Spring5源码解析三
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Spring5源码解析（bean实例化）
在上一边的博客里面已经介绍：spring在bean扫描过程，已经将所有的bean保存在一个beanDefinitionMap的map对象中，但是这些bean还是一个beanDefinition，还没进行实例化的，所以这次就重点解析bean的实例化过程。 bean扫描过程源码分析：blog.csdn.net/qq_24101357…
- finishBeanFactoryInitialization(beanFactory);
- 合并父类，RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); 举个例子说明一下，不怎么重要：
<bean id="parentBd" class="com.llsydn.merge.PcBd">
<property name="name" value="parent"></property>
</bean>
<bean id="childBd" parent="parentBd">
<property name="name" value="children"></property>
</bean>
public class PcBd {
private String name;
public void setName(String name) {
this.name = name;
}
public void test() {
System.out.println(this.name);
}
}
public class test{
public static void main(String[] args) {
AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext();
ac.register(Appconfig.class);
ac.refresh();
PcBd parentBd = (PcBd) ac.getBean("parentBd");
parentBd.test();
PcBd childBd = (PcBd) ac.getBean("childBd");
childBd.test();
}
}
// 输出：
parent
children
上面的代码，主要是实现bean实例化的准备过程，从beanDefinitionNames中拿到被扫描出来的所有beanName。 然后遍历beanDefinitionNames，一个一个的调用getBean()方法，实例化这些bean对象。
- getBean(beanName)
- isSingletonCurrentlyInCreation 以为还没有需要创建对象的时候。
spring自动装配的模型 不等于 自动装配的技术。
- no 会使用 bytype技术
- bean的默认自动装配模型 == no
public class OrderService{ IndexService indexService; } 这个indexService，直接忽略了装配 public class OrderService{ @Autowired IndexService indexService; } 这个indexService会先使用bytype技术自动装配，找不到再使用byname自动装配
- 下面进入到doGetBean()进行分析
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
/**
* 通过 name 获取 beanName。这里不使用 name 直接作为 beanName 有两个原因
* 1、name 可能会以 & 字符开头，表明调用者想获取 FactoryBean 本身，而非 FactoryBean
* 实现类所创建的 bean。在 BeanFactory 中，FactoryBean 的实现类和其他的 bean 存储
* 方式是一致的，即 <beanName, bean>，beanName 中是没有 & 这个字符的。所以我们需要
* 将 name 的首字符 & 移除，这样才能从缓存里取到 FactoryBean 实例。
* 2、还是别名的问题，转换需要
*/
final String beanName = transformedBeanName(name);
Object bean;
/**
* 这个方法在初始化的时候会调用，在getBean的时候也会调用
* 为什么需要这么做呢？
* 也就是说spring在初始化的时候先获取这个对象
* 判断这个对象是否被实例化好了(普通情况下绝对为空====有一种情况可能不为空lazy=true,第二次调用)
* 从spring的bean容器中获取一个bean，由于spring中bean容器是一个map（singletonObjects）
* 所以你可以理解getSingleton(beanName)等于beanMap.get(beanName)
* 由于方法会在spring环境初始化的时候（就是对象被创建的时候调用一次）调用一次
* 还会在getBean的时候调用一次
* 所以再调试的时候需要特别注意，不能直接断点在这里，
* 需要先进入到annotationConfigApplicationContext.getBean(IndexDao.class)
* 之后再来断点，这样就确保了我们是在获取这个bean的时候调用的
*
* 需要说明的是在初始化时候调用一般都是返回null
*
* 第一次调用：isSingletonCurrentlyInCreation以为还没到开始创建对象的时候
*/
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
// 这里的代码是对于日志的记录，方便我们以后阅读应该注释，不影响spring功能
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 + "'");
}
}
/**
* 如果 sharedInstance 是普通的单例 bean，下面的方法会直接返回。但如果
* sharedInstance 是 FactoryBean 类型的，则需调用 getObject 工厂方法获取真正的
* bean 实例。如果用户想获取 FactoryBean 本身，这里也不会做特别的处理，直接返回
* 即可。毕竟 FactoryBean 的实现类本身也是一种 bean，只不过具有一点特殊的功能而已。
*/
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
/**
* 原型，判断当前正在创建的bean是不是原型。
* 如果是原型不应该在初始化的时候创建
*/
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory. 父工厂
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else 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);
}
}
if (!typeCheckOnly) {
//添加到alreadyCreated set集合当中，表示他已经创建过一场
markBeanAsCreated(beanName);
}
try {
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// 创建单例的bean
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
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);
}
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);
}
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, () -> {
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);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
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());
}
}
return (T) bean;
}
- createBean(beanName, mbd, args); 分析
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isDebugEnabled()) {
logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
// 处理 lookup-method 和 replace-method 配置，Spring 将这两个配置统称为 override method
try {
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// 在 bean 初始化前应用后置处理，如果后置处理返回的 bean 不为空，则直接返回
// 这个类需要通过代码演示
// 这个主要的作用是，将bean的所有依赖去到，直接返回一个寡对象。实现InstantiationAwareBeanPostProcessor接口。
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
// 调用doCreateBean 创建bean
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
- Object beanInstance = doCreateBean(beanName, mbdToUse, args); 分析
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean. 包装类
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
/**
* 创建 bean 实例，并将实例包裹在 BeanWrapper 实现类对象中返回。
* createBeanInstance中包含三种创建 bean 实例的方式：
* 1. 通过工厂方法创建 bean 实例
* 2. 通过构造方法自动注入（autowire by constructor）的方式创建 bean 实例
* 3. 通过无参构造方法方法创建 bean 实例
*
* 若 bean 的配置信息中配置了 lookup-method 和 replace-method，则会使用 CGLIB
* 增强 bean 实例。关于lookup-method和replace-method后面再说。
*/
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//拿到包装类的原生对象
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
//非常重要
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
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, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
//设置属性，非常重要
populateBean(beanName, mbd, instanceWrapper);
//执行后置处理器，aop就是在这里完成的处理
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 " +
"'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;
}
doCreateBean()方法主要的作用： 1.先利用反射技术生成bean的实例对象。createBeanInstance(beanName, mbd, args) 2.对实例对象的属性，进行自动装配。populateBean(beanName, mbd, instanceWrapper); 3.执行后置处理器，进行bean增强。 initializeBean(beanName, exposedObject, mbd);
- createBeanInstance(beanName, mbd, args) 利用反射技术实例化对象
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
Class<?> beanClass = resolveBeanClass(mbd, beanName);
/**
* 检测一个类的访问权限spring默认情况下对于非public的类是允许访问的。
*/
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
}
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
/**
*
* 如果工厂方法不为空，则通过工厂方法构建 bean 对象
* 这种构建 bean 的方式可以自己写个demo去试试
* 源码就不做深入分析了，有兴趣的同学可以和我私下讨论
* 如果设置了factoryMethod，就使用FactoryMethod方法实例化对象。（举例子实现）
*/
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
/**
* 从spring的原始注释可以知道这个是一个Shortcut，什么意思呢？快捷方式
* 当多次构建同一个 bean 时，可以使用这个Shortcut，
* 也就是说不在需要次推断应该使用哪种方式构造bean
* 比如在多次构建同一个prototype类型的 bean 时，就可以走此处的shortcut
* 这里的 resolved 和 mbd.constructorArgumentsResolved 将会在 bean 第一次实例化的过程中被设置
*/
boolean resolved = false;
boolean autowireNecessary = false; //是否必须要自动装配
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
//如果已经解析了构造方法的参数，则必须要通过一个带参构造方法来实例
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
//通过构造方法自动装配的方式构造 bean 对象
return autowireConstructor(beanName, mbd, null, null);
}
else {
//通过默认的无参构造方法进行
return instantiateBean(beanName, mbd);
}
}
//1.当有无参构造方法，就默认使用该无参构造方法，实例化对象。
//因为spring不知道，你是使用有参构造方法实例化对象，还是使用无参构造方法实例化对象，所以就简单一点，使用无参构造方法实例化对象。
//2.当且仅当只有一个有参构造方法，就使用该有参构造方法，实例化对象。
//当你有多个有参构造方法的时候，spring也是不知道该用哪个构造方法实例化对象，所以就简单一点，使用无参构造方法实例化对象。
//由后置处理器决定返回哪些构造方法
//拿到bean的构造方法，然后使用该构造方法实例化对象。（要用哪个构造方法实例化对象，交给BeanPostProcessors处理）
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
//使用默认的无参构造方法进行初始化
return instantiateBean(beanName, mbd);
}
createBeanInstance主要的步骤有： 1.判断bean是否可以访问。 2.判断bean是否有factory-method方法，如果有就调用factory-method方法实例化对象 3.判断bean是否是第二次实例化，并是否存在快捷方式实例化对象。 4.判断bean的构造方法：
1.当bean有无参构造方法，就默认使用该无参构造方法，实例化对象 2.当bean只有一个有参构造方法，就使用该有参构造方法，实例化对象 3.当bean有多个有参构造方法，使用无参构造方法，实例化对象。(spring无法判断要用那个构造方法)
备注：spring是使用构造方法方式，实例化对象
- determineConstructorsFromBeanPostProcessors() 用哪个构造方法实例化对象，交给BeanPostProcessors处理
protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName)
throws BeansException {
if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
if (ctors != null) {
return ctors;
}
}
}
}
return null;
}
#AutowiredAnnotationBeanPostProcessor
//决定使用哪个候选的构造方法
@Override
@Nullable
public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, final String beanName)
throws BeanCreationException {
// Let's check for lookup methods here..
