记录并分享一下本人学习spring源码的过程，有什么问题或者补充会持续更新。欢迎大家指正！
环境： spring5.X + idea
建议：学习过程中要开着源码一步一步过
Spring根据BeanDefinition创建单例对象
DefaultSingletonBeanRegister中getSingleton((String beanName, ObjectFactory<?> singletonFactory))
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName, ...);
}
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
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;
}
}
解析：
- getSingleton 方法中还是先要在单例池中获取将要被创建的对象是不是存在，不存在了才去创建。this.singletonObjects.get(beanName); 如果不存在Spring还会效验一下是不是正在被销毁，是则抛异常。this.singletonsCurrentlyInDestruction
- 一系列效验完成后开始正式创建对象的第一步
beforeSingletonCreation(beanName);
创建对象前要满足俩个条件inCreationCheckExclusions&&singletonsCurrentlyInCreation.add(beanName),当前这个Bean没有被排除，并且这个bean正在创建中。 - 通过
singletonFactory.getObject();回调createBean(beanName, mbd, args);
创建对象时先获取对应的BeanClass（通过反射创建对象），调用doCreateBean(beanName, mbdToUse, args);，这个方法中才是正儿八经的实例化对象
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
//....
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
//.............
// 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;
}
doCreateBean解析：
A. 创建对象：createBeanInstance(beanName, mbd, args);
- 通过工厂方法创建对象
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
- 通过默认的无参构造创建对象
instantiateBean(beanName, mbd);
B. 填充属性：populateBean(beanName, mbd, instanceWrapper); 也是就是Set注入(构造注入已经在创建对象时执行了，自动注入可以忽略)
- 注解属性赋值
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
解析：通过注解对属性填充使用了AutowiredAnnotationBeanPostProcessor实现所有操作，在postProcessProperties(pvs, bw.getWrappedInstance(), beanName);方法中真正实现。
- 标签方式属性赋值
if (pvs != null) {
applyPropertyValues(beanName, mbd, bw, pvs);
}
解析：从RootBeanDefinition中获取属性的List封装到PropertyValues中。
遍历ProperValues 把每个属性的值进行类型转换，最后再给bw设置得到的属性值。-> BeanWrapper.setProperValues(new MutablePropertyValues(deepCopy))。
自定义类型会通过beanFactory.getBean() 获取对应的对象，再走一遍doGetBean() -> createBean() -> doCreateBean()...
（JDK的类型会先封装TypeStringValues。自定义的类型会封装RuntimeBeanReference）
C. 初始化对象：initializeBean(beanName, exposedObject, mbd);
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
.......
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
......
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
解析：初始化分几个功能
1. Aware -> invokeAwareMethods(String beanName, Object bean)。spring提供的帮助我们获取Spring容器中对应的组件的相关信息。
2. BeanPostProcessorsBefore -> applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);已经创建好的对象初始化之前再次加工。
3. 初始化 -> invokeInitMethods(beanName, wrappedBean, mbd);包含了接口初始化((InitializingBean) bean).afterPropertiesSet();和自定义方法初始化invokeCustomInitMethod(beanName, bean, mbd);
4. BeanPostProcessorsAfter -> applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);已经创建好的对象初始化之后再次加工。
最后
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