上一节我们分析到了createBean，而真正创建Bean的过程在doCreateBean过程，我们可以发现Spring的编码风格，do才是真正的过程，不带do的通常是在做在准备过程，并且我们跳过了一些地方，比如说后置处理器，后面会有详细的章节来解析后置处理器，但是并不妨碍正常分析创建Bean的这个过程。
doCreateBean(一)
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// BeanWrapper实例的包装类.
BeanWrapper instanceWrapper = null;
//如果mbd是单例 尝试从factoryBeanCache中获取中获取
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//开始实例化
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
...
}
createBeanInstance(一)
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
//保证这个时候bean class 已经被处理过
Class<?> beanClass = resolveBeanClass(mbd, beanName);
//如果beanClass不为null 并且修饰符不为public 而且 不允许修饰符为其他的情况下抛出异常
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());
}
//java1.8 Supplier有点类似于对象工厂
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
//如果Supplier不为null 则直接调用Supplier的get方法获得实例并返回
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
//尝试从FactoryMethod获取实例
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
...
}
instantiateUsingFactoryMethod
public BeanWrapper instantiateUsingFactoryMethod(
String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
//创建一个实例包装实现类对象
BeanWrapperImpl bw = new BeanWrapperImpl();
//设置ConversionService 和 CustomEditor
this.beanFactory.initBeanWrapper(bw);
Object factoryBean;
Class<?> factoryClass;
boolean isStatic;
String factoryBeanName = mbd.getFactoryBeanName();
if (factoryBeanName != null) {
//如果factoryBeanName 和 beanName 相等 报异常
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);
//即将创建的单例bean隐式出现
if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {
throw new ImplicitlyAppearedSingletonException();
}
factoryClass = factoryBean.getClass();
isStatic = false;
}
else {
//factoryBeanName为null 那么说明是bean中的静态工厂方法
// 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");
}
//不存在factoryBean 则 为null
factoryBean = null;
factoryClass = mbd.getBeanClass();
isStatic = true;
}
Method factoryMethodToUse = null;
ArgumentsHolder argsHolderToUse = null;
Object[] argsToUse = null;
//如果有显式的参数则直接用
if (explicitArgs != null) {
argsToUse = explicitArgs;
}
else {
Object[] argsToResolve = null;
synchronized (mbd.constructorArgumentLock) {
factoryMethodToUse = (Method) mbd.resolvedConstructorOrFactoryMethod;
if (factoryMethodToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached factory method...
//尝试从resolvedConstructorArguments 获取已处理的参数
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
//获取未处理的参数等待下一步处理
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
//处理未处理的参数(后面会有章节解析)
if (argsToResolve != null) {
argsToUse = resolvePreparedArguments(beanName, mbd, bw, factoryMethodToUse, argsToResolve, true);
}
}
//如果factoryMethodToUse为null或者argsToUse
//则需要确定出工厂方法
//尝试通过name来查找所有的方法是否匹配给定的参数
if (factoryMethodToUse == null || argsToUse == null) {
factoryClass = ClassUtils.getUserClass(factoryClass);
List<Method> candidateList = null;
//如果factoryMethod唯一
if (mbd.isFactoryMethodUnique) {
if (factoryMethodToUse == null) {
//尝试获取已处理的factoryMethod
factoryMethodToUse = mbd.getResolvedFactoryMethod();
}
if (factoryMethodToUse != null) {
//这个方法主要用于只有一个元素的优化，减少内存分配，无需分配额外的内存
candidateList = Collections.singletonList(factoryMethodToUse);
}
}
if (candidateList == null) {
candidateList = new ArrayList<>();
//通过反射获取所有DeclaredMethods
Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
for (Method candidate : rawCandidates) {
//修饰符是static 且 是工厂方法就加进集合
if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {
candidateList.add(candidate);
}
}
}
//如果大小为1 而且 没有显式参数 而且mbd表明为无参构造函数
//这时候就可以确定这个就是工厂方法
if (candidateList.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {
Method uniqueCandidate = candidateList.get(0);
if (uniqueCandidate.getParameterCount() == 0) {
//内省factoryMethod
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;
}
}
Method[] candidates = candidateList.toArray(new Method[0]);
//根据修饰符对Method进行排序
//public的排在前面，参数多的排在前面
AutowireUtils.sortFactoryMethods(candidates);
ConstructorArgumentValues resolvedValues = null;
//AUTOWIRE_CONSTRUCTOR 构造器注入
boolean autowiring = (mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR);
//定义一个最小Type权重
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Method> ambiguousFactoryMethods = null;
//定义方法需要的最小参数个数
int minNrOfArgs;
//如果显式参数不为null 最小参数个数就等于显式参数的长度
if (explicitArgs != null) {
minNrOfArgs = explicitArgs.length;
}
else {
//我们没有以编程方式(硬编码)把参数代入，所以我们需要解析
//beanDefinition中特定的构造器参数
if (mbd.hasConstructorArgumentValues()) {
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
resolvedValues = new ConstructorArgumentValues();
//主要解析Array，Set，Map，props和字符串类型的间接引用(后面的章节会分析)
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
else {
minNrOfArgs = 0;
}
}
LinkedList<UnsatisfiedDependencyException> causes = null;
for (Method candidate : candidates) {
Class<?>[] paramTypes = candidate.getParameterTypes();
//method中的paramTypes大于或者等于最小参数个数
if (paramTypes.length >= minNrOfArgs) {
ArgumentsHolder argsHolder;
if (explicitArgs != null) {
// 如果显式参数不为null 那么paramTypes长度不等于显式参数则跳过.
