Spring版本
5.2.5.RELEASE
参考
源码解读
在《Spring源码解析（八）-创建单例bean》
的doCreateBean方法中，第一步是调用了createBeanInstance方法来创建一个bean实例
1. AbstractAutowireCapableBeanFactory#createBeanInstance
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
// 确保到了这一步beanClass已经被解析
Class<?> beanClass = resolveBeanClass(mbd, beanName);
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());
}
// 存在Supplier回调方法，则使用Supplier回调方法进行创建
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
// 通过factory method方法进行实例化
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
// 判断bean是否解析过
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
// 如果解析过，使用缓存，避免下面选择构造方法的性能开销
if (resolved) {
// 如果需要自动注入，采用自动注入的构造方法
if (autowireNecessary) {
return autowireConstructor(beanName, mbd, null, null);
}
else {
// 否则，使用默认实例bean方法
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
// 通过参数个数、类型等，确定最合适的构造方法
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
// 没有参数的情况下，获取偏爱的构造方法（该方法内部实现返回null）
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
// 使用无参构造方法作为兜底
return instantiateBean(beanName, mbd);
}
1、调用resolveBeanClass方法再次确保beanClass属性已经被解析，关于resolveBeanClass方法可以查看《Spring源码解析（八）-创建单例bean》
2、如果设置了Supplier回调方法，则使用Supplier回调方法进行创建
3、如果是静态工厂方法，通过FactoryBean的factory method方法进行实例化
4、抉择合适的构造方法，进行实例化
2.AbstractAutowireCapableBeanFactory#obtainFromSupplier
protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String beanName) {
Object instance;
// 使用临时变量保存currentlyCreatedBean当前值
String outerBean = this.currentlyCreatedBean.get();
// 将beanName设置到currentlyCreatedBean中，表示这是当前正在创建到bean
// currentlyCreatedBean.get()在getObjectForBeanInstance中会被调用（通过对currentlyCreatedBean使用find Usages发现）
this.currentlyCreatedBean.set(beanName);
try {
// 返回一个bean实例
instance = instanceSupplier.get();
}
finally {
// 还原原来的临时变量
if (outerBean != null) {
this.currentlyCreatedBean.set(outerBean);
}
else {
this.currentlyCreatedBean.remove();
}
}
if (instance == null) {
instance = new NullBean();
}
// 构造一个bean包装器，BeanWrapperImpl内初始化了几个参数，无其他逻辑
BeanWrapper bw = new BeanWrapperImpl(instance);
initBeanWrapper(bw);
return bw;
}
核心点在于instanceSupplier.get()调用相应的回调方法进行返回一个bean实例，之后构造一个BeanWrapper对象，然后进行初始化，并返回该对象
3. AbstractAutowireCapableBeanFactory#instantiateUsingFactoryMethod
Demo：
<bean id="dataformat1" class="java.text.DateFormat" factory-method="getDateInstance">
<constructor-arg value="2"></constructor-arg>
</bean>
<bean id="dataformat2" class="java.text.DateFormat" factory-method="getDateTimeInstance">
<constructor-arg index="0" value="2"></constructor-arg>
<constructor-arg index="1" value="2"></constructor-arg>
</bean>
源码：
protected BeanWrapper instantiateUsingFactoryMethod(
String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
return new ConstructorResolver(this).instantiateUsingFactoryMethod(beanName, mbd, explicitArgs);
}
3.1 ConstructorResolver#instantiateUsingFactoryMethod
public BeanWrapper instantiateUsingFactoryMethod(
String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
// 构造包装器对象
BeanWrapperImpl bw = new BeanWrapperImpl();
// 初始化
this.beanFactory.initBeanWrapper(bw);
Object factoryBean;
Class<?> factoryClass;
boolean isStatic;
String factoryBeanName = mbd.getFactoryBeanName();
if (factoryBeanName != null) {
// factoryBeanName和beanName相同的情况下，感觉就是一个蛋生鸡鸡生蛋的问题，所以要抛出异常进行拦截
// 另外，如果实例化的是FactoryBean本身，name是以&开头，也不会命中这一层判断
if (factoryBeanName.equals(beanName)) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"factory-bean reference points back to the same bean definition");
}
factoryBean = this.beanFactory.getBean(factoryBeanName);
// 判断该bean实例是否已经创建
// containsSingleton方法是判断singletonObjects是否包含该beanName
if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {
throw new ImplicitlyAppearedSingletonException();
}
factoryClass = factoryBean.getClass();
isStatic = false;
}
else {
// 静态工厂方法，此时需要提供BeanClass
// It's a static factory method on the bean class.
