Spring BeanDefinitionRegistry 接口

Spring BeanDefinitionRegistry 接口

Registry 登记/注册 顾名思义, 该接口设计的目的是用于保存和管理 Bean定义描述(BeanDefinition)

org.springframework.beans.factory.support.BeanDefinitionRegistry

package org.springframework.beans.factory.support;

import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.core.AliasRegistry;

/**
 * Interface for registries that hold bean definitions, for example RootBeanDefinition
 * and ChildBeanDefinition instances. Typically implemented by BeanFactories that
 * internally work with the AbstractBeanDefinition hierarchy.
 *
 * Registry 登记/注册 顾名思义 该接口设计的目的是用于保存和管理 Bean定义描述(BeanDefinition), 例如:  RootBeanDefinition 和 ChildBeanDefinition 实例
 *
 * <p>This is the only interface in Spring's bean factory packages that encapsulates
 * <i>registration</i> of bean definitions. The standard BeanFactory interfaces
 * only cover access to a <i>fully configured factory instance</i>.
 *
 * <p>Spring's bean definition readers expect to work on an implementation of this
 * interface. Known implementors within the Spring core are DefaultListableBeanFactory
 * and GenericApplicationContext.
 *
 * @author Juergen Hoeller
 * @since 26.11.2003
 * @see org.springframework.beans.factory.config.BeanDefinition
 * @see AbstractBeanDefinition
 * @see RootBeanDefinition
 * @see ChildBeanDefinition
 * @see DefaultListableBeanFactory
 * @see org.springframework.context.support.GenericApplicationContext
 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 * @see PropertiesBeanDefinitionReader
 */
public interface BeanDefinitionRegistry extends AliasRegistry {

	/**
	 * Register a new bean definition with this registry.
	 * Must support RootBeanDefinition and ChildBeanDefinition.
	 *
	 * 根据名称注册一个新的 BeanDefinition
	 * @param beanName the name of the bean instance to register
	 * @param beanDefinition definition of the bean instance to register
	 * @throws BeanDefinitionStoreException if the BeanDefinition is invalid
	 * @throws BeanDefinitionOverrideException if there is already a BeanDefinition
	 * for the specified bean name and we are not allowed to override it
	 * @see GenericBeanDefinition
	 * @see RootBeanDefinition
	 * @see ChildBeanDefinition
	 */
	void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException;

	/**
	 * Remove the BeanDefinition for the given name.
	 *
	 * 根据名称移除一个 BeanDefinition
	 * @param beanName the name of the bean instance to register
	 * @throws NoSuchBeanDefinitionException if there is no such bean definition
	 */
	void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;

	/**
	 * Return the BeanDefinition for the given bean name.
	 *
	 * 根据名称获取 BeanDefinition
	 * @param beanName name of the bean to find a definition for
	 * @return the BeanDefinition for the given name (never {@code null})
	 * @throws NoSuchBeanDefinitionException if there is no such bean definition
	 */
	BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;

	/**
	 * Check if this registry contains a bean definition with the given name.
	 * 检查给定名称是否已存在
	 * @param beanName the name of the bean to look for
	 * @return if this registry contains a bean definition with the given name
	 */
	boolean containsBeanDefinition(String beanName);

	/**
	 * Return the names of all beans defined in this registry.
	 * @return the names of all beans defined in this registry,
	 * or an empty array if none defined
	 */
	String[] getBeanDefinitionNames();

	/**
	 * Return the number of beans defined in the registry.
	 * @return the number of beans defined in the registry
	 */
	int getBeanDefinitionCount();

	/**
	 * Determine whether the bean definition for the given name is overridable,
	 * i.e. whether {@link #registerBeanDefinition} would successfully return
	 * against an existing definition of the same name.
	 * <p>The default implementation returns {@code true}.
	 *
	 *  判定给定的名称是否允许覆盖它的 BeanDefinition
	 *
	 * @param beanName the name to check
	 * @return whether the definition for the given bean name is overridable
	 * @since 6.1
	 */
	default boolean isBeanDefinitionOverridable(String beanName) {
		return true;
	}

	/**
	 * Determine whether the given bean name is already in use within this registry,
	 * i.e. whether there is a local bean or alias registered under this name.
	 * @param beanName the name to check
	 * @return whether the given bean name is already in use
	 */
	boolean isBeanNameInUse(String beanName);
}

DefaultListableBeanFactory 的实现

大多数情况下, 我们项目的 BeanFactory 的实例是 DefaultListableBeanFactory, 它也是一个 BeanDefinitionRegistry

org.springframework.beans.factory.support.DefaultListableBeanFactory#registerBeanDefinition

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory  
       implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
       
       
       .........
	
