在上篇spring容器之开启bean的创建之旅中我们最后将创建bean的过程大致的总结了分八步走,这里就不啰嗦了,不知道的可以自己去看看,本篇主要的学习是对上节创建bean的每个步骤进行详细的学习,首先我们从创建bean的实例开始,代码如下:
AbstractAutowireCapableBeanFactory.java
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
//解析class
Class<?> beanClass = resolveBeanClass(mbd, beanName);
//校验
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());
}
//<1>.获取创建bean实例的回调Supplier
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
//如果存在该回调,使用该回调策略来初始化bean实例
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
//<2>.如果工厂方法不为null,则使用工厂的方法的策略来初始化bean实例
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
//<3>. Shortcut when re-creating the same bean...
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
//使用constructorArgumentLock
//该constructorArgumentLock为构造函数字段常用的锁
synchronized (mbd.constructorArgumentLock) {
//<3.1>.resolvedConstructorOrFactoryMethod用来缓存已解析的构造函数的字段和或工厂方法
//如果不为null
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
//对该构造参数进行标记为已解析
//因为对于一个类可能有很多个构造函数,每个构造函数所需的参数可能不一样,所以在调用前需确定其参数方可
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
//如果解析完成,直接通过注入即可
if (resolved) {
//<3.2>.构造函数自动注入
if (autowireNecessary) {
return autowireConstructor(beanName, mbd, null, null);
}
else {
//<3.3>.使用默认构造函数进行构造
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
//<4>.通过参数来解析构造器
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
//<4.1>.当args不为null时,通过参数的个数,类型等,做精确的构造方法的选择来创建bean
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
//<4.2>.获取构造方法来构建bean
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
//<4.3>.使用默认的构造函数构造
return instantiateBean(beanName, mbd);
}
方法很长,但总体来说目的很明确,这里简单的小结一下:
- 在<1>处,我们可以看到对创建bean实例过程中回调的获取
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
//如果存在该回调,使用该回调策略来初始化bean实例
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
当获取到的回调不为null时,发现调用#obtainFromSupplier(Supplier<?> instanceSupplier, String beanName)来初始化,跟踪代码来到:
看代码之前先来了解一个java8里的特性Supplier<?>接口的东西,让大家有个认识,说实话好久没接触过了,直接看代码:
@FunctionalInterface
public interface Supplier<T> {
/**
* Gets a result.
*
* @return a result
*/
T get();
}
Supplier实际上是一个供给接口,且只有一个get()方法,其实类似于spring的工厂方法.
AbstractBeanDefinition.java
private Supplier<?> instanceSupplier;
public void setInstanceSupplier(@Nullable Supplier<?> instanceSupplier) {
this.instanceSupplier = instanceSupplier;
}
/**
* Return a callback for creating an instance of the bean, if any.
* @since 5.0
*/
@Nullable
public Supplier<?> getInstanceSupplier() {
return this.instanceSupplier;
}
在AbstractBeanDefinition类中可以看到它的实例化过程,接下来我们来看回调的整个过程:
/**保存当前创建bean的名字*/
private final NamedThreadLocal<String> currentlyCreatedBean = new NamedThreadLocal<>("Currently created bean");
protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String beanName) {
Object instance;
//获取原先创建bean的名字
String outerBean = this.currentlyCreatedBean.get();
//保存新的bean的名字到currentlyCreatedBean中
this.currentlyCreatedBean.set(beanName);
try {
//1.调用Supplier#get()方法获取bean实例
instance = instanceSupplier.get();
}
finally {
if (outerBean != null) {
//如果原先bean存在,将保存到currentlyCreatedBean中
this.currentlyCreatedBean.set(outerBean);
}
else {
this.currentlyCreatedBean.remove();
}
}
//2.如果没有创建对象时,则创建一个NullBean实例
if (instance == null) {
instance = new NullBean();
}
//3.初始化BeanWrapper对象
BeanWrapper bw = new BeanWrapperImpl(instance);
initBeanWrapper(bw);
return bw;
}
简单的总结一下:
- 调用我们指定的Supplier的get()方法获取bean的实例
- 进行一些相关的设置操作
- 如果没有创建对象,直接创建一个NullBean对象.