if (!mbd.hasBeanClass()) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"bean definition declares neither a bean class nor a factory-bean reference");
}
factoryBean = null;
factoryClass = mbd.getBeanClass();
isStatic = true;
}
Method factoryMethodToUse = null;
ArgumentsHolder argsHolderToUse = null;
Object[] argsToUse = null;
// 如果指定了参数，直接使用指定参数
if (explicitArgs != null) {
argsToUse = explicitArgs;
}
else {
// 否则，尝试从缓存中获取
Object[] argsToResolve = null;
synchronized (mbd.constructorArgumentLock) {
factoryMethodToUse = (Method) mbd.resolvedConstructorOrFactoryMethod;
if (factoryMethodToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached factory method...
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
if (argsToResolve != null) {
// 解析保存在mbd中的参数
argsToUse = resolvePreparedArguments(beanName, mbd, bw, factoryMethodToUse, argsToResolve, true);
}
}
if (factoryMethodToUse == null || argsToUse == null) {
// Need to determine the factory method...
// Try all methods with this name to see if they match the given arguments.
factoryClass = ClassUtils.getUserClass(factoryClass);
List<Method> candidates = null;
if (mbd.isFactoryMethodUnique) {
if (factoryMethodToUse == null) {
factoryMethodToUse = mbd.getResolvedFactoryMethod();
}
if (factoryMethodToUse != null) {
candidates = Collections.singletonList(factoryMethodToUse);
}
}
if (candidates == null) {
candidates = new ArrayList<>();
Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
for (Method candidate : rawCandidates) {
// 如果方法被static关键字修饰，并且是factoryMethod，那么加入候选方法中
if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {
candidates.add(candidate);
}
}
}
// 如果候选方法只有一个，并且没有要求参数，且有无参构造方法，那么，满足创建bean的要求，进行实例化
if (candidates.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {
Method uniqueCandidate = candidates.get(0);
// 如果唯一的候选方法参数个数为=0，满足mbd的无参构造方法
if (uniqueCandidate.getParameterCount() == 0) {
mbd.factoryMethodToIntrospect = uniqueCandidate;
synchronized (mbd.constructorArgumentLock) {
mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;
mbd.constructorArgumentsResolved = true;
mbd.resolvedConstructorArguments = EMPTY_ARGS;
}
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, uniqueCandidate, EMPTY_ARGS));
return bw;
}
}
// 多于1个，进行排序，排序规则：public且参数多的优先
if (candidates.size() > 1) { // explicitly skip immutable singletonList
candidates.sort(AutowireUtils.EXECUTABLE_COMPARATOR);
}
ConstructorArgumentValues resolvedValues = null;
boolean autowiring = (mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR);
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Method> ambiguousFactoryMethods = null;
// 实例化bean所需要的最少参数个数
int minNrOfArgs;
if (explicitArgs != null) {
minNrOfArgs = explicitArgs.length;
}
else {
// We don't have arguments passed in programmatically, so we need to resolve the
// arguments specified in the constructor arguments held in the bean definition.
