Spring源码-AbstractAutowireCapableBeanFactory的autowireConstructor
autowireConstructor：
protected BeanWrapper autowireConstructor(
String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] ctors, @Nullable Object[] explicitArgs) {
return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
}
ConstructorResolver的autowireConstructor：
public BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd,
@Nullable Constructor<?>[] chosenCtors, @Nullable Object[] explicitArgs) {
BeanWrapperImpl bw = new BeanWrapperImpl();
this.beanFactory.initBeanWrapper(bw);
Constructor<?> constructorToUse = null; // 使用的构造函数
ArgumentsHolder argsHolderToUse = null; // 使用的参数封装
Object[] argsToUse = null; // 构造参数
if (explicitArgs != null) {
argsToUse = explicitArgs;
}
else {
Object[] argsToResolve = null;
synchronized (mbd.constructorArgumentLock) {
constructorToUse = (Constructor<?>) mbd.resolvedConstructorOrFactoryMethod; // 获取BeanDefinition中解析完成的构造函数
if (constructorToUse != null && mbd.constructorArgumentsResolved) {
// 从缓存中找到了构造器，那么继续从缓存中寻找缓存的构造器参数
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
argsToResolve = mbd.preparedConstructorArguments; // 没有缓存的参数，就需要获取配置文件中配置的参数
}
}
}
// 如果缓存中没有缓存的参数的话，即argsToResolve不为空，就需要解析配置的参数
if (argsToResolve != null) {
// 解析参数类型，比如将配置的String类型转换为list、boolean等类型
argsToUse = resolvePreparedArguments(beanName, mbd, bw, constructorToUse, argsToResolve);
}
}
if (constructorToUse == null || argsToUse == null) {
// Take specified constructors, if any.
Constructor<?>[] candidates = chosenCtors;
if (candidates == null) {
// 如果candidates为null,则获取bean的Class对象，在获取所有的构造函数
Class<?> beanClass = mbd.getBeanClass();
try {
candidates = (mbd.isNonPublicAccessAllowed() ?
beanClass.getDeclaredConstructors() : beanClass.getConstructors());
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Resolution of declared constructors on bean Class [" + beanClass.getName() +
"] from ClassLoader [" + beanClass.getClassLoader() + "] failed", ex);
}
}
// 如果candidates只有一个元素 且 没有传入构造函数值 且 mbd也没有构造函数参数值则调用唯一的构造函数并放到缓存中。
if (candidates.length == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {
Constructor<?> uniqueCandidate = candidates[0];
if (uniqueCandidate.getParameterCount() == 0) {
synchronized (mbd.constructorArgumentLock) {
mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;
mbd.constructorArgumentsResolved = true;
mbd.resolvedConstructorArguments = EMPTY_ARGS;
}
bw.setBeanInstance(instantiate(beanName, mbd, uniqueCandidate, EMPTY_ARGS));
return bw;
}
}
// Need to resolve the constructor.
boolean autowiring = (chosenCtors != null ||
mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR);
ConstructorArgumentValues resolvedValues = null;
// 获取构造函数的最小参数个数
int minNrOfArgs;
if (explicitArgs != null) {
minNrOfArgs = explicitArgs.length;
}
else {
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
resolvedValues = new ConstructorArgumentValues();
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
// 对候选构造函数排序
AutowireUtils.sortConstructors(candidates);
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Constructor<?>> ambiguousConstructors = null;
Deque<UnsatisfiedDependencyException> causes = null;
// 以下的循环遍历所有的候选构造函数，通过参数个数，参数的类型计算构造函数的typeDiffWeight值，选取typeDiffWeight最小的最为最优构造函数
for (Constructor<?> candidate : candidates) {
int parameterCount = candidate.getParameterCount();
if (constructorToUse != null && argsToUse != null && argsToUse.length > parameterCount) {
// Already found greedy constructor that can be satisfied ->
// do not look any further, there are only less greedy constructors left.
