Spring容器初始化
本文使用的是Spring 5.1.7版本
寫在前面：我們看源碼一般有3種方式。
- 第一種直接用class文件，IDEA會幫我們反編譯成看得懂的java代碼
- 第二種是用maven的download Sources
- 第三種是直接下載源碼編譯
如果隨便看看，那么第二種就行了。如果想仔細研究，可以選第三種，這樣可以給代碼加注釋，或者修改一些東西等等。
Spring源碼構建
- 下載源碼（github）
- 安裝gradle
- 導入項目
- 編譯工程（順序：core->xom->context->beans->aspects->aop）
- 編譯方法：工程->tasks->compileTestJava
- 編譯完成后，新建一個測試module，用gradle的方式，build.gradle為：
group 'org.springframework'
version '5.1.21.BUILD-SNAPSHOT'
apply plugin: 'java'
sourceCompatibility = 1.8
repositories {
mavenCentral()
}
dependencies {
compile(project(":spring-context"))
testCompile group: 'junit', name: 'junit', version: '4.12'
}
如果運行報錯，需要設置IDEA。
需要將Preferences > Build, Execution, Deployment > Build Tools > Gradle > Runner里的 Delegate IDE build/run actions to gradle勾選上。
Spring IOC容器初始化的關鍵環節就在AbstractApplicationContext的refresh方法中。
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//第一步：刷新前的預處理
prepareRefresh();
// 第二步：獲取BeanFactory；加載BeanDefition並注冊到BeanDefitionRegistry
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 第三步：BeanFactory的預准備工作
prepareBeanFactory(beanFactory);
try {
// 第四步：BeanFactory准備工作完成之后進行的后置處理
postProcessBeanFactory(beanFactory);
// 第五步：實例化並調用實現了BeanFactoryPostProcessor接口的Bean
invokeBeanFactoryPostProcessors(beanFactory);
// 第六步：注冊BeanPostProcessor，在創建bean的前后等執行。
registerBeanPostProcessors(beanFactory);
// 第七步：初始化MessageSource組件（做國際化功能；消息綁定，消息解析）
initMessageSource();
// 第八步：初始化事件派發器
initApplicationEventMulticaster();
//第九步：提供給子類重寫，容器刷新的適合可以自定義邏輯
onRefresh();
// 第十步：注冊應用監聽器。就是注冊實現了ApplicationListener接口的監聽器bean
registerListeners();
// 第十一步：初始化所有剩下的非懶加載的單例bean，
//填充屬性
//初始化方法調用
//調用BeanPostProcessor對bean進行后置處理
finishBeanFactoryInitialization(beanFactory);
// 第十二步：完成context的刷新。主要是調用LifecycleProcessor的onRefresh方法，並且發布ContextRefreshedEvent事件
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();
}
}
}
接下來我們分析第二步中的兩個子流程：
2.1. 獲取BeanFactory子流程
時序圖如下：
2.2. BeanDefinition加載解析及注冊⼦流程
BeanDefinition加載流程入口在AbstractRefreshableApplicationContext#refreshBeanFactory ⽅法中，會調用到loadBeanDefinitions方法，這個方法最終會由XmlBeanDefinitionReader的loadBeanDefinitions方法來完成。然后會調用它自己的doLoadBeanDefinitions方法。
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//讀取xml信息，將xml信息保存到Document中
Document doc = doLoadDocument(inputSource, resource);
//解析doc，封裝到BeanDefinition對象並進行注冊
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
//省略部分代碼....
繼續跟蹤registerBeanDefinitions方法。
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//獲取已有的BeanDefinition的數量
int countBefore = getRegistry().getBeanDefinitionCount();
//注冊BeanDefinitions
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
//返回新注冊的BeanDefinition的數量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
它又交由documentReader來執行registerBeanDefinitions方法。documentReader接收后調用本類的doRegisterBeanDefinitions來執行。這個方法里我們需要關注parseBeanDefinitions.preProcessXml和postProcessXml都是留給子類實現的。
protected void doRegisterBeanDefinitions(Element root) {
//省略部分代碼...
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
跟蹤parseBeanDefinitions方法，可以看到由DefaultBeanDefinitionDocumentReader#parseDefaultElement在進行解析
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//import處理
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//alias處理
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//解析bean元素
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
//嵌套bean處理
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
最后跟蹤processBeanDefinition的代碼
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//解析bean元素為BeanDefinition,但是此時使用BeanDefinitionHolder又包裝了一層
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// 完成BeanDefinition的注冊
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
到這里就完成了BeanDefinition的注冊。我們發現，所謂的注冊就是把 XML 中定義的Bean信息封裝為BeanDefinition對象之后放⼊⼀個Map中。
this.beanDefinitionMap.put(beanName, beanDefinition);
簡略的時序圖如下：
接下來我們分析一下Bean創建的流程。Bean創建是在refresh主流程中的第十一步里面。
11.1 Bean創建子流程
我們進入finishBeanFactoryInitialization方法。
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
//省略部分代碼...
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// 實例化所有非懶加載的bean
beanFactory.preInstantiateSingletons();
}
跟蹤preInstantiateSingletons方法
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// 遍歷所有的beanName
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//如果是工廠bean，即實現了FactoryBean接口
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(
(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
//實例化當前bean
getBean(beanName);
}
}
}
//省略...
}
我們發現不管是工廠Bean，還是普通Bean都會調用getBean(beanName);方法。然后調用到doGetBean方法。
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
String beanName = transformedBeanName(name);
Object bean;
// 從緩存中拿
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 + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
//如果已經有創建過程中的同beanName的bean，拋異常
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// 從parentBeanFactory里找對應的bean
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
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);
}
}
if (!typeCheckOnly) {
//打一個已創建的標記
markBeanAsCreated(beanName);
}
try {
RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// 保證當前bean所依賴的bean的初始化
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);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
//創建bean
// 單例bean
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
//具體的創建bean邏輯
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);
}
//多例bean
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();
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);
}
});
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;
}
}
// 檢查所需類型是否與實際bean實例的類型匹配。
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return 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());
}
}
return (T) bean;
}
可以看到經過一些判斷和校驗，會調createBean方法去創建bean，然后調用doCreateBean去完成創建。
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//創建bean實例，但是尚未設置屬性
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
//允許后處理器修改合並的bean定義
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;
}
}
//急切地緩存單例，以便能夠解析循環引用
//即使由BeanFactoryAware等生命周期接口觸發。
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 {
//設置屬性
populateBean(beanName, mbd, instanceWrapper);
//應用初始化方法，調用BeanPostProcessor后置處理器
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;
}
在上述的方法中會先實例化一個bean，然后注入property里面配置的屬性，最后執行初始化相關方法。
簡單時序圖：