if (mbd.hasConstructorArgumentValues()) {
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
resolvedValues = new ConstructorArgumentValues();
// 将mbd的构造参数解析进resolvedValues，比如解析下面的constructor-arg标签:
// <bean id="dataformat1" class="java.text.DateFormat" factory-method="getDateInstance">
// <constructor-arg value="2"></constructor-arg>
// </bean>
// 或者
// <bean id="dataformat2" class="java.text.DateFormat" factory-method="getDateTimeInstance">
// <constructor-arg index="0" value="2"></constructor-arg>
// <constructor-arg index="1" value="2"></constructor-arg>
// </bean>
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
else {
minNrOfArgs = 0;
}
}
LinkedList<UnsatisfiedDependencyException> causes = null;
for (Method candidate : candidates) {
int parameterCount = candidate.getParameterCount();
// 候选方法参数个数必须大于等于最小参数个数
if (parameterCount >= minNrOfArgs) {
ArgumentsHolder argsHolder;
Class<?>[] paramTypes = candidate.getParameterTypes();
if (explicitArgs != null) {
// Explicit arguments given -> arguments length must match exactly.
// 入参explicitArgs指定的情况下，这时候参数个数要求与入参explicitArgs的个数一致
if (paramTypes.length != explicitArgs.length) {
continue;
}
argsHolder = new ArgumentsHolder(explicitArgs);
}
else {
// Resolved constructor arguments: type conversion and/or autowiring necessary.
try {
// 获取候选方法的参数名称
String[] paramNames = null;
ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();
if (pnd != null) {
paramNames = pnd.getParameterNames(candidate);
}
argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw,
paramTypes, paramNames, candidate, autowiring, candidates.size() == 1);
}
catch (UnsatisfiedDependencyException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Ignoring factory method [" + candidate + "] of bean '" + beanName + "': " + ex);
}
// Swallow and try next overloaded factory method.
if (causes == null) {
causes = new LinkedList<>();
}
causes.add(ex);
continue;
}
}
// 对比先前查找出的候选值，寻找出最合适的一个
// Lenient : 宽容
//
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// Choose this factory method if it represents the closest match.
if (typeDiffWeight < minTypeDiffWeight) {
factoryMethodToUse = candidate;
argsHolderToUse = argsHolder;
argsToUse = argsHolder.arguments;
minTypeDiffWeight = typeDiffWeight;
ambiguousFactoryMethods = null;
}
// Find out about ambiguity: In case of the same type difference weight
// for methods with the same number of parameters, collect such candidates
// and eventually raise an ambiguity exception.
// However, only perform that check in non-lenient constructor resolution mode,
// and explicitly ignore overridden methods (with the same parameter signature).
// 如果存在多个相同值的候选方法，写入ambiguousFactoryMethods中，在后面会判断该集合，并抛出异常
else if (factoryMethodToUse != null && typeDiffWeight == minTypeDiffWeight &&
!mbd.isLenientConstructorResolution() &&
paramTypes.length == factoryMethodToUse.getParameterCount() &&
!Arrays.equals(paramTypes, factoryMethodToUse.getParameterTypes())) {
if (ambiguousFactoryMethods == null) {
ambiguousFactoryMethods = new LinkedHashSet<>();
ambiguousFactoryMethods.add(factoryMethodToUse);
}
ambiguousFactoryMethods.add(candidate);
}
}
}
// 经过上面的步骤，依旧没能决定出合适的factoryMethodToUse或者argsToUse，那么根据情况抛出各种异常
if (factoryMethodToUse == null || argsToUse == null) {
if (causes != null) {
UnsatisfiedDependencyException ex = causes.removeLast();
for (Exception cause : causes) {
this.beanFactory.onSuppressedException(cause);
}
throw ex;
}
List<String> argTypes = new ArrayList<>(minNrOfArgs);
if (explicitArgs != null) {
for (Object arg : explicitArgs) {
argTypes.add(arg != null ? arg.getClass().getSimpleName() : "null");
}
}
else if (resolvedValues != null) {
Set<ValueHolder> valueHolders = new LinkedHashSet<>(resolvedValues.getArgumentCount());
valueHolders.addAll(resolvedValues.getIndexedArgumentValues().values());
valueHolders.addAll(resolvedValues.getGenericArgumentValues());
for (ValueHolder value : valueHolders) {
String argType = (value.getType() != null ? ClassUtils.getShortName(value.getType()) :
(value.getValue() != null ? value.getValue().getClass().getSimpleName() : "null"));
argTypes.add(argType);
}
}
String argDesc = StringUtils.collectionToCommaDelimitedString(argTypes);
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"No matching factory method found: " +
(mbd.getFactoryBeanName() != null ?