- 最后是对BeanWrapper对象的创建以及初始化的操作
- 在<2>处,我们可以看到的是,如果存在工厂方法,则通过#instantiateUsingFactoryMethod(String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs)方法来完成bean的初始化过程,直接看代码:
AbstractAutowireCapableBeanFactory.java
protected BeanWrapper instantiateUsingFactoryMethod(
String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
return new ConstructorResolver(this).instantiateUsingFactoryMethod(beanName, mbd, explicitArgs);
}
我们可以方法首先需要构造一个ConstructorResolver对象,然后调用该实例的#instantiateUsingFactoryMethod(String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs)方法构建bean实例,接着看:
ConstructorResolver.java
public BeanWrapper instantiateUsingFactoryMethod(
String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
//1.构建并实例化BeanWrapperImpl对象
BeanWrapperImpl bw = new BeanWrapperImpl();
this.beanFactory.initBeanWrapper(bw);
//2.获取factoryBean factoryClass和isStatic等属性
Object factoryBean;
Class<?> factoryClass;
boolean isStatic;
//2.1.获取factoryBeanName属性
String factoryBeanName = mbd.getFactoryBeanName();
//factoryBeanName存在,且跟当前bean的名字一样,直接抛BeanDefinitionStoreException异常
if (factoryBeanName != null) {
if (factoryBeanName.equals(beanName)) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"factory-bean reference points back to the same bean definition");
}
//不一样的情况下
//2.2.获取factory实例
factoryBean = this.beanFactory.getBean(factoryBeanName);
if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {
throw new ImplicitlyAppearedSingletonException();
}
//2.3.获取factoryClass属性
factoryClass = factoryBean.getClass();
isStatic = false;
}
//2.3.此处可能是静态工厂方法
//因为静态工厂创建bean时,需要提供工厂的全类名
else {
// 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.获取工厂属性factoryMethodToUse ArgumentsHolder和argsToUse
Method factoryMethodToUse = null;//工厂方法
ArgumentsHolder argsHolderToUse = null;
Object[] argsToUse = null;//参数
//3.1.explicitArgs参数通过getBean方法传入
//如果在构建bean时指定了构造器,那么直接使用该参数
if (explicitArgs != null) {
argsToUse = explicitArgs;
}
//3.2.没有指定的话,尝试着从配置文件中解析
else {
Object[] argsToResolve = null;
//给公用构造方法加锁
synchronized (mbd.constructorArgumentLock) {
//从缓存中尝试着获取
factoryMethodToUse = (Method) mbd.resolvedConstructorOrFactoryMethod;
//从缓存中获取argsToUse属性
if (factoryMethodToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached factory method...
argsToUse = mbd.resolvedConstructorArguments;
//从缓存中没有获取到
if (argsToUse == null) {
//获取构造函数的可见字段
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
//3.3.缓存中存在
//解析在beanDefinition中的参数类型,解析的过程大致如下:
//如给定方法的构造函数 A(int ,int )，则通过此方法后就会把配置文件中的("1","1")转换为 (1,1)
//缓存中的值可能是原始值也有可能是最终值
if (argsToResolve != null) {
argsToUse = resolvePreparedArguments(beanName, mbd, bw, factoryMethodToUse, argsToResolve, true);
}
}
//4.没有被缓存
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.
//4.1.获取全限定名
factoryClass = ClassUtils.getUserClass(factoryClass);
List<Method> candidateList = null;
//4.2.检测方法名是否是唯一性
if (mbd.isFactoryMethodUnique) {
if (factoryMethodToUse == null) {
factoryMethodToUse = mbd.getResolvedFactoryMethod();
}
if (factoryMethodToUse != null) {
candidateList = Collections.singletonList(factoryMethodToUse);
}
}
if (candidateList == null) {
candidateList = new ArrayList<>();
//4.3.获取所有符合条件的方法
Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
//遍历符合条件是static的方法那么就添加到candidateList中
for (Method candidate : rawCandidates) {
if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {
candidateList.add(candidate);
}
}
}
//4.4创建bean实例
if (candidateList.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {
Method uniqueCandidate = candidateList.get(0);
if (uniqueCandidate.getParameterCount() == 0) {
//缓存内省工厂方法
mbd.factoryMethodToIntrospect = uniqueCandidate;
synchronized (mbd.constructorArgumentLock) {
mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;
mbd.constructorArgumentsResolved = true;
mbd.resolvedConstructorArguments = EMPTY_ARGS;
}
//封装bean
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, uniqueCandidate, EMPTY_ARGS));
return bw;
}
}
Method[] candidates = candidateList.toArray(new Method[0]);
//对构造的工厂方法进行排序
//排序规则是:优先是public的,之后是非公共的
AutowireUtils.sortFactoryMethods(candidates);
ConstructorArgumentValues resolvedValues = null;
boolean autowiring = (mbd.getResolvedAutowireMode() == AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR);
int minTypeDiffWeight = Integer.MAX_VALUE;
Set<Method> ambiguousFactoryMethods = null;
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.
