原文出处： 五月的仓颉
原型Bean加载过程
之前的文章，分析了非懒加载的单例Bean整个加载过程，除了非懒加载的单例Bean之外，Spring中还有一种Bean就是原型（Prototype）的Bean，看一下定义方式：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="prototypeBean" class="org.xrq.action.PrototypeBean" scope="prototype" />
</beans>
原型Bean加载流程总得来说和单例Bean差不多，看一下不同之处，在AbstractBeanFactory的doGetBean的方法的这一步：
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);
}
第6行createBean是一样的，原型Bean实例化的主要区别就在于第6行，它是直接创建bean的，而单例bean我们再对比一下：
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory() {
public Object getObject() throws BeansException {
try {
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);
}
它优先会尝试getSington，即先尝试从singletonObjects中获取一下bean是否存在，如果存在直接返回singletonObjects中的bean对象。
接着，我们看到原型bean创建和单例bean创建的区别还在于第5行和第9行，先看第5行的代码：
protected void beforePrototypeCreation(String beanName) {
Object curVal = this.prototypesCurrentlyInCreation.get();
if (curVal == null) {
this.prototypesCurrentlyInCreation.set(beanName);
}
else if (curVal instanceof String) {
Set<String> beanNameSet = new HashSet<String>(2);
beanNameSet.add((String) curVal);
beanNameSet.add(beanName);
this.prototypesCurrentlyInCreation.set(beanNameSet);
}
else {
Set<String> beanNameSet = (Set<String>) curVal;
beanNameSet.add(beanName);
}
}
这段主要是说bean在创建前要把当前beanName设置到ThreadLocal中去，其目的是保证多线程不会同时创建同一个bean。接着看第9行的代码实现，即bean创建之后做了什么：
protected void afterPrototypeCreation(String beanName) {
Object curVal = this.prototypesCurrentlyInCreation.get();
if (curVal instanceof String) {
this.prototypesCurrentlyInCreation.remove();
}
else if (curVal instanceof Set) {
Set<String> beanNameSet = (Set<String>) curVal;
beanNameSet.remove(beanName);
if (beanNameSet.isEmpty()) {
this.prototypesCurrentlyInCreation.remove();
}
}
}
很好理解，就是把当前bean移除一下，这样其它线程就可以创建bean了。第11行的代码不看了，意思是如果bean是FactoryBean的实现类的话，调用getObject()方法获取真正的对象。
byName源码实现
Spring有为开发者提供Autowire（自动装配）的功能，自动装配最常用的就是byName和byType这两种属性。由于自动装配是为了解决对象注入导致的<property>过多的问题，因此很容易找到byName与byType的Spring源码实现应该在属性注入这一块，定位到属性注入的代码AbstractAutowireCapableBeanFactory的populateBean方法，直接截取重点：
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;
}
看到第6行~第8行判断是否byName形式，是就执行byName自动装配代码；第11行~第13行判断是否byType形式，是就执行byType自动装配代码。那么首先看一下第7行的byName代码实现：
protected void autowireByName(
String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
for (String propertyName : propertyNames) {
if (containsBean(propertyName)) {
Object bean = getBean(propertyName);
pvs.add(propertyName, bean);
registerDependentBean(propertyName, beanName);
if (logger.isDebugEnabled()) {
logger.debug("Added autowiring by name from bean name '" + beanName +
"' via property '" + propertyName + "' to bean named '" + propertyName + "'");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
"' by name: no matching bean found");
}
}
}
}
篇幅问题，代码不一层层跟了，逻辑梳理一下：
- 第4行，找到Bean中不是简单属性的属性，这句话有点绕，意思就是找到属性是对象类型的属性，但也不是所有的对象类型都会被找到，比如CharSequence类型、Number类型、Date类型、URL类型、URI类型、Locale类型、Class类型就会忽略，具体可见BeanUtils的isSimpleProperty方法
- 第5行~第7行，遍历所有被找到的属性，如果bean定义中包含了属性名，那么先实例化该属性名对应的bean
- 第9行registerDependentBean，注册一下当前bean的依赖bean，用于在某个bean被销毁前先将其依赖的bean销毁
其余代码都是一些打日志的，没什么好说的。
byType源码实现
上面说了byName的源码实现，接下来看一下byType源码实现：
protected void autowireByType(
String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
Set<String> autowiredBeanNames = new LinkedHashSet<String>(4);
String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
for (String propertyName : propertyNames) {
try {
PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
// Don't try autowiring by type for type Object: never makes sense,
// even if it technically is a unsatisfied, non-simple property.
if (!Object.class.equals(pd.getPropertyType())) {
MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
// Do not allow eager init for type matching in case of a prioritized post-processor.