"factory bean '" + mbd.getFactoryBeanName() + "'; " : "") +
"factory method '" + mbd.getFactoryMethodName() + "(" + argDesc + ")'. " +
"Check that a method with the specified name " +
(minNrOfArgs > 0 ? "and arguments " : "") +
"exists and that it is " +
(isStatic ? "static" : "non-static") + ".");
}
else if (void.class == factoryMethodToUse.getReturnType()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Invalid factory method '" + mbd.getFactoryMethodName() +
"': needs to have a non-void return type!");
}
else if (ambiguousFactoryMethods != null) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Ambiguous factory method matches found in bean '" + beanName + "' " +
"(hint: specify index/type/name arguments for simple parameters to avoid type ambiguities): " +
ambiguousFactoryMethods);
}
if (explicitArgs == null && argsHolderToUse != null) {
mbd.factoryMethodToIntrospect = factoryMethodToUse;
argsHolderToUse.storeCache(mbd, factoryMethodToUse);
}
}
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, factoryMethodToUse, argsToUse));
return bw;
}
方法很长，但整个过程不外乎就是做四件事：
- 找到需要进行实例化的
factoryBean - 找到负责实例化的方法
factoryMethodToUse - 找到负责实例化的方法所需要的参数
argsToUse - 使用上述三者，进行实例化
围绕上述三点，拆成多个部分来看源码
3.1.1 确定factoryBean
如果factoryBeanName不为空，那根据factoryBeanName找到factoryBean，以factoryBean的class类型作为factoryClass，否则，意味着使用的是静态方法，此时使用mbd定义的beanClass，也就是spring.xml文件中bean声明的class属性
Object factoryBean;
Class<?> factoryClass;
boolean isStatic;
String factoryBeanName = mbd.getFactoryBeanName();
if (factoryBeanName != null) {
// factoryBeanName和beanName相同的情况下，感觉就是一个蛋生鸡鸡生蛋的问题，所以要抛出异常进行拦截
// 另外，如果实例化的是FactoryBean本身，name是以&开头，也不会命中这一层判断
if (factoryBeanName.equals(beanName)) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"factory-bean reference points back to the same bean definition");
}
factoryBean = this.beanFactory.getBean(factoryBeanName);
// 判断该bean实例是否已经创建
// containsSingleton方法是判断singletonObjects是否包含该beanName
if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {
throw new ImplicitlyAppearedSingletonException();
}
factoryClass = factoryBean.getClass();
isStatic = false;
}
else {
// 静态工厂方法，此时需要提供BeanClass
// It's a static factory method on the bean class.
if (!mbd.hasBeanClass()) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"bean definition declares neither a bean class nor a factory-bean reference");
}
factoryBean = null;
factoryClass = mbd.getBeanClass();
isStatic = true;
}
3.1.2 确定实例化方法factoryMethodToUse及其构造参数argsToUse
如果instantiateUsingFactoryMethod方法入参指定了参数explicitArgs，那么直接使用explicitArgs作为argsToUse，否则，尝试从mbd中获取
// 如果指定了参数，直接使用指定参数
if (explicitArgs != null) {
argsToUse = explicitArgs;
}
else {
// 否则，尝试从mdb中获取（加入mbd已经解析出构造参数）
Object[] argsToResolve = null;
synchronized (mbd.constructorArgumentLock) {
factoryMethodToUse = (Method) mbd.resolvedConstructorOrFactoryMethod;
if (factoryMethodToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached factory method...
