前面提的基本上都是ApplicationContext的refresh方法，在分析的过程中bean容器的基本启动过程心中有了大体的了解，分析过程中，我们发现bean的实例化及加工相关的处理都在getBean方法中，一起看下getBean方法。
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
doGetBean的方法比较长，拆开分析
分析
- 从缓存中，或者获取手动注册的bean，也就是单例的bean已经被创建过了，那么直接获取。
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
getObjectForBeanInstance主要做了如下事情：
- 如果sharedInstance不是FactoryBean的实例，也不是Factory的引用，直接返回sharedInstance
- 从缓存中获取FactoryBean创建的Bean实例
- 如果换成中没有，那么使用FactoryBean的getObject方法获取Bean，如果需要postProcess，调用BeanPostProcessor处理bean
第一步一般都是在bean已经创建过的情况下，也不算是完整的bean创建过程
- 在缓存中没有获取的bean的情况下，也就是首次创建bean的时候，判断beanFactory是否有父级beanFactory如果有的话，交给父亲beanFactory完成。
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
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);
}
}
- bean的创建过程开始，根据之前解析的bean的依赖，首先创建当前bean实例依赖的bean
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
// 保证当前创建bean依赖的bean都已经创建了
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dependsOnBean : dependsOn) {
if (isDependent(beanName, dependsOnBean)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
}
registerDependentBean(dependsOnBean, beanName);
getBean(dependsOnBean);
}
}
- 创建bean实例，根据bean的scope执行不同的创建方式。singleton，prototype，其他的scope
4.1 我们看单例的bean创建方式。其内部调用的是createBean方法。createBean比较重要，放在下次再说
if (mbd.isSingleton()) {
// 获取单例，getSingleton方法内部掉的是回调中的getObject方法
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
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);
}
4.2 scope为prototype类型的bean创建方式，其在调用createBean前后调用了beforePrototypeCreation与afterPrototypeCreation方法，也和singleton类似了。
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);
}
4.3 不同的socpe创建的bean。只需要实现Scope接口即可。实现scope的get方法，其内部也是使用传入的匿名工厂类getObject
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, 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);
}
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);
}
}
- 判断是否需要将bean转换为我们指定类型的class。
// 调用函数时传递进来的requiredType，bean，并且bean的class类型能转换为requiredType。然后调用TypeConverter进行转换。
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
catch (TypeMismatchException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to convert bean '" + name + "' to required type [" +
ClassUtils.getQualifiedName(requiredType) + "]", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
- 返回bean。
最后
这次我们知道了bean的创建过程其实是在调用getBean的时候创建的。配置的scope也是在这时生效的。