boolean eager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass());
DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);
Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
if (autowiredArgument != null) {
pvs.add(propertyName, autowiredArgument);
}
for (String autowiredBeanName : autowiredBeanNames) {
registerDependentBean(autowiredBeanName, beanName);
if (logger.isDebugEnabled()) {
logger.debug("Autowiring by type from bean name '" + beanName + "' via property '" +
propertyName + "' to bean named '" + autowiredBeanName + "'");
}
}
autowiredBeanNames.clear();
}
}
catch (BeansException ex) {
throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
}
}
}
前面一样，到第10行都是找到Bean中属性是对象类型的属性。
接着就是遍历一下PropertyName，获取PropertyName对应的属性描述，注意一下16行的判断及其对应的注释：不要尝试自动装配Object类型，这没有任何意义，即使从技术角度看它是一个非简单的对象属性。
第18行~第20行跳过（没有太明白是干什么的），byType实现的源码主要在第21行的方法resolveDependency中，这个方法是AbstractAutowireCapableBeanFactory类的实现类DefaultListableBeanFactory中的方法：
public Object resolveDependency(DependencyDescriptor descriptor, String beanName,
Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
if (descriptor.getDependencyType().equals(ObjectFactory.class)) {
return new DependencyObjectFactory(descriptor, beanName);
}
else if (descriptor.getDependencyType().equals(javaxInjectProviderClass)) {
return new DependencyProviderFactory().createDependencyProvider(descriptor, beanName);
}
else {
return doResolveDependency(descriptor, descriptor.getDependencyType(), beanName, autowiredBeanNames, typeConverter);
}
}
这里判断一下要自动装配的属性是ObjectFactory.class还是javaxInjectProviderClass还是其他的，我们装配的是其他的，看一下12行的代码实现：
protected Object doResolveDependency(DependencyDescriptor descriptor, Class<?> type, String beanName,
Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) {
if (value instanceof String) {
String strVal = resolveEmbeddedValue((String) value);
BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);
value = evaluateBeanDefinitionString(strVal, bd);
}
TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
return converter.convertIfNecessary(value, type);
}
if (type.isArray()) {
...
}
else if (Collection.class.isAssignableFrom(type) && type.isInterface()) {
...
}
else if (Map.class.isAssignableFrom(type) && type.isInterface()) {
...
}
else {
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(type, "", descriptor);
}
return null;
}
if (matchingBeans.size() > 1) {
String primaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor);
if (primaryBeanName == null) {
throw new NoSuchBeanDefinitionException(type, "expected single matching bean but found " +
matchingBeans.size() + ": " + matchingBeans.keySet());
}
if (autowiredBeanNames != null) {
autowiredBeanNames.add(primaryBeanName);
}
return matchingBeans.get(primaryBeanName);
}
// We have exactly one match.
Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
if (autowiredBeanNames != null) {
autowiredBeanNames.add(entry.getKey());
}
return entry.getValue();
}
}
第四行结果是null不看了，为了简化代码Array装配、Collection装配、Map装配的代码都略去了，重点看一下普通属性的装配。首先是第25行获取一下自动装配的候选者：
protected Map<String, Object> findAutowireCandidates(
String beanName, Class requiredType, DependencyDescriptor descriptor) {
String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this, requiredType, true, descriptor.isEager());
Map<String, Object> result = new LinkedHashMap<String, Object>(candidateNames.length);
for (Class autowiringType : this.resolvableDependencies.keySet()) {
if (autowiringType.isAssignableFrom(requiredType)) {
Object autowiringValue = this.resolvableDependencies.get(autowiringType);
autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
if (requiredType.isInstance(autowiringValue)) {
result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
break;
}
}
}
for (String candidateName : candidateNames) {
if (!candidateName.equals(beanName) && isAutowireCandidate(candidateName, descriptor)) {
result.put(candidateName, getBean(candidateName));
}
}
return result;
}
代码逻辑整理一下：
- 首先获取候选者bean名称，通过DefaultListableBeanFactory的getBeanNamesForType方法，即找一下所有的Bean定义中指定Type的实现类或者子类
- 接着第7行~第16行的判断要自动装配的类型是不是要自动装配的纠正类型，这个在【Spring源码分析】非懒加载的单例Bean初始化前后的一些操作一文讲PrepareBeanFactory方法的时候有讲过，如果要自动装配的类型是纠正类型，比如是一个ResourceLoader，那么就会为该类型生成一个代理实例，具体可以看一下第10行的AutowireUtils.resolveAutowiringValue方法的实现
- 正常来说都是执行的第17行~第21行的代码，逐个判断查找一下beanName对应的BeanDefinition，判断一下是不是自动装配候选者，默认都是的，如果<bean>的autowire-candidate属性设置为false就不是
这样，拿到所有待装配对象的实现类或者子类的候选者，组成一个Map，Key为beanName，Value为具体的Bean。接着回看获取Bean之后的逻辑：
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
if (matchingBeans.isEmpty()) {
if (descriptor.isRequired()) {
raiseNoSuchBeanDefinitionException(type, "", descriptor);
}
return null;
}
if (matchingBeans.size() > 1) {
String primaryBeanName = determinePrimaryCandidate(matchingBeans, descriptor);
if (primaryBeanName == null) {
throw new NoSuchBeanDefinitionException(type, "expected single matching bean but found " +
matchingBeans.size() + ": " + matchingBeans.keySet());
}
if (autowiredBeanNames != null) {
autowiredBeanNames.add(primaryBeanName);
}
return matchingBeans.get(primaryBeanName);
}
// We have exactly one match.
Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
if (autowiredBeanNames != null) {
autowiredBeanNames.add(entry.getKey());
}
...
}
整理一下逻辑：
- 如果拿到的Map是空的且属性必须注入，抛异常
- 如果拿到的Map中有多个候选对象，判断其中是否有<bean>中属性配置为”primary=true”的，有就拿执行第13行~第15行的代码，没有就第8行的方法返回null，抛异常，这个异常的描述相信Spring用的比较多的应该比较熟悉
- 如果拿到的Map中只有一个候选对象，直接拿到那个
通过这样一整个流程，实现了byType自动装配，byType自动装配流程比较长，中间细节比较多，还需要多看看才能弄明白。
最后注意一点，即所有待注入的PropertyName–>PropertyValue映射拿到之后都只是放在MutablePropertyValues中，最后由AbstractPropertyAccessor类的setPropertyValues方法遍历并进行逐一注入。
通过FactoryBean获取Bean实例源码实现
我们知道可以通过实现FactoryBean接口，重写getObject()方法实现个性化定制Bean的过程，这部分我们就来看一下Spring源码是如何实现通过FactoryBean获取Bean实例的。代码直接定位到AbstractBeanFactory的doGetBean方法创建单例Bean这部分：
// Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory() {
public Object getObject() throws BeansException {
try {
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);
}
FactoryBean首先是个Bean且被实例化出来成为一个对象之后才能调用getObject()方法，因此还是会执行第3行~第16行的代码，这段代码之前分析过了就不说了。之后执行第17行的方法：
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
// Don't let calling code try to dereference the factory if the bean isn't a factory.
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}
// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
Object object = null;
if (mbd == null) {
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean factory = (FactoryBean) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
首先第5行~第7行判断一下是否beanName以”&”开头并且不是FactoryBean的实现类，不满足则抛异常，因为beanName以”&”开头是FactoryBean的实现类bean定义的一个特征。
接着判断第12行~第14行，如果：
- bean不是FactoryBean的实现类
- beanName以”&”开头
这两种情况，都直接把生成的bean对象返回出去，不会执行余下的流程。
最后流程走到第16行~第30行，最终调用getObject()方法实现个性化定制bean，先执行第28行的方法：
protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName, boolean shouldPostProcess) {
if (factory.isSingleton() && containsSingleton(beanName)) {
synchronized (getSingletonMutex()) {
Object object = this.factoryBeanObjectCache.get(beanName);
if (object == null) {
object = doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
}
return (object != NULL_OBJECT ? object : null);
}
}
else {
return doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
}
}
第1行~第11行的代码与第12行~第13行的代码最终都是一样的，调用了如下一段：
private Object doGetObjectFromFactoryBean(
final FactoryBean factory, final String beanName, final boolean shouldPostProcess)
throws BeanCreationException {
Object object;
try {
if (System.getSecurityManager() != null) {
AccessControlContext acc = getAccessControlContext();
try {
object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
public Object run() throws Exception {
return factory.getObject();
}
}, acc);
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
object = factory.getObject();
}
}
catch (FactoryBeanNotInitializedException ex) {
throw new BeanCurrentlyInCreationException(beanName, ex.toString());
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
}
// Do not accept a null value for a FactoryBean that's not fully
// initialized yet: Many FactoryBeans just return null then.
if (object == null && isSingletonCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(
beanName, "FactoryBean which is currently in creation returned null from getObject");
}
if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of the FactoryBean's object failed", ex);
}
}
return object;
}
第12行和第21行的代码，都一样，最终调用getObject()方法获取对象。回过头去看之前的getObjectFromFactoryBean方法，虽然if…else…逻辑最终都是调用了以上的方法，但是区别在于：
- 如果FactoryBean接口实现类的isSington方法返回的是true，那么每次调用getObject方法的时候会优先尝试从FactoryBean对象缓存中取目标对象，有就直接拿，没有就创建并放入FactoryBean对象缓存，这样保证了每次单例的FactoryBean调用getObject()方法后最终拿到的目标对象一定是单例的，即在内存中都是同一份；
- 如果FactoryBean接口实现类的isSington方法返回的是false，那么每次调用getObject方法的时候都会新创建一个目标对象。
