getBean
这里便是bean初始化的核心逻辑。源码比较复杂，分开说。以getBean(String name)为例。AbstractBeanFactory.getBean:
代码语言：javascript复制@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}第二个参数表示bean的Class类型，第三个表示创建bean需要的参数，最后一个表示不需要进行类型检查。
beanName转化
代码语言：javascript复制final String beanName = transformedBeanName(name);这里是将FactoryBean的前缀去掉以及将别名转为真实的名字。
手动注册bean检测
前面注册环境一节说过，Spring其实手动注册了一些单例bean。这一步就是检测是不是这些bean。如果是，那么再检测是不是工厂bean，如果是返回其工厂方法返回的实例，如果不是返回bean本身。
代码语言：javascript复制Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}检查父容器
如果父容器存在并且存在此bean定义，那么交由其父容器初始化:
代码语言：javascript复制BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
//此方法其实是做了前面beanName转化的逆操作，因为父容器同样会进行转化操作
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);
}
}依赖初始化
bean可以由depends-on属性配置依赖的bean。Spring会首先初始化依赖的bean。
代码语言：javascript复制String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dependsOnBean : dependsOn) {
//检测是否存在循环依赖
if (isDependent(beanName, dependsOnBean)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" beanName "' and '" dependsOnBean "'");
}
registerDependentBean(dependsOnBean, beanName);
getBean(dependsOnBean);
}
}registerDependentBean进行了依赖关系的注册，这么做的原因是Spring在即进行bean销毁的时候会首先销毁被依赖的bean。依赖关系的保存是通过一个ConcurrentHashMap<String, Set>完成的，key是bean的真实名字。
Singleton初始化
虽然这里大纲是Singleton初始化，但是getBean方法本身是包括所有scope的初始化，在这里一次说明了。
代码语言：javascript复制if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
return createBean(beanName, mbd, args);
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}getSingleton方法
是否存在
首先会检测是否已经存在，如果存在，直接返回:
代码语言：javascript复制synchronized (this.singletonObjects) {
Object singletonObject = this.singletonObjects.get(beanName);
}所有的单例bean都保存在这样的数据结构中: ConcurrentHashMap<String, Object>。
bean创建
源码位于AbstractAutowireCapableBeanFactory.createBean，主要分为几个部分:
lookup-method检测
此部分用于检测lookup-method标签配置的方法是否存在:
代码语言：javascript复制RootBeanDefinition mbdToUse = mbd;
mbdToUse.prepareMethodOverrides();prepareMethodOverrides:
代码语言：javascript复制public void prepareMethodOverrides() throws BeanDefinitionValidationException {
// Check that lookup methods exists.
MethodOverrides methodOverrides = getMethodOverrides();
if (!methodOverrides.isEmpty()) {
Set<MethodOverride> overrides = methodOverrides.getOverrides();
synchronized (overrides) {
for (MethodOverride mo : overrides) {
prepareMethodOverride(mo);
}
}
}
}prepareMethodOverride:
代码语言：javascript复制protected void prepareMethodOverride(MethodOverride mo) {
int count = ClassUtils.getMethodCountForName(getBeanClass(), mo.getMethodName());
if (count == 0) {
throw new BeanDefinitionValidationException(
"Invalid method override: no method with name '" mo.getMethodName()
"' on class [" getBeanClassName() "]");
} else if (count == 1) {
// Mark override as not overloaded, to avoid the overhead of arg type checking.
mo.setOverloaded(false);
}
}InstantiationAwareBeanPostProcessor触发
在这里触发的是其postProcessBeforeInitialization和postProcessAfterInstantiation方法。
代码语言：javascript复制Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
return beanInstance;继续:
代码语言：javascript复制protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}从这里可以看出，如果InstantiationAwareBeanPostProcessor返回的不是空，那么将不会继续执行剩下的Spring初始化流程，此接口用于初始化自定义的bean，主要是在Spring内部使用。
doCreateBean
同样分为几部分。
创建(createBeanInstance)
关键代码:
代码语言：javascript复制BeanWrapper instanceWrapper = null;
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}createBeanInstance的创建过程又分为以下几种情况:
instantiateUsingFactoryMethod部分源码:
```java
beanInstance = this.beanFactory.getInstantiationStrategy().instantiate(
mbd, beanName, this.beanFactory, factoryBean, factoryMethodToUse, argsToUse);
```
getInstantiationStrategy返回的是CglibSubclassingInstantiationStrategy对象。此处instantiate实现也很简单，就是调用工厂方法的Method对象反射调用其invoke即可得到对象，SimpleInstantiationStrategy.
instantiate核心源码:
```java
@Override
public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner,
Object factoryBean, final Method factoryMethod, Object... args) {
return factoryMethod.invoke(factoryBean, args);
}
```MergedBeanDefinitionPostProcessor
触发源码:
代码语言：javascript复制synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
mbd.postProcessed = true;
}
}此接口也是Spring内部使用的，不管它了。
属性解析
入口方法: AbstractAutowireCapableBeanFactory.populateBean，它的作用是: 根据autowire类型进行autowire by name，by type 或者是直接进行设置，简略后的源码:
代码语言：javascript复制protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
//所有<property>的值
PropertyValues pvs = mbd.getPropertyValues();
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
//设值
applyPropertyValues(beanName, mbd, bw, pvs);
}autowireByName源码:
代码语言：javascript复制protected void autowireByName(
String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
//返回所有引用(ref="XXX")的bean名称
String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
for (String propertyName : propertyNames) {
if (containsBean(propertyName)) {
//从BeanFactory获取
Object bean = getBean(propertyName);
pvs.add(propertyName, bean);
registerDependentBean(propertyName, beanName);
}
}
}autowireByType也是同样的套路，所以可以得出结论: autowireByName和autowireByType方法只是先获取到引用的bean，真正的设值是在applyPropertyValues中进行的。
属性设置
Spring判断一个属性可不可以被设置(存不存在)是通过java bean的内省操作来完成的，也就是说，属性可以被设置的条件是此属性拥有public的setter方法，并且注入时的属性名应该是setter的名字。
初始化
此处的初始化指的是bean已经构造完成，执行诸如调用其init方法的操作。相关源码:
代码语言：javascript复制// Initialize the bean instance.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
}initializeBean:
代码语言：javascript复制protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
invokeAwareMethods(beanName, bean);
return null;
}
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
invokeInitMethods(beanName, wrappedBean, mbd);
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}主要的操作步骤一目了然。
getObjectForBeanInstance
位于AbstractBeanFactory，此方法的目的在于如果bean是FactoryBean，那么返回其工厂方法创建的bean，而不是自身。
Prototype初始化
AbstractBeanFactory.doGetBean相关源码:
代码语言：javascript复制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);
}beforePrototypeCreation
此方法用于确保在同一时刻只能有一个此bean在初始化。
createBean
和单例的是一样的，不在赘述。
afterPrototypeCreation
和beforePrototypeCreation对应的，你懂的。
总结
可以看出，初始化其实和单例是一样的，只不过单例多了一个是否已经存在的检查。
其它Scope初始化
其它就指的是request、session。此部分源码:
代码语言：javascript复制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 "'");
}
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);
}scopes是一个LinkedHashMap<String, Scope>，可以调用 ConfigurableBeanFactory定义的registerScope方法注册其值。
Scope接口继承体系:
根据socpe.get的注释，此方法如果找到了叫做beanName的bean，那么返回，如果没有，将调用ObjectFactory创建之。Scope的实现参考类图。
