什么场景会进行第二次构造推断
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
//1.第一次推断出来的构造不为空
//2.自动注入模式为构造注入
//这两种情况会进行第二次构造推断
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
ConstructorResolver#autowireConstructor
public BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd,
@Nullable Constructor<?>[] chosenCtors, @Nullable Object[] explicitArgs) {
BeanWrapperImpl bw = new BeanWrapperImpl();
this.beanFactory.initBeanWrapper(bw);
//需要被使用的 构造方法
Constructor<?> constructorToUse = null;
//构造方法的入参数组封装类
ArgumentsHolder argsHolderToUse = null;
//构造方法的入参数组
Object[] argsToUse = null;
// explicitArgs 都为空
if (explicitArgs != null) {
argsToUse = explicitArgs;
}
else {
Object[] argsToResolve = null;
synchronized (mbd.constructorArgumentLock) {
//判断 resolvedConstructorOrFactoryMethod 是否为空
//和 constructorArgumentsResolved是否为true
//这两个是什么意思,如果这个bd已经构造推断过这两个字段就会有值
//使用的场景主要是原型模式,如果是单例的话,这两个都是不符合的
constructorToUse = (Constructor<?>) mbd.resolvedConstructorOrFactoryMethod;
if (constructorToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached constructor...
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
//通过构造参数,找到构造参数的值
if (argsToResolve != null) {
argsToUse = resolvePreparedArguments(beanName, mbd, bw, constructorToUse, argsToResolve, true);
}
}
//如果 constructorToUse 等于null,说明构造还没被推断过,单例会到这里来
if (constructorToUse == null || argsToUse == null) {
// chosenCtors 是从后置处理器推断来的构造
Constructor<?>[] candidates = chosenCtors;
if (candidates == null) {
//如果第一次推断的构造为空,就会获取所有的构造方法
Class<?> beanClass = mbd.getBeanClass();
try {
candidates = (mbd.isNonPublicAccessAllowed() ?
beanClass.getDeclaredConstructors() : beanClass.getConstructors());
}
}
//如果推断的只有一个构造或者只有一个构造,自动装配模式是构造
//而且这个构造是无参构造,就通过无参构造反射出对象
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;
}
}
// chosenCtors != null 说明第一次推断的参数是有值的
//mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR
//自动注入模式为构造注入
boolean autowiring = (chosenCtors != null ||
mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR);
ConstructorArgumentValues resolvedValues = null;
//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);
}
//对构造进行排序,排序方式优先级,比如根据public,private,根据构造方法的入参进行排序
//一般public在前面,构造方法的入参个数多的在前面
AutowireUtils.sortConstructors(candidates);
//最小差异权重为 integer的最大值
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Constructor<?>> ambiguousConstructors = null;
LinkedList<UnsatisfiedDependencyException> causes = null;
//对候选的构造方法进行循环
for (Constructor<?> candidate : candidates) {
//获取构造方法的参数集合
Class<?>[] paramTypes = candidate.getParameterTypes();
//如果可以用的构造和参数不为空,而且之前的构造的入参个数大于现在的入参个数,就是用之前的
if (constructorToUse != null && argsToUse != null && argsToUse.length > paramTypes.length) {
// Already found greedy constructor that can be satisfied ->
// do not look any further, there are only less greedy constructors left.
break;
}
//如果参数个数小于最小参数个数 minNrOfArgs 默认为零,所以一般不满足
if (paramTypes.length < minNrOfArgs) {
continue;
}
ArgumentsHolder argsHolder;
//resolvedValues 不为空,在上面已经new出来了
//根据入参找出入参值,如果有入参在spring容器中找不到就continue出来
if (resolvedValues != null) {
try {
String[] paramNames = ConstructorPropertiesChecker.evaluate(candidate, paramTypes.length);
if (paramNames == null) {
ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();
if (pnd != null) {
paramNames = pnd.getParameterNames(candidate);
}
}
argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw, paramTypes, paramNames,
getUserDeclaredConstructor(candidate), autowiring, candidates.length == 1);
}
}
//这个不会进去
else {
// Explicit arguments given -> arguments length must match exactly.
if (paramTypes.length != explicitArgs.length) {
continue;
}
argsHolder = new ArgumentsHolder(explicitArgs);
}
//获取该构造方法的类型差异权重
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// 如果该类型差异权重比最小差异权重还小,说明满足,就设置到要被使用的构造字段里面
if (typeDiffWeight < minTypeDiffWeight) {
constructorToUse = candidate;
argsHolderToUse = argsHolder;
argsToUse = argsHolder.arguments;
minTypeDiffWeight = typeDiffWeight;
ambiguousConstructors = null;
}
//如果没有需要被使用的构造,而且最小差异权重跟当前差异权重一样
//就把当前的构造放到 ambiguousConstructors 里面
else if (constructorToUse != null && typeDiffWeight == minTypeDiffWeight) {
if (ambiguousConstructors == null) {
ambiguousConstructors = new LinkedHashSet<>();
ambiguousConstructors.add(constructorToUse);
}
ambiguousConstructors.add(candidate);
}
}
//如果最后构造为空,就抛出异常
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)");
}
//ambiguousConstructors 存放差异权重相同的的构造
//如果存在差异权重相同的构造,而且 isLenientConstructorResolution = false 就会抛出异常
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) {
//将推断出来的构造放到bd,方便原型模式的实例化
argsHolderToUse.storeCache(mbd, constructorToUse);
}
}
//通过构造反射出对象
Assert.state(argsToUse != null, "Unresolved constructor arguments");
bw.setBeanInstance(instantiate(beanName, mbd, constructorToUse, argsToUse));
return bw;
}
流程图: