前言
在读refresh(context);时，finishBeanFactoryInitialization(beanFactory);中beanFactory.preInstantiateSingletons();用于实例化剩余所有的non-lazy-init的单例。这里包含了前置处理器和后置处理器
这里面就用到了本文主题getBean(beanName);
下面具体看看这个方法的源码
类图
AbstractBeanFactory实现了BeanFactory中getBean(String name)
调用主流程
public Object getBean(String name) throws BeansException {
// 找到做事的方法doGetBean
return doGetBean(name, null, null, false);
}
解析做事的主方法doGetBean
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
// 转换bean为实际的名称
String beanName = transformedBeanName(name);
// 保存Bean实例的对象
Object beanInstance;
// Eagerly check singleton cache for manually registered singletons.
// 检查单例缓存是否有手动注册的单例，这里涉及到三级缓存
// 看详解1
Object sharedInstance = getSingleton(beanName);
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 + "'");
}
}
beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
// 如果我们已经在创建这个bean实例，则失败: 我们假设在循环引用中
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
// 检查此工厂中是否存在bean定义
// 获取父Bean工厂
BeanFactory parentBeanFactory = getParentBeanFactory();
// 从beanDefinitionMap里containsKey一下这个beanName ，不在则进入此条件
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
// 不在检查其父
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
// 类型检查是否获取实例不用于实际使用
if (!typeCheckOnly) {
// 将指定的bean标记为已创建 (或即将创建)
markBeanAsCreated(beanName);
}
StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate")
.tag("beanName", name);
try {
if (requiredType != null) {
beanCreation.tag("beanType", requiredType::toString);
}
// 获取合并后的BeanDefinition，详见详解2
RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
// 检查是否是抽象的，是抽象的报错
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
// 获取DependsOn
String[] dependsOn = mbd.getDependsOn();
// 有依赖的，要先初始化依赖的
if (dependsOn != null) {
// 循环处理依赖
for (String dep : dependsOn) {
// 判断是否已经依赖，循环依赖
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
// 注册依赖Bean
registerDependentBean(dep, beanName);
try {
// 先获取依赖的Bean
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// Create bean instance.
// 是否是单例的，创建Bean实例
if (mbd.isSingleton()) {
// 这里是个回调函数，先进入看getSingleton方法，看详解3
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
if (!StringUtils.hasLength(scopeName)) {
throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
}
Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new ScopeNotActiveException(beanName, scopeName, ex);
}
}
}
catch (BeansException ex) {
beanCreation.tag("exception", ex.getClass().toString());
beanCreation.tag("message", String.valueOf(ex.getMessage()));
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
finally {
beanCreation.end();
}
}
// 适配Bean实例。详看6
return adaptBeanInstance(name, beanInstance, requiredType);
}
详解1——Object sharedInstance = getSingleton(beanName);
public Object getSingleton(String beanName) {
// allowEarlyReference(应该创建早期引用)属性为true
return getSingleton(beanName, true);
}
检查已经实例化的单例，并且还允许对当前创建的单例进行早期引用 (解析循环引用)。
三级缓存：
- singletonObjects：单例对象的缓存
- earlySingletonObjects：早期单例对象的缓存
- singletonFactories：单例工厂的缓存
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
// Quick check for existing instance without full singleton lock
// 取单例，取到直接返回
Object singletonObject = this.singletonObjects.get(beanName);
// 没取到 且 正在创建
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
// 从早期单例对象取，取到直接返回
singletonObject = this.earlySingletonObjects.get(beanName);
// 没取到 且 需要创建早期引用
if (singletonObject == null && allowEarlyReference) {
// 加锁
synchronized (this.singletonObjects) {
// Consistent creation of early reference within full singleton lock
// 在加锁的情况下再次取单例，确定在这个过程中是否已经创建完成。取到直接返回
singletonObject = this.singletonObjects.get(beanName);
// 未取到
if (singletonObject == null) {
// 在加锁的情况下再次取早期单例，确定在这个过程中是否已创建早期单例对象。取到直接返回
singletonObject = this.earlySingletonObjects.get(beanName);
// 未取到
if (singletonObject == null) {
// 去单例工厂。未取到返回null
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
// 取到单例工厂
if (singletonFactory != null) {
// 创建一个单例对象
singletonObject = singletonFactory.getObject();
// 放入早期单例对象
this.earlySingletonObjects.put(beanName, singletonObject);
// 从工厂中移除
this.singletonFactories.remove(beanName);
}
}
}
}
}
}
// 有4中情况的返回 单例对象、早期单例对象、单例工厂、null
return singletonObject;
}
详看2——getObjectForBeanInstance(sharedInstance, name, beanName, null);
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
// 当前创建的Bean
String currentlyCreatedBean = this.currentlyCreatedBean.get();
// 不为空
if (currentlyCreatedBean != null) {
// 为给定的bean注册一个依赖的bean，在给定的bean被销毁之前要销毁
registerDependentBean(beanName, currentlyCreatedBean);
}
// 调用父类的方法
return super.getObjectForBeanInstance(beanInstance, name, beanName, mbd);
}
父类AbstractBeanFactory的getObjectForBeanInstance方法
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
// Don't let calling code try to dereference the factory if the bean isn't a factory.
