一、依赖查找的依赖来源
1、自定义的BeanDefinition
1、使用xml方式配置的
<bean id="user" class="com...User">
2、使用@Bean
@Bean public User user(){
...}
3、使用BeanDefinitionBuilder自己构建的
总之，一切用户自己定义的bean。（下面详细介绍）
2、外部化配置的单体对象
就是已初始化的外部 Java 对象，在 Spring 容器中是唯一的。（下面详细介绍）
3、Spring 內建 BeanDefintion
使用AnnotationConfigUtils定义的BeanDefintion
| Bean 名称 | Bean 实例 | 使用场景 |
|---|---|---|
| org.springframework.context.annotation.internalConfigurationAnnotationProcessor | ConfigurationClassPostProcessor 对象 | 处理 Spring 配置类 |
| org.springframework.context.annotation.internalAutowiredAnnotationProcessor | AutowiredAnnotationBeanPostProcessor 对象 | 处理 @Autowired 以及 @Value注解 |
| org.springframework.context.annotation.internalCommonAnnotationProcessor | CommonAnnotationBeanPostProcessor 对象 | （条件激活）处理 JSR-250 注解，如 @PostConstruct 等 |
| org.springframework.context.event.internalEventListenerProcessor | EventListenerMethodProcessor对象 | 处理标注 @EventListener 的Spring 事件监听方法 |
以下是AnnotationConfigUtils的registerAnnotationConfigProcessors方法定义这些BeanDefintion的过程：
// AnnotationConfigUtils定义的BeanDefintion
// org.springframework.context.annotation.AnnotationConfigUtils#registerAnnotationConfigProcessors(org.springframework.beans.factory.support.BeanDefinitionRegistry, java.lang.Object)
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, Object source) {
DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
}
Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<BeanDefinitionHolder>(8);
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition();
try {
def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
AnnotationConfigUtils.class.getClassLoader()));
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
}
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}
return beanDefs;
}
使用AbstractApplicationContext定义的BeanDefinition
| Bean 名称 | Bean 实例 | 使用场景 |
|---|---|---|
| environment | Environment 对象 | 外部化配置以及 Profiles |
| systemProperties | java.util.Properties 对象 | Java 系统属性 |
| systemEnvironment | java.util.Map 对象 | 操作系统环境变量 |
| messageSource | MessageSource 对象 | 国际化文案 |
| lifecycleProcessor | LifecycleProcessor 对象 | Lifecycle Bean 处理器 |
| applicationEventMulticaster | ApplicationEventMulticaster 对象 | Spring 事件广播器 |
以下是AbstractApplicationContext的prepareBeanFactory、initMessageSource方法定义这些BeanDefintion的过程：
// 注册一些beanDefinatiton
// org.springframework.context.support.AbstractApplicationContext#prepareBeanFactory
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Register early post-processor for detecting inner beans as ApplicationListeners.
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// Register default environment beans.
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
// 注册国际化相关
// org.springframework.context.support.AbstractApplicationContext#initMessageSource
protected void initMessageSource() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
// Make MessageSource aware of parent MessageSource.
if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
if (hms.getParentMessageSource() == null) {
// Only set parent context as parent MessageSource if no parent MessageSource
// registered already.
hms.setParentMessageSource(getInternalParentMessageSource());
}
}
if (logger.isDebugEnabled()) {
logger.debug("Using MessageSource [" + this.messageSource + "]");
}
}
else {
// Use empty MessageSource to be able to accept getMessage calls.