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
if (argsToResolve != null) {
// 如果此时argsToResolve不为空，说明argsToResolve已经被赋值为mbd.preparedConstructorArguments，此时使用mbd.preparedConstructorArguments进行解析
argsToUse = resolvePreparedArguments(beanName, mbd, bw, factoryMethodToUse, argsToResolve, true);
}
}
如果factoryMethodToUse和argsToUse都未能解析成功，则挑选出合适的候选方法集合candidates：
factoryClass = ClassUtils.getUserClass(factoryClass);
List<Method> candidates = null;
if (mbd.isFactoryMethodUnique) {
if (factoryMethodToUse == null) {
factoryMethodToUse = mbd.getResolvedFactoryMethod();
}
if (factoryMethodToUse != null) {
candidates = Collections.singletonList(factoryMethodToUse);
}
}
if (candidates == null) {
candidates = new ArrayList<>();
Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
for (Method candidate : rawCandidates) {
// 如果方法被static关键字修饰，并且是factoryMethod，那么加入候选方法中
if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {
candidates.add(candidate);
}
}
}
如果candidates只有一个，并且没有要求参数，且有无参方法，那么，满足创建bean的要求，进行实例化
// 如果候选方法只有一个，并且没有要求参数，且有无参方法，那么，满足创建bean的要求，进行实例化
if (candidates.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {
Method uniqueCandidate = candidates.get(0);
// 如果唯一的候选方法参数个数为=0，满足mbd的无参方法
if (uniqueCandidate.getParameterCount() == 0) {
mbd.factoryMethodToIntrospect = uniqueCandidate;
synchronized (mbd.constructorArgumentLock) {
mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;
mbd.constructorArgumentsResolved = true;
mbd.resolvedConstructorArguments = EMPTY_ARGS;
}
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, uniqueCandidate, EMPTY_ARGS));
return bw;
}
}
若是有多个，进行排序：
// 多于1个，进行排序，排序规则：public且参数多的优先
if (candidates.size() > 1) { // explicitly skip immutable singletonList
candidates.sort(AutowireUtils.EXECUTABLE_COMPARATOR);
}
解析进行实例化的时候需要的最少参数个数minNrOfArgs：
// 实例化bean所需要的最少参数个数
int minNrOfArgs;
if (explicitArgs != null) {
minNrOfArgs = explicitArgs.length;
}
else {
// We don't have arguments passed in programmatically, so we need to resolve the
// arguments specified in the constructor arguments held in the bean definition.
if (mbd.hasConstructorArgumentValues()) {
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
resolvedValues = new ConstructorArgumentValues();
// 将mbd的构造参数解析进resolvedValues，比如解析下面的constructor-arg标签:
// <bean id="dataformat1" class="java.text.DateFormat" factory-method="getDateInstance">
// <constructor-arg value="2"></constructor-arg>
// </bean>
// 或者
// <bean id="dataformat2" class="java.text.DateFormat" factory-method="getDateTimeInstance">
// <constructor-arg index="0" value="2"></constructor-arg>
// <constructor-arg index="1" value="2"></constructor-arg>
// </bean>
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
else {
minNrOfArgs = 0;
}
}
遍历candidates，挑选出最合适的方法，得到argsToUse
for (Method candidate : candidates) {
int parameterCount = candidate.getParameterCount();
// 候选方法参数个数必须大于等于最小参数个数
if (parameterCount >= minNrOfArgs) {
ArgumentsHolder argsHolder;
Class<?>[] paramTypes = candidate.getParameterTypes();
if (explicitArgs != null) {
// Explicit arguments given -> arguments length must match exactly.
// 入参explicitArgs指定的情况下，这时候参数个数要求与入参explicitArgs的个数一致
if (paramTypes.length != explicitArgs.length) {
continue;
}
argsHolder = new ArgumentsHolder(explicitArgs);
}
else {
// Resolved constructor arguments: type conversion and/or autowiring necessary.
try {
// 获取候选方法的参数名称
String[] paramNames = null;
ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();
if (pnd != null) {
paramNames = pnd.getParameterNames(candidate);
}
argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw,
paramTypes, paramNames, candidate, autowiring, candidates.size() == 1);
}
catch (UnsatisfiedDependencyException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Ignoring factory method [" + candidate + "] of bean '" + beanName + "': " + ex);
}
// Swallow and try next overloaded factory method.
