BeanDefinitionRegistry
在阐释BeanDefinitionRegistry之前，我们有必要简单提一下BeanDefinition。BeanDefinition是spring容器中bean的定义，这些定义可以是xml配置，可以是注解配置，还可以是别的。
BeanDefinitionRegistry是一个接口，中文名为BeanDefinition注册器，继承了AliasRegistry接口，同时增加了对BeanDefinition的管理。
因此，我们可以说，这个接口包含以下几方面的功能：
-
BeanDefinition管理的功能 - 包含对别名管理的功能
public interface BeanDefinitionRegistry extends AliasRegistry {
/**
* 注册BeanDefinition
* Register a new bean definition with this registry.
* Must support RootBeanDefinition and ChildBeanDefinition.
* @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;
/**
* 移除BeanDefinition
* Remove the BeanDefinition for the given name.
* @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;
/**
* 根据bean名称获取BeanDefinition
* Return the BeanDefinition for the given bean name.
* @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;
/**
* 判断是否包含bean名称
* Check if this registry contains a bean definition with the given name.
* @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);
/**
* 获取BeanDefinition的所有名称数组
* 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();
/**
* 获取BeanDefinition的数量
* Return the number of beans defined in the registry.
* @return the number of beans defined in the registry
*/
int getBeanDefinitionCount();
/**
* 判断beanName对应的BeanDefinition是否被使用了
* 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中的实现
DefaultListableBeanFactory是BeanFactory的具体实现，内容繁多且负责，这儿仅仅分析实现BeanDefinitionRegistry接口的那些方法。
涉及到的字段信息
// BeanDefinition容器
/** Map of bean definition objects, keyed by bean name. */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
// BeanDefinition名称列表
/** List of bean definition names, in registration order. */
private volatile List<String> beanDefinitionNames = new ArrayList<>(256);
// 手动单例名称列表
/** List of names of manually registered singletons, in registration order. */
private volatile Set<String> manualSingletonNames = new LinkedHashSet<>(16);
// 冻结名称列表
/** Cached array of bean definition names in case of frozen configuration. */
@Nullable
private volatile String[] frozenBeanDefinitionNames;
// 冻结开关，默认关闭
/** Whether bean definition metadata may be cached for all beans. */
private volatile boolean configurationFrozen = false;
registerBeanDefinition
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
// beanName不允许为空，beanDefinition不允许为null
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
// 如果是AbstractBeanDefinition类型，则需要调用`validate()`校验一下正确性
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
// 尝试从BeanDefinition容器中查找
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
// BeanDefinition容器中存在，则做了以下事情：
// 1. 如果不允许重复注册，则抛出异常
// 2. 条件满足的情况下，记录一帕拉日志
// 3. 注册到BeanDefinition容器
if (existingDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
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);
}
// BeanDefinition容器中不存在
// 1. 如果bean创建已经开始，则需要在锁环境下完成注册操作
// 2. 如果bean创建还未开始，则不需要在所环境下操作，因为这个时候所有的操作都是在一个线程内完成
// 3. 清空冻结名称列表，目的是为了后续查找方便
else {
if (hasBeanCreationStarted()) {
// 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 {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
// 如果BeanDefinition容器中存在，或者当前BeanDefinition是一个单例定义，则需要重置BeanDefinition
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
resetBeanDefinition
/**
* 重置BeanDefinition，包括beanName被移除或替换的场景。
* Reset all bean definition caches for the given bean,
* including the caches of beans that are derived from it.
* <p>Called after an existing bean definition has been replaced or removed,
* triggering {@link #clearMergedBeanDefinition}, {@link #destroySingleton}
* and {@link MergedBeanDefinitionPostProcessor#resetBeanDefinition} on the
* given bean and on all bean definitions that have the given bean as parent.
* @param beanName the name of the bean to reset
* @see #registerBeanDefinition
* @see #removeBeanDefinition
*/
protected void resetBeanDefinition(String beanName) {
// Remove the merged bean definition for the given bean, if already created.
// 清除合并的BeanDefinition
clearMergedBeanDefinition(beanName);
// Remove corresponding bean from singleton cache, if any. Shouldn't usually
// be necessary, rather just meant for overriding a context's default beans
// (e.g. the default StaticMessageSource in a StaticApplicationContext).
// 销毁单例
destroySingleton(beanName);
// Notify all post-processors that the specified bean definition has been reset.
// 调用MergedBeanDefinitionPostProcessor进行回调处理
for (BeanPostProcessor processor : getBeanPostProcessors()) {
if (processor instanceof MergedBeanDefinitionPostProcessor) {
((MergedBeanDefinitionPostProcessor) processor).resetBeanDefinition(beanName);
}
}
// Reset all bean definitions that have the given bean as parent (recursively).
for (String bdName : this.beanDefinitionNames) {
if (!beanName.equals(bdName)) {
BeanDefinition bd = this.beanDefinitionMap.get(bdName);
// Ensure bd is non-null due to potential concurrent modification
// of the beanDefinitionMap.
// 父名称和当前名称相同的情况下，需要递归调用此方法
if (bd != null && beanName.equals(bd.getParentName())) {
resetBeanDefinition(bdName);
}
}
}
}
removeBeanDefinition
public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
Assert.hasText(beanName, "'beanName' must not be empty");
// 移除不存在的BeanDefinition，会抛出异常
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);
}
// 和注册逻辑一样，Bean创建开始了，则需要在锁环境下进行移除操作，同时额外执行以下操作：
// 1. 清空冻结名称列表
// 2. 重置BeanDefinition
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 {
// Still in startup registration phase
this.beanDefinitionNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
resetBeanDefinition(beanName);
}
getBeanDefinition && containsBeanDefinition && getBeanDefinitionCount
很简单！
public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
BeanDefinition bd = this.beanDefinitionMap.get(beanName);
if (bd == null) {
if (logger.isTraceEnabled()) {
logger.trace("No bean named '" + beanName + "' found in " + this);
}
throw new NoSuchBeanDefinitionException(beanName);
}
return bd;
}
public boolean containsBeanDefinition(String beanName) {
Assert.notNull(beanName, "Bean name must not be null");
return this.beanDefinitionMap.containsKey(beanName);
}
public int getBeanDefinitionCount() {
return this.beanDefinitionMap.size();
}
getBeanDefinitionNames
首先从frozenBeanDefinitionNames获取，如果为null，再从beanDefinitionNames获取。
【注意】：为了线程安全，这儿使用了数组的clone()操作。
public String[] getBeanDefinitionNames() {
String[] frozenNames = this.frozenBeanDefinitionNames;
if (frozenNames != null) {
return frozenNames.clone();
}
else {
return StringUtils.toStringArray(this.beanDefinitionNames);
}
}
isBeanNameInUse
这个方法在AbstractBeanFactory类里面。beanName是否在使用，有3种情况：
- 是一个别名
- 是一个本地Bean的名称
- 通过这个名字创建了一个内部bean（也叫依赖bean）
public boolean isBeanNameInUse(String beanName) {
return isAlias(beanName) || containsLocalBean(beanName) || hasDependentBean(beanName);
}
总结
至此，我们粗略地对BeanDefinitionRegistry及其实现DefaultListableBeanFactory进行了分析。相对来说，比较简单，主要是对ConcurrentHashMap这种集合对象进行增删改查操作。