DelegatingMessageSource dms = new DelegatingMessageSource();
dms.setParentMessageSource(getInternalParentMessageSource());
this.messageSource = dms;
beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
"': using default [" + this.messageSource + "]");
}
}
}
加载注册好的bean-容器的refresh()方法
beandefination定义完之后，在AbstractApplicationContext的refresh()调用invokeBeanFactoryPostProcessors，将bean初始化。
// org.springframework.context.support.AbstractApplicationContext#refresh
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
详情请看springIOC容器经典启动过程：spring系列-注解驱动原理及源码-spring容器创建流程
二、依赖注入的依赖来源
1、依赖查找的所有来源
同上
2、非Spring容器管理的对象
注入时机
在springIOC启动的refresh()中，调用prepareBeanFactory方法，prepareBeanFactory中注册了这样几个依赖：
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
使用时机
在依赖注入的DefaultListableBeanFactory类的doResolveDependency方法中：
// 关键方法：findAutowireCandidates
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
if (matchingBeans.isEmpty()) {
if (isRequired(descriptor)) {
raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
}
return null;
}
// org.springframework.beans.factory.support.DefaultListableBeanFactory#findAutowireCandidates
protected Map<String, Object> findAutowireCandidates(
String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {
String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this, requiredType, true, descriptor.isEager());
Map<String, Object> result = new LinkedHashMap<String, Object>(candidateNames.length);
// 这里的resolvableDependencies 就是上面注册的ResolvableDependency
for (Class<?> autowiringType : this.resolvableDependencies.keySet()) {
if (autowiringType.isAssignableFrom(requiredType)) {
Object autowiringValue = this.resolvableDependencies.get(autowiringType);
autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
if (requiredType.isInstance(autowiringValue)) {
result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
break;
}
}
}
for (String candidate : candidateNames) {
if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) {
addCandidateEntry(result, candidate, descriptor, requiredType);
}
}
if (result.isEmpty() && !indicatesMultipleBeans(requiredType)) {
// Consider fallback matches if the first pass failed to find anything...
DependencyDescriptor fallbackDescriptor = descriptor.forFallbackMatch();
for (String candidate : candidateNames) {
if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, fallbackDescriptor)) {
addCandidateEntry(result, candidate, descriptor, requiredType);
}
}
if (result.isEmpty()) {
// Consider self references as a final pass...
// but in the case of a dependency collection, not the very same bean itself.
for (String candidate : candidateNames) {
if (isSelfReference(beanName, candidate) &&
(!(descriptor instanceof MultiElementDescriptor) || !beanName.equals(candidate)) &&
isAutowireCandidate(candidate, fallbackDescriptor)) {
addCandidateEntry(result, candidate, descriptor, requiredType);
}
}
}
}
return result;
}
再回过头来看prepareBeanFactory方法中注册时调用的registerResolvableDependency方法，我们发现确实是直接将k-v值放到resolvableDependencies中：
// org.springframework.beans.factory.support.DefaultListableBeanFactory#registerResolvableDependency
@Override
public void registerResolvableDependency(Class<?> dependencyType, Object autowiredValue) {
Assert.notNull(dependencyType, "Dependency type must not be null");
if (autowiredValue != null) {
if (!(autowiredValue instanceof ObjectFactory || dependencyType.isInstance(autowiredValue))) {
throw new IllegalArgumentException("Value [" + autowiredValue +
"] does not implement specified dependency type [" + dependencyType.getName() + "]");
}
this.resolvableDependencies.put(dependencyType, autowiredValue);
}
}
这四个对象没法用BeanFactory.getBean获取到？
这四个对象，虽然也是依赖注入到了IOC容器中，但是我们不能用BeanFactory.getBean的方式获取。
如果直接调用getBean，会报Bean找不到的错误-NoSuchBeanException。
实例
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.core.io.ResourceLoader;
import javax.annotation.PostConstruct;
/**
* 依赖来源示例
*/
public class DependencySourceDemo {
// 注入在 postProcessProperties 方法执行，早于 setter注入，也早于 @PostConstruct
@Autowired
private BeanFactory beanFactory;
@Autowired
private ResourceLoader resourceLoader;
@Autowired
private ApplicationContext applicationContext;
@Autowired
private ApplicationEventPublisher applicationEventPublisher;
// 由源码我们得出：后三个是同一个东西
@PostConstruct
public void initByInjection() {
System.out.println("beanFactory == applicationContext " + (beanFactory == applicationContext));
System.out.println("beanFactory == applicationContext.getBeanFactory() " + (beanFactory == applicationContext.getAutowireCapableBeanFactory()));
System.out.println("resourceLoader == applicationContext " + (resourceLoader == applicationContext));
System.out.println("ApplicationEventPublisher == applicationContext " + (applicationEventPublisher == applicationContext));
}
// 使用getBean 方法查找，是查不到的，只能使用@Autowired自动注入获取
@PostConstruct
public void initByLookup() {
getBean(BeanFactory.class);
getBean(ApplicationContext.class);
getBean(ResourceLoader.class);
getBean(ApplicationEventPublisher.class);
}
private <T> T getBean(Class<T> beanType) {
try {
return beanFactory.getBean(beanType);
} catch (NoSuchBeanDefinitionException e) {
System.err.println("当前类型" + beanType.getName() + " 无法在 BeanFactory 中查找!");
}
return null;
}
public static void main(String[] args) {
// 创建 BeanFactory 容器
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
// 注册 Configuration Class（配置类） -> Spring Bean
applicationContext.register(DependencySourceDemo.class);
// 启动 Spring 应用上下文
applicationContext.refresh();
// 依赖查找 DependencySourceDemo Bean
DependencySourceDemo demo = applicationContext.getBean(DependencySourceDemo.class);
// 显示地关闭 Spring 应用上下文
applicationContext.close();
}
}
执行结果：
beanFactory == applicationContext false
beanFactory == applicationContext.getBeanFactory() true
resourceLoader == applicationContext true
ApplicationEventPublisher == applicationContext true
当前类型org.springframework.beans.factory.BeanFactory 无法在 BeanFactory 中查找!
