【spring源码分析】加载bean过程（2）

在上文【spring源码分析】加载bean过程（1）,分析了单例bean的初始化过程，对于整个过程进行跟踪分析，本文我们对于一些细节进行分析。还是先回到AbstractAutowireCapableBeanFactory的doCreateBean方法

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
mbd.postProcessed = true;
}
}

// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isDebugEnabled()) {
logger.debug("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
return getEarlyBeanReference(beanName, mbd, bean);
}
});
}

// Initialize the bean instance.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
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<String>(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 " +
"'getBeanNamesOfType' 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;
}

属性注入

可以看到第41行代码populateBean方法，

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
PropertyValues pvs = mbd.getPropertyValues();

if (bw == null) {
if (!pvs.isEmpty()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
return;
}
}

// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of the bean before properties are set. This can be used, for example,
// to support styles of field injection.
boolean continueWithPropertyPopulation = true;

if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
continueWithPropertyPopulation = false;
break;
}
}
}
}

if (!continueWithPropertyPopulation) {
return;
}

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;
}

boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

if (hasInstAwareBpps || needsDepCheck) {
PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
if (hasInstAwareBpps) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
checkDependencies(beanName, mbd, filteredPds, pvs);
}
}

applyPropertyValues(beanName, mbd, bw, pvs);
}

先看下36-71行，是对于AutoWired，Resource等自动注入的处理。重点是autowireByName，autowireByType，ibp.postProcessPropertyValues方法，先通过名称或者类型获取相应的bean，再执行注入操作。

再看一下最后一行的applyPropertyValues方法

protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
if (pvs == null || pvs.isEmpty()) {
return;
}

MutablePropertyValues mpvs = null;
List<PropertyValue> original;

if (System.getSecurityManager() != null) {
if (bw instanceof BeanWrapperImpl) {
((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
}
}

if (pvs instanceof MutablePropertyValues) {
mpvs = (MutablePropertyValues) pvs;
if (mpvs.isConverted()) {
// Shortcut: use the pre-converted values as-is.
try {
bw.setPropertyValues(mpvs);
return;
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}
original = mpvs.getPropertyValueList();
}
else {
original = Arrays.asList(pvs.getPropertyValues());
}

TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

// Create a deep copy, resolving any references for values.
List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
boolean resolveNecessary = false;
for (PropertyValue pv : original) {
if (pv.isConverted()) {
deepCopy.add(pv);
}
else {
String propertyName = pv.getName();
Object originalValue = pv.getValue();
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
boolean convertible = bw.isWritableProperty(propertyName) &&
!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
// Possibly store converted value in merged bean definition,
// in order to avoid re-conversion for every created bean instance.
if (resolvedValue == originalValue) {
if (convertible) {
pv.setConvertedValue(convertedValue);
}
deepCopy.add(pv);
}
else if (convertible && originalValue instanceof TypedStringValue &&
!((TypedStringValue) originalValue).isDynamic() &&
!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
pv.setConvertedValue(convertedValue);
deepCopy.add(pv);
}
else {
resolveNecessary = true;
deepCopy.add(new PropertyValue(pv, convertedValue));
}
}
}
if (mpvs != null && !resolveNecessary) {
mpvs.setConverted();
}

// Set our (possibly massaged) deep copy.
try {
bw.setPropertyValues(new MutablePropertyValues(deepCopy));
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}

第41-63行，对于属性遍历做一次深层复制，其实就只是对于属性List添加

到一个新的List中，是为了能解析所有属性的引用。看一下第83行的代码

@Override
public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
throws BeansException {

List<PropertyAccessException> propertyAccessExceptions = null;
List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
for (PropertyValue pv : propertyValues) {
try {
// This method may throw any BeansException, which won't be caught
// here, if there is a critical failure such as no matching field.
// We can attempt to deal only with less serious exceptions.
setPropertyValue(pv);
}
catch (NotWritablePropertyException ex) {
if (!ignoreUnknown) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (NullValueInNestedPathException ex) {
if (!ignoreInvalid) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (PropertyAccessException ex) {
if (propertyAccessExceptions == null) {
propertyAccessExceptions = new LinkedList<PropertyAccessException>();
}
propertyAccessExceptions.add(ex);
}
}