if (!this.lookupMethodsChecked.contains(beanName)) {
try {
ReflectionUtils.doWithMethods(beanClass, method -> {
Lookup lookup = method.getAnnotation(Lookup.class);
if (lookup != null) {
Assert.state(this.beanFactory != null, "No BeanFactory available");
LookupOverride override = new LookupOverride(method, lookup.value());
try {
RootBeanDefinition mbd = (RootBeanDefinition) this.beanFactory.getMergedBeanDefinition(beanName);
mbd.getMethodOverrides().addOverride(override);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(beanName,
"Cannot apply @Lookup to beans without corresponding bean definition");
}
}
});
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName, "Lookup method resolution failed", ex);
}
this.lookupMethodsChecked.add(beanName);
}
// 候选构造器
// Quick check on the concurrent map first, with minimal locking.
Constructor<?>[] candidateConstructors = this.candidateConstructorsCache.get(beanClass);
if (candidateConstructors == null) {
// Fully synchronized resolution now...
synchronized (this.candidateConstructorsCache) {
candidateConstructors = this.candidateConstructorsCache.get(beanClass);
if (candidateConstructors == null) {
// 拿到bean的所有构造方法
Constructor<?>[] rawCandidates;
try {
rawCandidates = beanClass.getDeclaredConstructors();
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Resolution of declared constructors on bean Class [" + beanClass.getName() +
"] from ClassLoader [" + beanClass.getClassLoader() + "] failed", ex);
}
List<Constructor<?>> candidates = new ArrayList<>(rawCandidates.length);
Constructor<?> requiredConstructor = null;
Constructor<?> defaultConstructor = null;
Constructor<?> primaryConstructor = BeanUtils.findPrimaryConstructor(beanClass);
int nonSyntheticConstructors = 0;
for (Constructor<?> candidate : rawCandidates) {
if (!candidate.isSynthetic()) {
//记录bean有多少个构造方法
nonSyntheticConstructors++;
}
else if (primaryConstructor != null) {
continue;
}
AnnotationAttributes ann = findAutowiredAnnotation(candidate);
if (ann == null) {
Class<?> userClass = ClassUtils.getUserClass(beanClass);
if (userClass != beanClass) {
try {
Constructor<?> superCtor =
userClass.getDeclaredConstructor(candidate.getParameterTypes());
ann = findAutowiredAnnotation(superCtor);
}
catch (NoSuchMethodException ex) {
// Simply proceed, no equivalent superclass constructor found...
}
}
}
if (ann != null) {
if (requiredConstructor != null) {
throw new BeanCreationException(beanName,
"Invalid autowire-marked constructor: " + candidate +
". Found constructor with 'required' Autowired annotation already: " +
requiredConstructor);
}
boolean required = determineRequiredStatus(ann);
if (required) {
if (!candidates.isEmpty()) {
throw new BeanCreationException(beanName,
"Invalid autowire-marked constructors: " + candidates +
". Found constructor with 'required' Autowired annotation: " +
candidate);
}
requiredConstructor = candidate;
}
candidates.add(candidate);
}
//如果构造方法的没有参数，就是默认的构造方法。就使用该默认构造方法实例化对象。
else if (candidate.getParameterCount() == 0) {
defaultConstructor = candidate;
}
}
if (!candidates.isEmpty()) {
// Add default constructor to list of optional constructors, as fallback.
if (requiredConstructor == null) {
if (defaultConstructor != null) {
candidates.add(defaultConstructor);
}
else if (candidates.size() == 1 && logger.isWarnEnabled()) {
logger.warn("Inconsistent constructor declaration on bean with name '" + beanName +
"': single autowire-marked constructor flagged as optional - " +
"this constructor is effectively required since there is no " +
"default constructor to fall back to: " + candidates.get(0));
}
}
candidateConstructors = candidates.toArray(new Constructor<?>[0]);
}
else if (rawCandidates.length == 1 && rawCandidates[0].getParameterCount() > 0) {
//只有一个有参构造方法，返回该有参构造方法
candidateConstructors = new Constructor<?>[] {rawCandidates[0]};
}
else if (nonSyntheticConstructors == 2 && primaryConstructor != null &&
defaultConstructor != null && !primaryConstructor.equals(defaultConstructor)) {
candidateConstructors = new Constructor<?>[] {primaryConstructor, defaultConstructor};
}
else if (nonSyntheticConstructors == 1 && primaryConstructor != null) {
candidateConstructors = new Constructor<?>[] {primaryConstructor};
}
else {
//返null，即使用默认无参构造方法实例化对象。
candidateConstructors = new Constructor<?>[0];
}
this.candidateConstructorsCache.put(beanClass, candidateConstructors);
}
}
}
return (candidateConstructors.length > 0 ? candidateConstructors : null);
}