一、问题剖析
1.spring 容器的启动过程，启动期间都做了什么？什么时候创立单实例 bean？
2.ioc 是如何创立这些单实例 bean，是如何治理的？保留在哪里？
二、Debug 剖析
ClassPathXmlApplicationContext 的继承树
1. 创立 spring 容器，读取配置文件，类门路下加载配置文件
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");2. 最先加载的应该是动态初始化块，它会随着类的加载而加载
static {
// 在 WebLogic 8.1 中，在应用程序敞开时，紧急加载 ContextCLosedEvent 类以防止奇怪的类加载器问题。ContextClosedEvent.class.getName();}3. 调用 ClassPathXmlApplicationContext 的构造方法
/**
* 创立一个新的 classPathXmlApplicationcontext，从给定的 XML 文件加载定义，并主动刷新该 ontext。* @param applicationContext.xml
* 如果上下文创立失败，@抛出 BeansException
*/
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
// 调用类中其余结构
this(new String[] {configLocation}, true, null);
}4. 参数解析
| 参数名 | 参数值 |
|---|---|
| String[] configLocations | qpplicationContext.xml |
| refresh | true |
| parent | null |
/**
* 创立一个新的 classPathXmlApplicationContextwith 给定的父类，从给定的 XML 文件加载定义。* @param configLocations 资源地位数组
* @param refresh 是否主动刷新上下文
* 加载所有 bean 定义并创立所有单例。或者，在进一步的 configuri 之后手动调用刷新康泰克斯的
* @param 父上下文后手动调用刷新
* 如果上下文创立失败，@抛出 BeansException
* @see #refresh()
*/
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
// 1. 初始化父类
super(parent);
// 2. 设置本地的配置信息
setConfigLocations(configLocations);
// 3. 实现 Spring 容器的初始化
if (refresh) { //true 进入 refresh 办法
refresh(); // 所有单实例创立实现}
}5.refresh()解析
synchronized (this.startupShutdownMonitor) {
// 筹备此上下文以进行刷新
prepareRefresh();
// spring 解析 xml 配置文件，将要创立的所有 bean 的配置信息保存起来
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();5.1 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()解析
5.1.1 obtainFreshBeanFactory();
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {refreshBeanFactory(); // 刷新 beanFactory
return getBeanFactory();}5.1.2 refreshBeanFactory();
// 对上下文的底层 bean 工厂执行一次理论刷新，敞开上一个 bean 工厂 (如果有的话) 和为上下文生命周期的下一阶段初始化 afreshbean 工厂。if (hasBeanFactory()) { // 判断是否曾经创立 beanFactory 如果存在 beanFactory 则销毁并敞开
destroyBeans();
closeBeanFactory();}
try {DefaultListableBeanFactory beanFactory = createBeanFactory();// 创立一个新的 beanFactory
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);// 通过 beanFactory 加载 beanDefinition
synchronized (this.beanFactoryMonitor) {this.beanFactory = beanFactory;// 对 beanFactory 进行从新赋值。}
}
catch (IOException ex) {throw new ApplicationContextException("I/O error parsing bean definition source for" + getDisplayName(), ex);
}5.1.3 createBeanFactory()
protected DefaultListableBeanFactory createBeanFactory() {// 传入这个 context 的父 context 外部的 beanFactory
return new DefaultListableBeanFactory(getInternalParentBeanFactory());// 由此可见这个 context 外部的 beanFacotry5.2 解析完 xml 后
// 筹备在此上下文中应用的 bean 工厂
prepareBeanFactory(beanFactory);
try {
// 容许在上下文子类中对 bean 工厂进行后处理
postProcessBeanFactory(beanFactory);
// 调用上下文中注册为 bean 的工厂处理器
invokeBeanFactoryPostProcessors(beanFactory);
// 注册拦挡 bean 创立的 bean 处理器
registerBeanPostProcessors(beanFactory);
// 初始化消息来源, 用来反对国际化性能
initMessageSource();
// 初始化多事件派发器
initApplicationEventMulticaster();
// 初始化特定上下文子类中的其余专门化 bean，专门留给子类的办法
onRefresh();
// 查看侦听器 bean 并注册它们注册监听器
registerListeners();
// 实例化所有残余的 (非提早 -init) 单例
finishBeanFactoryInitialization(beanFactory);5.3 finishBeanFactoryInitialization(beanFactory)实现单实例 bean 创立;
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// 初始化类型转换的组件服务（次要用于自定义类型转化）if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
// 如果没有 bean 前期解决
//(例如 PropertyPlaceholderConfigurer bean)之前注册任何:
// 此时，次要用于解析正文属性值。if (!beanFactory.hasEmbeddedValueResolver()) {beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// 初始化加载时的 Autowire
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {getBean(weaverAwareName);
}
// 停止使用长期类加载器进行类型匹配
beanFactory.setTempClassLoader(null);
// 容许缓存所有 bean 定义元数据，不冀望进一步更改
beanFactory.freezeConfiguration();
// 实例化所有残余的 (非提早 -init) 单单实例 bean
