autowire candidate.
	 * @since 6.2
	 */
	boolean isFallback();

	/**
	 * Specify the factory bean to use, if any.
	 * This is the name of the bean to call the specified factory method on.
	 * <p>A factory bean name is only necessary for instance-based factory methods.
	 * For static factory methods, the method will be derived from the bean class.
	 * @see #setFactoryMethodName
	 * @see #setBeanClassName
	 */
	void setFactoryBeanName(@Nullable String factoryBeanName);

	/**
	 * Return the factory bean name, if any.
	 * <p>This will be {@code null} for static factory methods which will
	 * be derived from the bean class instead.
	 * @see #getFactoryMethodName()
	 * @see #getBeanClassName()
	 */
	@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.
	 * @see #getFactoryBeanName()
	 * @see #getBeanClassName()
	 */
	@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
	 * @see #getConstructorArgumentValues()
	 */
	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})
	 */
	MutablePropertyValues getPropertyValues();

	/**
	 * Return if there are property values defined for this bean.
	 * @since 5.0.2
	 * @see #getPropertyValues()
	 */
	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 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 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 a resolvable type for this bean definition,
	 * based on the bean class or other specific metadata.
	 * <p>This is typically fully resolved on a runtime-merged bean definition
	 * but not necessarily on a configuration-time definition instance.
	 * @return the resolvable type (potentially {@link ResolvableType#NONE})
	 * @since 5.2
	 * @see ConfigurableBeanFactory#getMergedBeanDefinition
	 */
	ResolvableType getResolvableType();

	/**
	 * 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
	 * itself but rather just serving as parent for concrete child bean definitions.
	 */
	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.
	 * <p>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();

}