if (paramTypes.length != explicitArgs.length) {
continue;
}
argsHolder = new ArgumentsHolder(explicitArgs);
}
else {
// Resolved constructor arguments: type conversion and/or autowiring necessary.
try {
String[] paramNames = null;
ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();
if (pnd != null) {
paramNames = pnd.getParameterNames(candidate);
}
//这里我们只关注这个方法是为了创建参数数组
//具体怎么创建 后面章节会分析
argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw,
paramTypes, paramNames, candidate, autowiring, candidates.length == 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;
}
}
//isLenientConstructorResolution()判断策略是否宽松
//宽松策略下，使用spring构造的参数数组的类型和获取到的构造方法的参数类型进行对比。
//严格策略下，还需要检查能否将构造方法的参数复制到对应的属性中
//会返回一个数值，作为构造方法和参数的差异值
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// 根据最小权重找到最匹配的factory method
if (typeDiffWeight < minTypeDiffWeight) {
factoryMethodToUse = candidate;
argsHolderToUse = argsHolder;
argsToUse = argsHolder.arguments;
minTypeDiffWeight = typeDiffWeight;
ambiguousFactoryMethods = null;
}
//在非宽松策略下
//如果遇到权重相等的(参数个数相等) 也就是存在歧义 将有歧义的构造函数添加进集合
//显式忽略被覆盖的方法(具有相同的参数签名)
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);
}
}
}
//如果没有找到factoryMethod 或者 参数为null 根据情况抛出异常
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);
}
//mbd内省 factoryMethod
if (explicitArgs == null && argsHolderToUse != null) {
mbd.factoryMethodToIntrospect = factoryMethodToUse;
//缓存并置处理标志位为true
argsHolderToUse.storeCache(mbd, factoryMethodToUse);
}
}
//开始实例化并将实例注入到bw的属性当中
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, factoryMethodToUse, argsToUse));
return bw;
}private Object instantiate(String beanName, RootBeanDefinition mbd,
@Nullable Object factoryBean, Method factoryMethod, Object[] args) {
//获取实例化策略然后进行实例化
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 {
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);
}
}
InstantiationStrategy- instantiate(一)
Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
@Nullable Object factoryBean, Method factoryMethod, Object... args)
throws BeansException;
SimpleInstantiationStrategy – instantiate(一)
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
@Nullable Object factoryBean, final Method factoryMethod, Object... args) {
try {
//利用ReflectionUtils反射将factoryMethod设置为可执行的
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
ReflectionUtils.makeAccessible(factoryMethod);
return null;
});
}
else {
ReflectionUtils.makeAccessible(factoryMethod);
}
//ThreadLocal的运用 针对ThreadLocal在Spring中的运用在后面的章节会分析
Method priorInvokedFactoryMethod = currentlyInvokedFactoryMethod.get();
try {
currentlyInvokedFactoryMethod.set(factoryMethod);
//反射invoke执行方法 生成实例
Object result = factoryMethod.invoke(factoryBean, args);
if (result == null) {
result = new NullBean();
}
return result;
}
finally {
if (priorInvokedFactoryMethod != null) {
currentlyInvokedFactoryMethod.set(priorInvokedFactoryMethod);
}
else {
currentlyInvokedFactoryMethod.remove();
}
}
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(factoryMethod,
"Illegal arguments to factory method '" + factoryMethod.getName() + "'; " +
"args: " + StringUtils.arrayToCommaDelimitedString(args), ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(factoryMethod,
"Cannot access factory method '" + factoryMethod.getName() + "'; is it public?", ex);
}
catch (InvocationTargetException ex) {
String msg = "Factory method '" + factoryMethod.getName() + "' threw exception";
if (bd.getFactoryBeanName() != null && owner instanceof ConfigurableBeanFactory &&
((ConfigurableBeanFactory) owner).isCurrentlyInCreation(bd.getFactoryBeanName())) {
msg = "Circular reference involving containing bean '" + bd.getFactoryBeanName() + "' - consider " +
"declaring the factory method as static for independence from its containing instance. " + msg;
}
throw new BeanInstantiationException(factoryMethod, msg, ex.getTargetException());
}
}上面的代码主要功能是在FactoryMethodName不为null的情况下 尝试根据显式参数或者XML配置的参数来找到差别权重最小的factoryMethod，并通过反射执行生成实例。那接下来我们再次回到当FactoryMethodName为null的情况
createBeanInstance(二)
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
...