beanFactory.preInstantiateSingletons();}beanFactory.preInstantiateSingletons()解析
// 日志记录
if (logger.isTraceEnabled()) {logger.trace("Pre-instantiating singletons in" + this);
}
// 迭代一个正本以容许 init 办法注册新的 bean 定义。// 尽管这可能不是惯例工厂疏导程序的一部分，但它在其余方面工作得很好。//beanDefinitionNames 所有定义 bean 的名字
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// 按程序初始化所有非懒加载的单实例 bean
for (String beanName : beanNames) {
// 依据 bean 的 id 获取到 bean 的具体定义信息
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 判断 bean 不是一个形象的、非懒加载的单实例 bean，所有这是 ioc 中 bean 的默认个性
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
// 如果该 bean 是工厂 bean，实现了 FactoryBean 接口的 bean，就进入判断
if (isFactoryBean(beanName)) {Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {final 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 {getBean(beanName); // 因为我并没有应用工厂创立 bean，所以来到这行
}
}
}getBean(beanName):bean 创立的细节
@Override
public Object getBean(String name) throws BeansException {
// 重写 BeanFactory 的办法
return doGetBean(name, null, null, false); // 调用了 doGetBean 接口
}doGetBean(name, null, null, false)：bean 创立的细节（重点）
参数
| 参数名 | 参数值 |
|---|---|
| name | bean 对象名称 |
| requiredType | null |
| args | null |
| typeCheckOnly | false |
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
// 先拿到要创立的 bean 名称
final String beanName = transformedBeanName(name);
Object bean;
// 从曾经注册的单实例 bean 外面查看有没有这个 bean
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) { // 缓存里有则走上面的代码
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 { // 第一次创立 bean 是没有的，所有走到这
// 如果咱们曾经创立了这个 bean 实例，则会失败: 咱们假如在循环援用中。if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);
}
// 查看父工厂中是否存在 bean 定义。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) { //typeCheckOnly false
// 标记 bean 的状态为曾经被创立，为了避免多线程并发创立 bean
markBeanAsCreated(beanName);
}
try {
// 获取合并后的 bean 的定义信息
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// 拿到以后 bean 创立之前所须要提前创立创立的 bean，depends-on 属性，调用依赖关系设置，如果有此属性就循环创立 deponds-on 属性依赖的 bean
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);
}
}
}
// 如果是单例，创立 bean
if (mbd.isSingleton()) {
// getSington 办法里创立 bean
sharedInstance = getSingleton(beanName, () -> {
try {
//bean 的创立次要办法
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);
}getSingleton(beanName, () -> {} 细节
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
// 先从单实例对象中将这些 beanget 进去
Object singletonObject = this.singletonObjects.get(beanName);
singletonObjects 是一个 hashMap
// 依照对象的名字和对象实例缓存所有单实例 bean
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256); if (singletonObject == null) { // 第一次创立为 null。进入上面的办法
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 + "'");
}
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {this.suppressedExceptions = new LinkedHashSet<>();
}
try {
// 在这里利用了反射创立了单实例 bean
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// 让单例对象同时隐式地呈现
// 如果是，持续，因为异样表明状态。> 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) {
// 创立完单实例 bean 后调用此办法
addSingleton(beanName, singletonObject);
addSingleton(beanName, singletonObject)细节
protected void addSingleton(String beanName, Object singletonObject) {synchronized (this.singletonObjects) {
//singletonObjects 之前创立的 map 汇合，将 bean 对象退出到 map 中
// 所以，创立好的对象最终会保留在这个 map 中
this.singletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
} }
}
return singletonObject;
}
} 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, () -> {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.
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;
}
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {smartSingleton.afterSingletonsInstantiated();
}
}
}
}
// 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();}
}
总结
最终单实例 bean 对象保留 DefaultSingletonBeanRegistry 类中的 singletonObjects 属性
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);