break;
}
if (parameterCount < minNrOfArgs) {
continue;
}
ArgumentsHolder argsHolder;
Class<?>[] paramTypes = candidate.getParameterTypes();
if (resolvedValues != null) {
try {
String[] paramNames = ConstructorPropertiesChecker.evaluate(candidate, parameterCount);
if (paramNames == null) {
ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer(); // 获取参数名称探索器
if (pnd != null) {
paramNames = pnd.getParameterNames(candidate); // 获取指定构造函数的参数名称
}
}
// 根据名称和数据类型创建argsHolder
argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw, paramTypes, paramNames,
getUserDeclaredConstructor(candidate), autowiring, candidates.length == 1);
}
catch (UnsatisfiedDependencyException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Ignoring constructor [" + candidate + "] of bean '" + beanName + "': " + ex);
}
// Swallow and try next constructor.
if (causes == null) {
causes = new ArrayDeque<>(1);
}
causes.add(ex);
continue;
}
}
else {
// Explicit arguments given -> arguments length must match exactly.
if (parameterCount != explicitArgs.length) {
continue;
}
argsHolder = new ArgumentsHolder(explicitArgs);
}
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// Choose this constructor if it represents the closest match.
if (typeDiffWeight < minTypeDiffWeight) {
constructorToUse = candidate;
argsHolderToUse = argsHolder;
argsToUse = argsHolder.arguments;
minTypeDiffWeight = typeDiffWeight;
ambiguousConstructors = null;
}
else if (constructorToUse != null && typeDiffWeight == minTypeDiffWeight) {
if (ambiguousConstructors == null) {
ambiguousConstructors = new LinkedHashSet<>();
ambiguousConstructors.add(constructorToUse);
}
ambiguousConstructors.add(candidate);
}
}
//以下两种情况会抛异常
// 1、没有确定使用的构造函数
// 2、存在模糊的构造函数并且不允许存在模糊的构造函数
if (constructorToUse == null) {
if (causes != null) {
UnsatisfiedDependencyException ex = causes.removeLast();
for (Exception cause : causes) {
this.beanFactory.onSuppressedException(cause);
}
throw ex;
}
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Could not resolve matching constructor " +
"(hint: specify index/type/name arguments for simple parameters to avoid type ambiguities)");
}
else if (ambiguousConstructors != null && !mbd.isLenientConstructorResolution()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Ambiguous constructor matches found in bean '" + beanName + "' " +
"(hint: specify index/type/name arguments for simple parameters to avoid type ambiguities): " +
ambiguousConstructors);
}
if (explicitArgs == null && argsHolderToUse != null) {
argsHolderToUse.storeCache(mbd, constructorToUse); // 将解析的构造函数加入缓存
}
}
Assert.state(argsToUse != null, "Unresolved constructor arguments");
bw.setBeanInstance(instantiate(beanName, mbd, constructorToUse, argsToUse)); // 通过构造函数实例化bean并加入BeanWrapper中
return bw;
}
instantiate：
private Object instantiate(
String beanName, RootBeanDefinition mbd, Constructor<?> constructorToUse, Object[] argsToUse) {
try {
InstantiationStrategy strategy = this.beanFactory.getInstantiationStrategy();
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged((PrivilegedAction<Object>) () ->
strategy.instantiate(mbd, beanName, this.beanFactory, constructorToUse, argsToUse),
this.beanFactory.getAccessControlContext());
}
else {
return strategy.instantiate(mbd, beanName, this.beanFactory, constructorToUse, argsToUse);
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean instantiation via constructor failed", ex);
}
}
根据实例化策略实例化bean。
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
final Constructor<?> ctor, Object... args) {
if (!bd.hasMethodOverrides()) {
if (System.getSecurityManager() != null) {
// use own privileged to change accessibility (when security is on)
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
ReflectionUtils.makeAccessible(ctor);
return null;
});
}
return BeanUtils.instantiateClass(ctor, args);
}
else {
return instantiateWithMethodInjection(bd, beanName, owner, ctor, args);
}
}
如果没有MethodOverrides，即没有lookup-method和replaced-method标签，则调用构造函数反射实例化bean，否则生成cglib代理处理lookup-method和replaced-method标签