// 如果bean不是工厂，请不要让调用代码尝试取消引用工厂。
if (BeanFactoryUtils.isFactoryDereference(name)) {
if (beanInstance instanceof NullBean) {
return beanInstance;
}
if (!(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass());
}
// 把isFactoryBean属性置为true
if (mbd != null) {
mbd.isFactoryBean = true;
}
// 返回工厂对象
return beanInstance;
}
// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
// 现在我们有一个Bean的实例，可能是普通Bean也可能是工厂Bean
// 如果他是一个FactoryBean，我们用它创建一个Bean实例，除非调用者想要一个工厂的引用
if (!(beanInstance instanceof FactoryBean)) {
// 不是工厂Bean直接返回实例对象
return beanInstance;
}
Object object = null;
if (mbd != null) {
mbd.isFactoryBean = true;
}
else {
// 从缓存里取
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
// 通过工厂Bean创建一个Bean
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
详解3——RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
// Quick check on the concurrent map first, with minimal locking.
// 在 concurrent map上快速检查，锁定最少
RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
if (mbd != null && !mbd.stale) {
return mbd;
}
// 没有再去调用获取。getBeanDefinition是在beanDefinitionMap里取。
return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
}
protected RootBeanDefinition getMergedBeanDefinition(String beanName, BeanDefinition bd)
throws BeanDefinitionStoreException {
// 再去调用获取
return getMergedBeanDefinition(beanName, bd, null);
}
获取详情，作用：如果给定bean的定义是子bean定义，则通过与父级合并来返回给定bean的RootBeanDefinition。
参数:
- beanName -bean定义的名称
- bd -原始bean定义 (Root/ChildBeanDefinition)
- containingBd -inner bean定义的包含bean定义，顶级bean定义的null
protected RootBeanDefinition getMergedBeanDefinition(
String beanName, BeanDefinition bd, @Nullable BeanDefinition containingBd)
throws BeanDefinitionStoreException {
synchronized (this.mergedBeanDefinitions) {
RootBeanDefinition mbd = null;
RootBeanDefinition previous = null;
// Check with full lock now in order to enforce the same merged instance.
// 在锁下检测为了强制执行相同的合并实例
if (containingBd == null) {
mbd = this.mergedBeanDefinitions.get(beanName);
}
// 定义没取到合并后 或 定义需要重新合并
if (mbd == null || mbd.stale) {
// 保留mdb对象
previous = mbd;
// 取父定义的名称 为空
if (bd.getParentName() == null) {
// Use copy of given root bean definition.
// 使用给定root bean 定义的拷贝
if (bd instanceof RootBeanDefinition) {
// 本身就是直接clone
mbd = ((RootBeanDefinition) bd).cloneBeanDefinition();
}
else {
// bd转为RootBeanDefinition
mbd = new RootBeanDefinition(bd);
}
}
// 有父定义的名称
else {
// Child bean definition: needs to be merged with parent.
// 子定义需要merged给父定义
BeanDefinition pbd;
try {
// 获取父BeanName
String parentBeanName = transformedBeanName(bd.getParentName());
// 与父名称不一样
if (!beanName.equals(parentBeanName)) {
// 合并
pbd = getMergedBeanDefinition(parentBeanName);
}
else {
// 得到父BeanFactory
BeanFactory parent = getParentBeanFactory();
if (parent instanceof ConfigurableBeanFactory) {
// 从父BeanFactory得到BeanDefinition
pbd = ((ConfigurableBeanFactory) parent).getMergedBeanDefinition(parentBeanName);
}
else {
throw new NoSuchBeanDefinitionException(parentBeanName,
"Parent name '" + parentBeanName + "' is equal to bean name '" + beanName +
"': cannot be resolved without a ConfigurableBeanFactory parent");
}
}
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanDefinitionStoreException(bd.getResourceDescription(), beanName,
"Could not resolve parent bean definition '" + bd.getParentName() + "'", ex);
}
// Deep copy with overridden values.
// 深拷贝覆盖值
mbd = new RootBeanDefinition(pbd);
mbd.overrideFrom(bd);
}
// Set default singleton scope, if not configured before.
// 设置默认单例范围 (如果之前未配置)。
if (!StringUtils.hasLength(mbd.getScope())) {
mbd.setScope(SCOPE_SINGLETON);
}
// A bean contained in a non-singleton bean cannot be a singleton itself.