if (causes == null) {
causes = new LinkedList<>();
}
causes.add(ex);
continue;
}
}
// 对比先前查找出的候选值，寻找出最合适的一个
// Lenient : 宽容
//
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// Choose this factory method if it represents the closest match.
if (typeDiffWeight < minTypeDiffWeight) {
factoryMethodToUse = candidate;
argsHolderToUse = argsHolder;
argsToUse = argsHolder.arguments;
minTypeDiffWeight = typeDiffWeight;
ambiguousFactoryMethods = null;
}
// Find out about ambiguity: In case of the same type difference weight
// for methods with the same number of parameters, collect such candidates
// and eventually raise an ambiguity exception.
// However, only perform that check in non-lenient constructor resolution mode,
// and explicitly ignore overridden methods (with the same parameter signature).
// 如果存在多个相同值的候选方法，写入ambiguousFactoryMethods中，在后面会判断该集合，并抛出异常
else if (factoryMethodToUse != null && typeDiffWeight == minTypeDiffWeight &&
!mbd.isLenientConstructorResolution() &&
paramTypes.length == factoryMethodToUse.getParameterCount() &&
!Arrays.equals(paramTypes, factoryMethodToUse.getParameterTypes())) {
if (ambiguousFactoryMethods == null) {
ambiguousFactoryMethods = new LinkedHashSet<>();
ambiguousFactoryMethods.add(factoryMethodToUse);
}
ambiguousFactoryMethods.add(candidate);
}
}
}
如argsToUse和factoryMethodToUse依旧为空，那么抛出异常，此时实例化失败
// 经过上面的步骤，依旧没能决定出合适的factoryMethodToUse或者argsToUse，那么根据情况抛出各种异常
if (factoryMethodToUse == null || argsToUse == null) {
if (causes != null) {
UnsatisfiedDependencyException ex = causes.removeLast();
for (Exception cause : causes) {
this.beanFactory.onSuppressedException(cause);
}
throw ex;
}
List<String> argTypes = new ArrayList<>(minNrOfArgs);
if (explicitArgs != null) {
for (Object arg : explicitArgs) {
argTypes.add(arg != null ? arg.getClass().getSimpleName() : "null");
}
}
else if (resolvedValues != null) {
Set<ValueHolder> valueHolders = new LinkedHashSet<>(resolvedValues.getArgumentCount());
valueHolders.addAll(resolvedValues.getIndexedArgumentValues().values());
valueHolders.addAll(resolvedValues.getGenericArgumentValues());
for (ValueHolder value : valueHolders) {
String argType = (value.getType() != null ? ClassUtils.getShortName(value.getType()) :
(value.getValue() != null ? value.getValue().getClass().getSimpleName() : "null"));
argTypes.add(argType);
}
}
String argDesc = StringUtils.collectionToCommaDelimitedString(argTypes);
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"No matching factory method found: " +
(mbd.getFactoryBeanName() != null ?