当前类型org.springframework.context.ApplicationContext 无法在 BeanFactory 中查找!
当前类型org.springframework.core.io.ResourceLoader 无法在 BeanFactory 中查找!
当前类型org.springframework.context.ApplicationEventPublisher 无法在 BeanFactory 中查找!
Disconnected from the target VM, address: ‘127.0.0.1:60775’, transport: ‘socket’
Process finished with exit code 0
三、各种bean的详细解释
1、自定义BeanDefinition注册流程
自定义的BeanDefinition是由BeanDefinitionRegistry进行注册的，BeanDefinitionRegistry接口提供了对BeanDefinition基本的增删改查接口：
public interface BeanDefinitionRegistry extends AliasRegistry {
void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException;
void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
boolean containsBeanDefinition(String beanName);
String[] getBeanDefinitionNames();
int getBeanDefinitionCount();
boolean isBeanNameInUse(String beanName);
}
BeanDefinitionRegistry的默认实现就是DefaultListableBeanFactory，我们看一下DefaultListableBeanFactory的bean注册方法——registerBeanDefinition：
// org.springframework.beans.factory.support.DefaultListableBeanFactory#registerBeanDefinition
@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) {
try {
// 对beanDefinition做校验，其实使用BeanDefinitionBuilder时，调用builder方法时做过校验
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
// 看BeanDefinition 是否已被注册
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
// 如果已经被注册，看BeanDefinition是否允许被覆盖，spring2.1被人为改成false
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + existingDefinition + "] bound.");
}
// 看角色是否相等，角色其实并没有具体含义
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isWarnEnabled()) {
logger.warn("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.isInfoEnabled()) {
logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
// put进去
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
// bean不存在
if (hasBeanCreationStarted()) {
// Bean是否已经开始创建？
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// 存beanDefinition信息，使用map存，所以name是唯一的。
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition); // 无序
this.beanDefinitionNames.add(beanName); // 有序，bean按顺序初始化
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
2、外部化配置的单体对象
外部化配置的单体对象无生命周期管理、无法实现延迟初始化Bean。
它是由SingletonBeanRegistry接口进行注册的，SingletonBeanRegistry接口实现了对singletonBean的处理，其默认实现是DefaultListableBeanFactory。
public interface SingletonBeanRegistry {
void registerSingleton(String beanName, Object singletonObject);
Object getSingleton(String beanName);
boolean containsSingleton(String beanName);
String[] getSingletonNames();
Object getSingletonMutex();
}
我们来看registerSingleton方法的实现：
// org.springframework.beans.factory.support.DefaultListableBeanFactory#registerSingleton
@Override
public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {
super.registerSingleton(beanName, singletonObject); // 调用父类的注册
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
if (!this.beanDefinitionMap.containsKey(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames.size() + 1);
updatedSingletons.addAll(this.manualSingletonNames);
updatedSingletons.add(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
if (!this.beanDefinitionMap.containsKey(beanName)) {
this.manualSingletonNames.add(beanName);
}
}
clearByTypeCache();
}
// org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#registerSingleton
@Override
public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
Object oldObject = this.singletonObjects.get(beanName);
if (oldObject != null) {
throw new IllegalStateException("Could not register object [" + singletonObject +
"] under bean name '" + beanName + "': there is already object [" + oldObject + "] bound");
}
addSingleton(beanName, singletonObject);
}
}
// org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#addSingleton
protected void addSingleton(String beanName, Object singletonObject) {
synchronized (this.singletonObjects) {
// 加锁，可重入
this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
我们再来看getBean的实现，我们发现，如果获取Singleton Bean获取到了，就不会走下面的逻辑了。如果没有获取到，就会获取普通的BeanDefination逻辑，这个逻辑会有一个将BeanDefination注册为Bean的逻辑，而Singleton Bean没有：
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName); // 获取Singleton Bean
if (sharedInstance != null && args == null) {
if (logger.isTraceEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
...
3、非Spring容器管理的对象——ResolvableDependency
通过：ConfigurableListableBeanFactory#registerResolvableDependency 进行注册。
这种对象无生命周期管理、无法实现延迟初始化Bean、无法通过依赖查找。
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import javax.annotation.PostConstruct;
/**
* ResolvableDependency 作为依赖来源
*/
public class ResolvableDependencySourceDemo {
@Autowired
private String value;
@PostConstruct
public void init() {
System.out.println(value);
}
public static void main(String[] args) {
// 创建 BeanFactory 容器
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
// 注册 Configuration Class（配置类） -> Spring Bean
applicationContext.register(ResolvableDependencySourceDemo.class);
applicationContext.addBeanFactoryPostProcessor(beanFactory -> {
// 注册 Resolvable Dependency
beanFactory.registerResolvableDependency(String.class, "Hello,World");
});
// 启动 Spring 应用上下文，会有注册BeanPostProcessor的回调
applicationContext.refresh();
// 显示地关闭 Spring 应用上下文
applicationContext.close();
}
}
四、外部化配置作为依赖来源
1、实例
使用外部化的配置文件作为依赖来源，获取依赖对象时，只能通过@Value获取。
@Configuration
@PropertySource(value = "META-INF/default.properties",encoding="UTF-8")
public class ExternalConfigurationDependencySourceDemo {
@Value("${user.id:-1}")
private Long id;
@Value("${usr.name}")
private String name;
@Value("${user.resource:classpath://default.properties}")
private Resource resource;
public static void main(String[] args) {
// 创建 BeanFactory 容器
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
// 注册 Configuration Class（配置类） -> Spring Bean
applicationContext.register(ExternalConfigurationDependencySourceDemo.class);
// 启动 Spring 应用上下文
applicationContext.refresh();
// 依赖查找 ExternalConfigurationDependencySourceDemo Bean
ExternalConfigurationDependencySourceDemo demo = applicationContext.getBean(ExternalConfigurationDependencySourceDemo.class);
System.out.println("demo.id = " + demo.id);
System.out.println("demo.name = " + demo.name);
System.out.println("demo.resource = " + demo.resource);
// 显示地关闭 Spring 应用上下文
applicationContext.close();
}
}
2、原理
AutowiredAnnotationBeanPostProcessor也会处理@Value注解：
public AutowiredAnnotationBeanPostProcessor() {
this.autowiredAnnotationTypes.add(Autowired.class);
this.autowiredAnnotationTypes.add(Value.class);
try {
this.autowiredAnnotationTypes.add((Class<? extends Annotation>)
ClassUtils.forName("javax.inject.Inject", AutowiredAnnotationBeanPostProcessor.class.getClassLoader()));
logger.info("JSR-330 'javax.inject.Inject' annotation found and supported for autowiring");
}
catch (ClassNotFoundException ex) {
// JSR-330 API not available - simply skip.
}
}
当进行依赖注入时：
// org.springframework.beans.factory.support.DefaultListableBeanFactory#doResolveDependency
public Object doResolveDependency(DependencyDescriptor descriptor, String beanName,
Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
try {
Object shortcut = descriptor.resolveShortcut(this);
if (shortcut != null) {
return shortcut;
}
Class<?> type = descriptor.getDependencyType();
// 此处的value值，就是@Value里面的表达式：${user.id}
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) {
if (value instanceof String) {
// 获取配置文件中的值
String strVal = resolveEmbeddedValue((String) value);
BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);
value = evaluateBeanDefinitionString(strVal, bd);
}
// org.springframework.beans.factory.support.AbstractBeanFactory#resolveEmbeddedValue
@Override
public String resolveEmbeddedValue(String value) {
if (value == null) {
return null;
}
String result = value;
// 此处的StringValueResolver ，是可以通过EmbeddedValueResolverAware回调的
for (StringValueResolver resolver : this.embeddedValueResolvers) {
result = resolver.resolveStringValue(result);
if (result == null) {
return null;
}
}
return result;
}
我们都知道，spring的aware接口都是一些回调接口：
public interface EmbeddedValueResolverAware extends Aware {
/**
* Set the StringValueResolver to use for resolving embedded definition values.
*/
void setEmbeddedValueResolver(StringValueResolver resolver);
}