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
//当再次创建相同的bean时短路
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
//如果resolved为true 而且构造参数也进行过解析
//那么就将参数自动装配进构造器再生成实例
return autowireConstructor(beanName, mbd, null, null);
}
else {
//如果参数未处理(没有参数)则默认构造函数构造
return instantiateBean(beanName, mbd);
}
}
...
}
autowireConstructor (构造方式之一)
protected BeanWrapper autowireConstructor(
String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] ctors, @Nullable Object[] explicitArgs) {
return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
}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) {
//从缓存里找到resolvedConstructorOrFactoryMethod
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
if (argsToResolve != null) {
//解析参数类型 如给定方法的构造函数A(int,int) 则是通过此方法后就会把配置中的
//("1","1") 转换成(1,1)
argsToUse = resolvePreparedArguments(beanName, mbd, bw, constructorToUse, argsToResolve, true);
}
}
if (constructorToUse == null || argsToUse == null) {
// Take specified constructors, if any.
Constructor<?>[] candidates = chosenCtors;
if (candidates == null) {
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);
}
}
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;
}
}
// 候选者长度大于1 或者显式参数不为null 或者mbd已配置参数
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();
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
AutowireUtils.sortConstructors(candidates);
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Constructor<?>> ambiguousConstructors = null;
LinkedList<UnsatisfiedDependencyException> causes = null;
//遍历候选者Constructor找出最适合的构造器
for (Constructor<?> candidate : candidates) {
Class<?>[] paramTypes = candidate.getParameterTypes();
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;
}
//这里可能有人会有疑问 上面的情况不是会跳出循环的吗 这句代码的意义何在呢？
//首先根据排序的条件 修饰符 > 参数个数
//如果能在public修饰符找到参数个数相等并且符合的时候,
//那么后面遇到的参数个数不相等或者修饰符不为public的就不需要再处理
//这句代码用于修饰符的过渡。
if (paramTypes.length < minNrOfArgs) {
continue;
}
//下面的代码与 分析FactoryMethod来构造实例类似
ArgumentsHolder argsHolder;
if (resolvedValues != null) {
try {
//从注释上获取参数名称
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);
}
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 (paramTypes.length != 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;
}
instantiateBean(构造方式之二)
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 {
//获取实例化策略
//这里需要提一下 这里用到了策略模式 后面会结合设计模式来分析源码
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);
}
}
InstantiationStrategy- instantiate(二)
Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner)
throws BeansException;
SimpleInstantiationStrategy – instantiate(二)
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// 如果没有需要方法需要重写则不需要用CGLIB
if (!bd.hasMethodOverrides()) {
Constructor<?> constructorToUse;
synchronized (bd.constructorArgumentLock) {
constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {
//从Class获取Constructor
final Class<?> clazz = bd.getBeanClass();
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
if (System.getSecurityManager() != null) {
constructorToUse = AccessController.doPrivileged(
(PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
}
else {
constructorToUse = clazz.getDeclaredConstructor();
}
//缓存Constructor
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
//使用BeanUtils 并且调用constructor的newInstance方法
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// Must generate CGLIB subclass.
return instantiateWithMethodInjection(bd, beanName, owner);
}
}
createBeanInstance(三)
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
...
// 如果没有被解析过 则需要确定使用哪个构造函数
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// 获取默认的首选构造器(这个方法被GenericApplicationContext的
//内部类ClassDerivedBeanDefinition实现)
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
//没有特定的处理方法 使用无参构造器创建实例
return instantiateBean(beanName, mbd);
}
doCreateBean(二)
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
...