// If we encountered individual exceptions, throw the composite exception.
if (propertyAccessExceptions != null) {
PropertyAccessException[] paeArray =
propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]);
throw new PropertyBatchUpdateException(paeArray);
}
}

第13行setPropertyValue方法

@Override
public void setPropertyValue(String propertyName, Object value) throws BeansException {
BeanWrapperImpl nestedBw;
try {
nestedBw = getBeanWrapperForPropertyPath(propertyName);
}
catch (NotReadablePropertyException ex) {
throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
"Nested property in path '" + propertyName + "' does not exist", ex);
}
PropertyTokenHolder tokens = getPropertyNameTokens(getFinalPath(nestedBw, propertyName));
nestedBw.setPropertyValue(tokens, new PropertyValue(propertyName, value));
}

最后看一下setPropertyValue方法，由于篇幅限制截取了核心部分

final Method writeMethod = (pd instanceof GenericTypeAwarePropertyDescriptor ?
((GenericTypeAwarePropertyDescriptor) pd).getWriteMethodForActualAccess() :
pd.getWriteMethod());
if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) {
if (System.getSecurityManager()!= null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
writeMethod.setAccessible(true);
return null;
}
});
}
else {
writeMethod.setAccessible(true);
}
}

主要的流程：

（1）拿到写方法并将方法的可见性设置为true

（2）拿到Value值，对Bean通过反射调用写方法

这样完成了对于Bean属性值的设置。

Aware注入

回到doCreateBean方法的第43行initializeBean(beanName, exposedObject, mbd)方法，对于bean进行一些初始化处理。

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);
}

try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}

if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}

看一下上面第5行的实现：

private void invokeAwareMethods(final String beanName, final Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}

在使用Spring的时候我们将自己的Bean实现BeanNameAware接口、BeanFactoryAware接口等，依赖容器帮我们注入当前Bean的名称或者Bean工厂。如果bean是BeanNameAware接口的实现类会调用setBeanName方法、如果bean是BeanClassLoaderAware接口的实现类会调用setBeanClassLoader方法、如果是BeanFactoryAware接口的实现类会调用setBeanFactory方法，注入对应的属性值。

postProcessBeforeInitialization方法

上面initializeBean方法再看17行其实现：

@Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {

Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessBeforeInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}

遍历每个BeanPostProcessor接口实现，调用postProcessBeforeInitialization方法

调用初始化方法

还是上面initializeBean方法，再看21行其实现：

protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
throws Throwable {

boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isDebugEnabled()) {
logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
@Override
public Object run() throws Exception {
((InitializingBean) bean).afterPropertiesSet();
return null;
}
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
((InitializingBean) bean).afterPropertiesSet();
}
}

if (mbd != null) {
String initMethodName = mbd.getInitMethodName();
if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}

这里做了2件事：

1.判断bean是否实现InitializingBean，如果是的话强制转换为InitializingBean，调用afterPropertiesSet方法。

2.取bean配置的init-method方法，如果有的话通过反射调用。

调用postProcessAfterInitialization方法

依然是上面initializeBean方法，再看29行其实现：

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {

Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessAfterInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}

@Override
public void destroyBean(Object existingBean) {
new DisposableBeanAdapter(existingBean, getBeanPostProcessors(), getAccessControlContext()).destroy();
}

注册销毁方法

见最初doCreateBean的registerDisposableBeanIfNecessary(beanName, bean, mbd);

protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
if (mbd.isSingleton()) {
// Register a DisposableBean implementation that performs all destruction
// work for the given bean: DestructionAwareBeanPostProcessors,
// DisposableBean interface, custom destroy method.
registerDisposableBean(beanName,
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
}
else {
// A bean with a custom scope...
Scope scope = this.scopes.get(mbd.getScope());
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope '" + mbd.getScope() + "'");
}
scope.registerDestructionCallback(beanName,
new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
}
}
}

注册销毁方法需要满足的条件：

1.如果bean是DisposableBean的实现类，调用destroy()方法

2.如果bean有配置destroy-method属性，则调用对应的方法

满足上述条件之一，便会注册该bean的销毁方法。

总结

最后用一张图总结一下spring初始化bean的过程：