"factory bean '" + mbd.getFactoryBeanName() + "'; " : "") +
"factory method '" + mbd.getFactoryMethodName() + "(" + argDesc + ")'. " +
"Check that a method with the specified name " +
(minNrOfArgs > 0 ? "and arguments " : "") +
"exists and that it is " +
(isStatic ? "static" : "non-static") + ".");
}
else if (void.class == factoryMethodToUse.getReturnType()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Invalid factory method '" + mbd.getFactoryMethodName() +
"': needs to have a non-void return type!");
}
else if (ambiguousFactoryMethods != null) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Ambiguous factory method matches found in bean '" + beanName + "' " +
"(hint: specify index/type/name arguments for simple parameters to avoid type ambiguities): " +
ambiguousFactoryMethods);
}
3.1.3 通过反射实例化
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, factoryMethodToUse, argsToUse));
private Object instantiate(String beanName, RootBeanDefinition mbd,
@Nullable Object factoryBean, Method factoryMethod, Object[] args) {
try {
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged((PrivilegedAction<Object>) () ->
this.beanFactory.getInstantiationStrategy().instantiate(
mbd, beanName, this.beanFactory, factoryBean, factoryMethod, args),
this.beanFactory.getAccessControlContext());
}
else {
// 通过反射调用对应方法进行实例化
return this.beanFactory.getInstantiationStrategy().instantiate(
mbd, beanName, this.beanFactory, factoryBean, factoryMethod, args);
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean instantiation via factory method failed", ex);
}
}
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
@Nullable Object factoryBean, final Method factoryMethod, Object... args) {
try {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
ReflectionUtils.makeAccessible(factoryMethod);
return null;
});
}
else {
ReflectionUtils.makeAccessible(factoryMethod);
}
Method priorInvokedFactoryMethod = currentlyInvokedFactoryMethod.get();
try {
currentlyInvokedFactoryMethod.set(factoryMethod);
Object result = factoryMethod.invoke(factoryBean, args);
if (result == null) {
result = new NullBean();
}
return result;
}
finally {
if (priorInvokedFactoryMethod != null) {
currentlyInvokedFactoryMethod.set(priorInvokedFactoryMethod);
}
else {
currentlyInvokedFactoryMethod.remove();
}
}
}
// 略
}
4. ConstructorResolver#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;
ArgumentsHolder argsHolderToUse = null;
Object[] argsToUse = null;
if (explicitArgs != null) {
argsToUse = explicitArgs;
}
else {
Object[] argsToResolve = null;
synchronized (mbd.constructorArgumentLock) {
constructorToUse = (Constructor<?>) mbd.resolvedConstructorOrFactoryMethod;
if (constructorToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached constructor...
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
// 如果此时argsToResolve不为空，说明argsToResolve已经被赋值为mbd.preparedConstructorArguments，此时使用mbd.preparedConstructorArguments进行解析
if (argsToResolve != null) {
argsToUse = resolvePreparedArguments(beanName, mbd, bw, constructorToUse, argsToResolve, true);
}
}
if (constructorToUse == null || argsToUse == null) {
// Take specified constructors, if any.
// 如果入参指定了候选构造参数，则使用
Constructor<?>[] candidates = chosenCtors;
if (candidates == null) {
Class<?> beanClass = mbd.getBeanClass();
try {
// 否则，获取候选构造参数
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);
}
}
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;
int minNrOfArgs;
if (explicitArgs != null) {
minNrOfArgs = explicitArgs.length;
}
else {
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
resolvedValues = new ConstructorArgumentValues();
// 将mbd的参数解析到resolvedValues中
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
AutowireUtils.sortConstructors(candidates);
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Constructor<?>> ambiguousConstructors = null;
LinkedList<UnsatisfiedDependencyException> causes = null;
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();
if (pnd != null) {
paramNames = pnd.getParameterNames(candidate);
}
}
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 LinkedList<>();
}
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);
}
}
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);
}
}
Assert.state(argsToUse != null, "Unresolved constructor arguments");