//实例化完成 从包装类 获取 实体Object 和 beanType
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
//MergedBeanDefinitionPostProcessors
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
//将实例化创建的bean提前暴露到SingleFactory
//用于解析单例模式下的循环依赖
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
//lambda表达式 实现ObjectFactory 的 getObject方法
//并将getEarlyBeanReference作为回调方法
//最终回调方法返回的Object添加进第三级缓存SingleObjectFactory中
//getEarlyBeanReference AOP就是在这里将advice动态织如bean中，若没有
//则直接返回bean，不做任何处理
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
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);
}
}
...
}
getEarlyBeanReference
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
Object exposedObject = bean;
//方法本身没有太多逻辑
//除了后处理器的调用外没有别的处理工作
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
}
}
}
return exposedObject;
}
分析：
autowireConstructor
我们总览一下整个函数，其实现的功能考虑以下几个方面。
(1)构造函数的参数的确定
* 根据explicitArgs参数判断
如果传入的参数explicitArgs不为空，那么可以直接确定参数，因为explicitArgs参数是在调用Bean的时候用户指定的，在BeanFactory类中存在这样的方法
Object getBean(String name,Object… args) throw BeansException;
在获取bean的时候，用户不但可以指定bean的名称还可以指定bean所对应类的构造函数或者工厂方法的方法参数，主要用于静态工厂方法的调用，而这里是需要给定完全匹配的参数。所以，可以判断，如果传入参数explicitArgs不为空，则可以确定构造函数就是它。
*缓存中获取参数
除此之外，确定参数的方法如果之前已经分析过，也就是说构造函数参数已经记录在缓存中，那么可以直接拿来使用。而且，这里要提到的是，在缓存中缓存的可能是参数的最终类型也可能是参数的初始类型，例如构造函数参数要求的是int类型，但是原始的参数值可能是String类型的“1”，那么即使在缓存中得到了参数，也需要经过类型转换器的过滤以确保参数类型与对应的构造函数参数类型完全对应
*配置文件获取
如果不能根据传入的参数explicitArgs确定构造函数的参数也无法在缓存中得到相关信息，那么只能开始新一轮的分析
分析从获取配置文件中配置的构造函数信息开始，经过之前的分析，我们知道，Spring中配置文件中的信息经过转换都通过BeanDefinition实例承载，也就是参数mbd中包含，那么可以通过mbd.getConstructorArgumentValues()来获取配置的构造函数信息。有了配置信息便可以获取对应的参数值信息了，获取函数值的信息包括直接指定值，如:直接指定构造函数中某个值为原始类型String类型，或者是一个对其他bean的引用，而这一处理委托给resolveConstructorArguments方法，并返回能解析到的参数的个数。
(2)构造函数的确定
经过了第一步后已经确定了构造函数的参数，接下来的任务就是根据构造函数参数在所有构造函数中锁定对应的构造函数，而匹配的发方法就是根据参数个数匹配，所以在匹配之前需要先对构造函数按照public构造函数优先参数数量降序、非public构造函数参数数量降序。这样可以在遍历的情况下迅速判断排在后面的构造函数参数个数是否符合条件。
由于在配置并不是唯一限制使用使用参数位置索引的方式去创建，同样还支持指定参数名称进行设定参数值的情况，如<constructor-arg name=”aa”>,那么这种情况就需要首先确定构造函数中的名称。
获取参数名称的那个可以有两种方式，一种是通过注解的方式直接获取，另一种就是使用Spring中提供的工具类ParameterNameDiscoverer来获取。构造函数、参数名称、参数类型、参数值确定后锁定构造函数以及转换对应的参数类型。
(3)根据确定的构造函数转换对应的参数类型
主要是使用Spring中提供的类型转换器或者用户提供的自定义类型转换器来进行转换
(4)构造函数不确定性的验证
当然，有时候即使构造函数、参数名称、参数类型、参数值都确定后也不一定会直接锁定构造函数，不同构造函数的参数为父子关系，所以Spring在最后又做了一次验证
(5)根据实例化策略以及得到的构造函数以及构造函数参数实例化
instantiate(二)
Spring为了能更方便做了大量的工作，程序中如果判断beanDefinition.getMethodOverrides()为空也就是用户没有使用replace或者lookup的配置方法，那么直接使用反射的方式，简单快捷，但是如果使用了这两个特性，在直接使用反射的方式创建实例就不妥了，因为需要这两个配置提供的功能切入进去，所以就必须使用动态代理的方式将包含这两个特性所对应的逻辑的拦截增强器设置进去，这样才可以保证在调用方法的时候会被相应的拦截器增强，返回值为包含拦截器的代理实例
下一章节我们分析Bean的属性填充
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