參考資料：spring源碼深度解析
Spring版本：Spring-4.3.5-RELEASE
吐槽下，老外寫的東西真暈啊，像親媽一樣啰啰嗦嗦幫你考慮了各種情況，然后最好還不忘加一句：
如果你不滿意，還可以拓展?。。?1.spring 核心代碼
1.1 核心流程初始化過程
非常清晰的模板方法，每一個步驟封裝成一個具體的函數(shù)進行代理，職責清晰明了；
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//預熱，做準備工作
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//獲取內(nèi)部的bean factory
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
//預熱beanFactory
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//beanFactory在上下文中注冊bean，核心的代碼就在這里
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// bean創(chuàng)建的時候攔截并注冊bean處理器，這里只創(chuàng)建處理器，真正的創(chuàng)建是在getBean(..)方法里
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
// 用于支持國際化，比如一些日志的國際化匹配等；
initMessageSource();
// 為上下文初始化消息傳播工具
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 鉤子方法：額外的beans處理方法
onRefresh();
// Check for listener beans and register them.
// 注冊監(jiān)聽器
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 實例化非延時加載的bean單例
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// push beans創(chuàng)建完成的消息
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();
}
}
}
1.2 spring 類加載的基本類spring DefaultListableBeanFactory UML示意圖：
image.png
1.3 spring bean 創(chuàng)建過程
- 轉(zhuǎn)換beanName
- 嘗試從緩存中獲取單例
- bean本身的實例化
- 原型模式依賴檢測
- parentBeanFactory 檢測
- 將gernerecBeanDefinition 轉(zhuǎn)換成 RootBeanDefination
- 尋找依賴
- 根據(jù)scope 初始化(init)對應的bean
- 類型轉(zhuǎn)換
/**
* Return an instance, which may be shared or independent, of the specified bean.
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@SuppressWarnings("unchecked")
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
//轉(zhuǎn)換beanName，我們知道在spring中，bean factory的名稱都是類似于 &org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory
//因此獲取的時候需要進行轉(zhuǎn)換
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
// 嘗試從緩存中獲取單例
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
//實例化
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
// 檢測當前依賴的類是否正在創(chuàng)建，如果是，則拋出異常
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
// 如果bean配置不存在則只能去父工廠找
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
//轉(zhuǎn)換并合并BeanDefinition屬性
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
// 原型模式的bean需要循環(huán)檢測依賴 防止出現(xiàn)A->B->A 的循環(huán)依賴情況出現(xiàn)
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
getBean(dep);
}
}
// Create bean instance.
// 創(chuàng)建bean實例
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
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;
}
}
});
bean = 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);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
final 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, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
// 轉(zhuǎn)換bean類型
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
catch (TypeMismatchException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
1.4 spring事務隔離級別及事務傳播實現(xiàn)
- propagation_requierd(spring的事務默認是該級別)：如果當前沒有事務，就新建一個事務，如果已存在一個事務中，加入到這個事務中，這是最常見的選擇。
- propagation_supports：支持當前事務，如果沒有當前事務，就以非事務方法執(zhí)行。
- propagation_mandatory：使用當前事務，如果沒有當前事務，就拋出異常。
- propagation_required_new：新建事務，如果當前存在事務，把當前事務掛起。
- propagation_not_supported：以非事務方式執(zhí)行操作，如果當前存在事務，就把當前事務掛起。
- propagation_never：以非事務方式執(zhí)行操作，如果當前事務存在則拋出異常。
- propagation_nested：如果當前存在事務，則在嵌套事務內(nèi)執(zhí)行。如果當前沒有事務，則執(zhí)行與propagation_required類似的操作
* Create a TransactionStatus for an existing transaction.
*/
private TransactionStatus handleExistingTransaction(
TransactionDefinition definition, Object transaction, boolean debugEnabled)
throws TransactionException {
//若為非事務方式，則拋異常
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) {
throw new IllegalTransactionStateException(
"Existing transaction found for transaction marked with propagation 'never'");
}
// 若存在事務，掛起適當前事務
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) {
if (debugEnabled) {
logger.debug("Suspending current transaction");
}
// 掛起當前事務
Object suspendedResources = suspend(transaction);
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
return prepareTransactionStatus(
definition, null, false, newSynchronization, debugEnabled, suspendedResources);
}
// 掛起當前事務，并新建事務
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
if (debugEnabled) {
logger.debug("Suspending current transaction, creating new transaction with name [" +
definition.getName() + "]");
}
//掛起當前事務
SuspendedResourcesHolder suspendedResources = suspend(transaction);
try {
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
// 重新開啟事務
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
catch (RuntimeException beginEx) {
resumeAfterBeginException(transaction, suspendedResources, beginEx);
throw beginEx;
}
catch (Error beginErr) {
resumeAfterBeginException(transaction, suspendedResources, beginErr);
throw beginErr;
}
}
// 若當前事務存在，則嵌套執(zhí)行事務
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
if (!isNestedTransactionAllowed()) {
throw new NestedTransactionNotSupportedException(
"Transaction manager does not allow nested transactions by default - " +
"specify 'nestedTransactionAllowed' property with value 'true'");
}
if (debugEnabled) {
logger.debug("Creating nested transaction with name [" + definition.getName() + "]");
}
// 判定是否支持事務備份點
if (useSavepointForNestedTransaction()) {
// Create savepoint within existing Spring-managed transaction,
// through the SavepointManager API implemented by TransactionStatus.
// Usually uses JDBC 3.0 savepoints. Never activates Spring synchronization.
DefaultTransactionStatus status =
prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null);
// 創(chuàng)建備份點
status.createAndHoldSavepoint();
return status;
}
else {
// Nested transaction through nested begin and commit/rollback calls.
// Usually only for JTA: Spring synchronization might get activated here
// in case of a pre-existing JTA transaction.
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, null);
// 不支持備份點的情況下會新建事務
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
}
// Assumably PROPAGATION_SUPPORTS or PROPAGATION_REQUIRED.
if (debugEnabled) {
logger.debug("Participating in existing transaction");
}
if (isValidateExistingTransaction()) {
if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
Integer currentIsolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
if (currentIsolationLevel == null || currentIsolationLevel != definition.getIsolationLevel()) {
Constants isoConstants = DefaultTransactionDefinition.constants;
throw new IllegalTransactionStateException("Participating transaction with definition [" +
definition + "] specifies isolation level which is incompatible with existing transaction: " +
(currentIsolationLevel != null ?
isoConstants.toCode(currentIsolationLevel, DefaultTransactionDefinition.PREFIX_ISOLATION) :
"(unknown)"));
}
}
if (!definition.isReadOnly()) {
if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
throw new IllegalTransactionStateException("Participating transaction with definition [" +
definition + "] is not marked as read-only but existing transaction is");
}
}
}
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
}
2.1 一些干貨
2.1.1 aop注入的實現(xiàn)過程
doCreateBean中會暴露一個bean引用，用以處理循環(huán)引用；同時大家熟知的AOP就是通過getEarlyBeanReference(..)方法植入的；具體的，是在wrapIfNecessary(..) 方法中封裝了advice并創(chuàng)建了代理；
image.png
image.png
2.1.2 @Autowired注解的實現(xiàn)
image.png
doCreateBean(..)中的populateBean(..)方法，實現(xiàn)了基于@Autowired注解的實現(xiàn)，根據(jù)名稱或類型進行依賴的注入；