bw.setBeanInstance(instantiate(beanName, mbd, constructorToUse, argsToUse));
return bw;
}
该方法和第三点使用工厂方法实例化大部分代码是相似的，这里就无须多言了，主要看一下instantiate方法
4.1 ConstructorResolver#instantiate
private Object instantiate(
String beanName, RootBeanDefinition mbd, Constructor<?> constructorToUse, Object[] argsToUse) {
try {
// 获取实例化策略，默认是CglibSubclassingInstantiationStrategy
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 {
// 选择合适的策略进行实例化
return strategy.instantiate(mbd, beanName, this.beanFactory, constructorToUse, argsToUse);
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean instantiation via constructor failed", ex);
}
}
先获取实例化策略，再交由获取到的实例化策略去执行具体的实例化逻辑
4.2 SimpleInstantiationStrategy#instantiate
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
final Constructor<?> ctor, Object... args) {
// 如果没有replace-method、lookup-method，以及使用@Lookup注解，那么使用反射进行实例化
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;
});
}
// 使用cror构造方法通过反射实例化
return BeanUtils.instantiateClass(ctor, args);
}
else {
// 否则，创建cglib子类实例化
return instantiateWithMethodInjection(bd, beanName, owner, ctor, args);
}
}
如果使用了replace-method、lookup-method、或者使用了@Lookup注解，则创建cglib子类进行实例化，否则直接使用反射进行实例化
4.3 BeanUtils#instantiateClass
反射进行实例化，核心代码如下：
ReflectionUtils.makeAccessible(ctor);
if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {
return KotlinDelegate.instantiateClass(ctor, args);
}
else {
Class<?>[] parameterTypes = ctor.getParameterTypes();
Assert.isTrue(args.length <= parameterTypes.length, "Can't specify more arguments than constructor parameters");
Object[] argsWithDefaultValues = new Object[args.length];
for (int i = 0 ; i < args.length; i++) {
if (args[i] == null) {
// 如果参数为空，获取对应类型的默认值
Class<?> parameterType = parameterTypes[i];
argsWithDefaultValues[i] = (parameterType.isPrimitive() ? DEFAULT_TYPE_VALUES.get(parameterType) : null);
}
else {
argsWithDefaultValues[i] = args[i];
}
}
// 反射实例化对象
return ctor.newInstance(argsWithDefaultValues);
}
4.4 SimpleInstantiationStrategy#instantiateWithMethodInjection
创建cglib子类进行实例化
protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName,
BeanFactory owner, @Nullable Constructor<?> ctor, Object... args) {
throw new UnsupportedOperationException("Method Injection not supported in SimpleInstantiationStrategy");
}
该方法默认没有实现，交由子类CglibSubclassingInstantiationStrategy来实现：
@Override
protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
return instantiateWithMethodInjection(bd, beanName, owner, null);
}
@Override
protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
@Nullable Constructor<?> ctor, Object... args) {
// Must generate CGLIB subclass...
return new CglibSubclassCreator(bd, owner).instantiate(ctor, args);
}
instantiate方法具体实现：
public Object instantiate(@Nullable Constructor<?> ctor, Object... args) {
// 创建子类
Class<?> subclass = createEnhancedSubclass(this.beanDefinition);
Object instance;
if (ctor == null) {
// 如果构造器为空，则通过反射获取实例
instance = BeanUtils.instantiateClass(subclass);
}
else {
try {
// 获取子类构造方法
Constructor<?> enhancedSubclassConstructor = subclass.getConstructor(ctor.getParameterTypes());
// 进行实例化
instance = enhancedSubclassConstructor.newInstance(args);
}
catch (Exception ex) {
throw new BeanInstantiationException(this.beanDefinition.getBeanClass(),
"Failed to invoke constructor for CGLIB enhanced subclass [" + subclass.getName() + "]", ex);
}
}
// SPR-10785: set callbacks directly on the instance instead of in the
// enhanced class (via the Enhancer) in order to avoid memory leaks.
Factory factory = (Factory) instance;
factory.setCallbacks(new Callback[] {NoOp.INSTANCE,
new LookupOverrideMethodInterceptor(this.beanDefinition, this.owner),
new ReplaceOverrideMethodInterceptor(this.beanDefinition, this.owner)});
return instance;
}
5. ConstructorResolver#instantiateBean
protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
try {
Object beanInstance;
final BeanFactory parent = this;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
getInstantiationStrategy().instantiate(mbd, beanName, parent),
getAccessControlContext());
}
else {
// 使用合适的实例化策略，默认是cglib
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}
大部分逻辑在第四点基本覆盖了
总结
可以看到，在创建bean实例这块上，因为创建bean可以有多种方式：
- 通过
Supplier - 通过
factory method - 通过构造方法
- 通过默认构造方法
spring在这方面上花了很多精力，尤其是抉择合适的factory method和构造方法上，使用了大量代码来确定合适的方法和参数。
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