// Let's correct this on the fly here, since this might be the result of
// parent-child merging for the outer bean, in which case the original inner bean
// definition will not have inherited the merged outer bean's singleton status.
if (containingBd != null && !containingBd.isSingleton() && mbd.isSingleton()) {
mbd.setScope(containingBd.getScope());
}
// Cache the merged bean definition for the time being
// (it might still get re-merged later on in order to pick up metadata changes)
// 暂时缓存合并的bean定义 (以后可能仍会重新合并以获取元数据更改)
if (containingBd == null && isCacheBeanMetadata()) {
this.mergedBeanDefinitions.put(beanName, mbd);
}
}
if (previous != null) {
// 复制相关的合并Bean定义缓存
copyRelevantMergedBeanDefinitionCaches(previous, mbd);
}
return mbd;
}
}
详解4——getSingleton()
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
// 先上锁，锁singletonObjects对象
synchronized (this.singletonObjects) {
// 缓存里取一下
Object singletonObject = this.singletonObjects.get(beanName);
// 没取到
if (singletonObject == null) {
// 判断是否正在销毁，默认属性为false
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while singletons of this factory are in destruction " +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {
logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
}
// 单例创建前回调
// 判断beanName在不在当前在创建检查中排除的bean名称缓存中
// 加入当前正在创建的bean的名称缓存
// 上面两个有一个失败false则抛BeanCurrentlyInCreationException异常
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
// 这个singletonFactory就是回调函数，getObject()就是调用回调函数
// 这里 getObject()返回是主流程中的return createBean(beanName, mbd, args);
// 详见4.1
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
throw ex;
}
}
catch (BeanCreationException ex) {
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
afterSingletonCreation(beanName);
}
if (newSingleton) {
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
详看4.1——createBean(beanName, mbd, args)
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isTraceEnabled()) {
logger.trace("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
// 确保此时bean类已实际解析，并在无法存储在共享合并bean定义中的动态解析类的情况下克隆bean定义。
// 解析Bean类，详见4.2
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
// 有解析到class 且 不是BeanClass 且 有BeanClassName
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
// 准备方法覆盖
try {
// 检查查找方法是否存在，并确定其重载状态
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
// 给BeanPostProcessors一个返回代理而不是目标bean实例的机会。详看4.3
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isTraceEnabled()) {
logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
详看4.2——resolveBeanClass(mbd, beanName);
解析Bean类
protected Class<?> resolveBeanClass(RootBeanDefinition mbd, String beanName, Class<?>... typesToMatch)
throws CannotLoadBeanClassException {
try {
// 是否存在Bean类
if (mbd.hasBeanClass()) {
// 直接返回
return mbd.getBeanClass();
}
// 有安全策略
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged((PrivilegedExceptionAction<Class<?>>)
() -> doResolveBeanClass(mbd, typesToMatch), getAccessControlContext());
}
else {
// 做解析Bean类操作
return doResolveBeanClass(mbd, typesToMatch);
}
}
catch (PrivilegedActionException pae) {
ClassNotFoundException ex = (ClassNotFoundException) pae.getException();
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (ClassNotFoundException ex) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (LinkageError err) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), err);
}
}
做解析动作
private Class<?> doResolveBeanClass(RootBeanDefinition mbd, Class<?>... typesToMatch)
throws ClassNotFoundException {
// 获取类加载器
ClassLoader beanClassLoader = getBeanClassLoader();
// 动态类加载器
ClassLoader dynamicLoader = beanClassLoader;
// 新的解析标志
boolean freshResolve = false;
// 处理类型匹配
if (!ObjectUtils.isEmpty(typesToMatch)) {
// When just doing type checks (i.e. not creating an actual instance yet),
// use the specified temporary class loader (e.g. in a weaving scenario).
ClassLoader tempClassLoader = getTempClassLoader();
if (tempClassLoader != null) {
dynamicLoader = tempClassLoader;
freshResolve = true;
if (tempClassLoader instanceof DecoratingClassLoader) {
DecoratingClassLoader dcl = (DecoratingClassLoader) tempClassLoader;
for (Class<?> typeToMatch : typesToMatch) {
dcl.excludeClass(typeToMatch.getName());
}
}
}
}
// 获取类全名
String className = mbd.getBeanClassName();
if (className != null) {
// 评估bean定义中包含的给定字符串，有可能将其解析为表达式
Object evaluated = evaluateBeanDefinitionString(className, mbd);
// 是否是类全名
if (!className.equals(evaluated)) {
// A dynamically resolved expression, supported as of 4.2...