	/**
	 * 注册一个 BeanDefinition 的方法
	 */
	@Override
	public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {

		Assert.hasText(beanName, "Bean name must not be empty");
		Assert.notNull(beanDefinition, "BeanDefinition must not be null");

		if (beanDefinition instanceof AbstractBeanDefinition abd) {
			try {
				abd.validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}
		// 获取一下是否有这个 bean 的 BeanDefinition
		BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
		if (existingDefinition != null) {
			// 如果有 且 不允许覆盖, 则抛出 BeanDefinitionOverrideException
			if (!isBeanDefinitionOverridable(beanName)) {
				throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
			}
			else if (existingDefinition.getRole() < beanDefinition.getRole()) {
				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
				if (logger.isInfoEnabled()) {
					logger.info("Overriding user-defined bean definition for bean '" + beanName +
							"' with a framework-generated bean definition: replacing [" +
							existingDefinition + "] with [" + beanDefinition + "]");
				}
			}
			else if (!beanDefinition.equals(existingDefinition)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Overriding bean definition for bean '" + beanName +
							"' with a different definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			else {
				if (logger.isTraceEnabled()) {
					logger.trace("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
			if (isAlias(beanName)) {
				//判断下, 别名是否覆盖.
				String aliasedName = canonicalName(beanName);
				if (!isBeanDefinitionOverridable(aliasedName)) {
					if (containsBeanDefinition(aliasedName)) {  // alias for existing bean definition
						throw new BeanDefinitionOverrideException(
								beanName, beanDefinition, getBeanDefinition(aliasedName));
					}
					else {  // alias pointing to non-existing bean definition
						throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
								"Cannot register bean definition for bean '" + beanName +
								"' since there is already an alias for bean '" + aliasedName + "' bound.");
					}
				}
				else {
					removeAlias(beanName);
				}
			}
			if (hasBeanCreationStarted()) {
				//bean 是否已经开始创建中. 后面再研究, 不是这个分支
				// Cannot modify startup-time collection elements anymore (for stable iteration)
				synchronized (this.beanDefinitionMap) {
					this.beanDefinitionMap.put(beanName, beanDefinition);
					List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
					updatedDefinitions.addAll(this.beanDefinitionNames);
					updatedDefinitions.add(beanName);
					this.beanDefinitionNames = updatedDefinitions;
					removeManualSingletonName(beanName);
				}
			}
			else {
				// 放到 beanDefinitionMap, key 是 beanName; value 是 beanDefinition;
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				// 别名 添加到 beanDefinitionNames
				this.beanDefinitionNames.add(beanName);
				removeManualSingletonName(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

		if (existingDefinition != null || containsSingleton(beanName)) {
			resetBeanDefinition(beanName);
		}
		else if (isConfigurationFrozen()) {
			clearByTypeCache();
		}
	}
	/**
	 * 移除一个 BeanDefinition 的方法
	 */
	@Override
	public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
		Assert.hasText(beanName, "'beanName' must not be empty");

		//从 beanDefinitionMap 中移除
		BeanDefinition bd = this.beanDefinitionMap.remove(beanName);
		if (bd == null) {
			if (logger.isTraceEnabled()) {
				logger.trace("No bean named '" + beanName + "' found in " + this);
			}
			throw new NoSuchBeanDefinitionException(beanName);
		}
		//bean 是否已经开始创建中
		if (hasBeanCreationStarted()) {
			// Cannot modify startup-time collection elements anymore (for stable iteration)
			synchronized (this.beanDefinitionMap) {
				List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames);
				updatedDefinitions.remove(beanName);
				this.beanDefinitionNames = updatedDefinitions;
			}
		}
		else {
			//从 beanDefinitionNames 中移除
			// Still in startup registration phase
			this.beanDefinitionNames.remove(beanName);
		}
		this.frozenBeanDefinitionNames = null;

		resetBeanDefinition(beanName);
	}
    ........ 

对于 DefaultListableBeanFactory 的实现主要就是使用两个集合存起来:

	/**
	 * 这个 Map 存储所有已注册 BeanDefinition, 其中 key是bean主要name, value 是 BeanDefinition
	 */
	private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);

	/**  
	 * 这个list 存储所有的 bean definition 名称  
	 */  
	private volatile List<String> beanDefinitionNames = new ArrayList<>(256);