// 一个动态解析的表达式
if (evaluated instanceof Class) {
return (Class<?>) evaluated;
}
else if (evaluated instanceof String) {
className = (String) evaluated;
freshResolve = true;
}
else {
throw new IllegalStateException("Invalid class name expression result: " + evaluated);
}
}
// 是一个新的解析
if (freshResolve) {
// When resolving against a temporary class loader, exit early in order
// to avoid storing the resolved Class in the bean definition.
if (dynamicLoader != null) {
try {
// 使用动态的类加载器加载类
return dynamicLoader.loadClass(className);
}
catch (ClassNotFoundException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Could not load class [" + className + "] from " + dynamicLoader + ": " + ex);
}
}
}
// 反射出类
return ClassUtils.forName(className, dynamicLoader);
}
}
// Resolve regularly, caching the result in the BeanDefinition...
// 解析，将结果缓存在BeanDefinition中，看下面
return mbd.resolveBeanClass(beanClassLoader);
}
mbd.resolveBeanClass(beanClassLoader);解析
public Class<?> resolveBeanClass(@Nullable ClassLoader classLoader) throws ClassNotFoundException {
// 得到类名
String className = getBeanClassName();
if (className == null) {
return null;
}
// 详看4.3 获取类
Class<?> resolvedClass = ClassUtils.forName(className, classLoader);
this.beanClass = resolvedClass;
return resolvedClass;
}
获取类
public static Class<?> forName(String name, @Nullable ClassLoader classLoader)
throws ClassNotFoundException, LinkageError {
Assert.notNull(name, "Name must not be null");
// 解析原始类名，从primitiveTypeNameMap里取一下
Class<?> clazz = resolvePrimitiveClassName(name);
if (clazz == null) {
// 从通用缓存里取一下
clazz = commonClassCache.get(name);
}
if (clazz != null) {
return clazz;
}
// "java.lang.String[]" style arrays
// 一种数组风格
if (name.endsWith(ARRAY_SUFFIX)) {
String elementClassName = name.substring(0, name.length() - ARRAY_SUFFIX.length());
Class<?> elementClass = forName(elementClassName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
// "[Ljava.lang.String;" style arrays
// 一种数组风格
if (name.startsWith(NON_PRIMITIVE_ARRAY_PREFIX) && name.endsWith(";")) {
String elementName = name.substring(NON_PRIMITIVE_ARRAY_PREFIX.length(), name.length() - 1);
Class<?> elementClass = forName(elementName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
// "[[I" or "[[Ljava.lang.String;" style arrays
// 一种数组风格
if (name.startsWith(INTERNAL_ARRAY_PREFIX)) {
String elementName = name.substring(INTERNAL_ARRAY_PREFIX.length());
Class<?> elementClass = forName(elementName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
ClassLoader clToUse = classLoader;
// 类加载器为空
if (clToUse == null) {
clToUse = getDefaultClassLoader();
}
try {
// 反射出来实例
return Class.forName(name, false, clToUse);
}
catch (ClassNotFoundException ex) {
int lastDotIndex = name.lastIndexOf(PACKAGE_SEPARATOR);
if (lastDotIndex != -1) {
String nestedClassName =
name.substring(0, lastDotIndex) + NESTED_CLASS_SEPARATOR + name.substring(lastDotIndex + 1);
try {
return Class.forName(nestedClassName, false, clToUse);
}
catch (ClassNotFoundException ex2) {
// Swallow - let original exception get through
}
}
throw ex;
}
}
详看4.3——resolveBeforeInstantiation(beanName, mbdToUse)
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
// 没有在实例前解决
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
// 确保bean类实际上在这一点上得到解决。
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
// 确定目标类型
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
// 实例化前应用Bean Post处理器 重要
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
// 初始化后应用Bean Post处理器
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}
实例化前应用Bean Post处理器，前置处理器
protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
Object result = bp.postProcessBeforeInstantiation(beanClass, beanName);
if (result != null) {
return result;
}
}
return null;
}
初始化后应用Bean Post处理器
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
详看5——doCreateBean(beanName, mbdToUse, args);
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
// 实例化一个bean
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
// 先从第三级缓存移除
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {
if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
if (earlySingletonExposure) {
Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
// 解析的bean类 (如果没有，则为null)
Class<?> beanClass = resolveBeanClass(mbd, beanName);
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
}
// 获取实例供应商
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
// 获取factoryMethodName，不为空使用工厂方法实例化
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
// 重新创建相同bean时的快捷方式
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
return autowireConstructor(beanName, mbd, null, null);
}
else {
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
return instantiateBean(beanName, mbd);
}
详看6——adaptBeanInstance(name, beanInstance, requiredType);
适配Bean实例
<T> T adaptBeanInstance(String name, Object bean, @Nullable Class<?> requiredType) {
// Check if required type matches the type of the actual bean instance.
// 检查所需类型是否与实际bean实例的类型匹配。
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
// 类型转换器转换
Object convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return (T) convertedBean;
}
catch (TypeMismatchException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
// 不需要转换
return (T) bean;
}