//4.5.获取构造函数的参数
if (mbd.hasConstructorArgumentValues()) {
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
//用来承载解析后的参数的值
resolvedValues = new ConstructorArgumentValues();
//解析参数
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
else {
minNrOfArgs = 0;
}
}
//4.6.遍历方法
LinkedList<UnsatisfiedDependencyException> causes = null;
for (Method candidate : candidates) {
//获取方法体上的参数
Class<?>[] paramTypes = candidate.getParameterTypes();
//
if (paramTypes.length >= minNrOfArgs) {
//保存参数对象
ArgumentsHolder argsHolder;
//explicitArgs为getBean方法的参数
if (explicitArgs != null) {
// Explicit arguments given -> arguments length must match exactly.
//显示给定参数,参数的长度必须匹配
if (paramTypes.length != explicitArgs.length) {
continue;
}
//根据参数去构建参数的持有者ArgumentsHolder对象
argsHolder = new ArgumentsHolder(explicitArgs);
}
//构建bean的explicitArgs为null
else {
// Resolved constructor arguments: type conversion and/or autowiring necessary.
//为了提供必须的参数,解析参数
try {
String[] paramNames = null;
//获取ParameterNameDiscoverer对象
//ParameterNameDiscoverer为解析方法和构造函数的参数的接口
ParameterNameDiscoverer pnd = this.beanFactory.getParameterNameDiscoverer();
//如果存在,获取构造器的所有参数
if (pnd != null) {
paramNames = pnd.getParameterNames(candidate);
}
//在给定已解析的构造函数参数值的情况下，创建一个参数ArgumentsHolder的持有者对象
argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw,
paramTypes, paramNames, candidate, autowiring, candidates.length == 1);
}
//在创建的过程中,如果抛UnsatisfiedDependencyException异常,保存到causes中
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);
//继续执行
continue;
}
}
//5.通过isLenientConstructorResolution来判断解析的构造方法是宽松模式还是严格模式
//如果是宽松模式:采用最接近的来匹配解析
//如果是严格模式:所有的都要匹配上才可以
//typeDiffWeight:获取类型差异权重
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// Choose this factory method if it represents the closest match.
//匹配最接近的构造函数,以下为作为该构造函数的参数
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).
// 如果具有相同参数数量的方法具有相同的类型差异权重，则收集此类型选项
// 但是，仅在非宽松构造函数解析模式下执行该检查，并显式忽略重写方法（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())) {
//获取到多个可以匹配的方法
if (ambiguousFactoryMethods == null) {
ambiguousFactoryMethods = new LinkedHashSet<>();
ambiguousFactoryMethods.add(factoryMethodToUse);
}
ambiguousFactoryMethods.add(candidate);
}
}
}
//6. 没有可执行的方法时,直接抛UnsatisfiedDependencyException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);
//遍历explicitArgs参数数组
if (explicitArgs != null) {
for (Object arg : explicitArgs) {
//如果遍历到的参数不为null,获取参数名,然后保存,为null,直接保存null即可
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);
}
}
//对argTypes进行转换
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);
}
//将解析后的构造函数保存到缓存中
if (explicitArgs == null && argsHolderToUse != null) {
mbd.factoryMethodToIntrospect = factoryMethodToUse;
argsHolderToUse.storeCache(mbd, factoryMethodToUse);
}
}
//创建bean对象,并保存到bw中
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, factoryMethodToUse, argsToUse));
return bw;
}
呜呜呜,这个方法好长呀,看的也是懵逼,硬着头皮看的,而且过程也很复杂,我看完之后也没啥影响了,再来一遍,好像在方法的整个过程中,都是对工厂对象的构造函数和参数展开,通过匹配最接近的构造函数,在方法的末尾调用#instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner, Constructor<?> ctor, Object... args) 方法来建bean对象.我们在对该方法进行总结一下:
- 在1.处是首先是对BeanWrapperImpl对象的创建和初始化,以备后面bean的创建完成后进行封装
- 在2.处,获取工厂bean的一些参数和方法,如:factoryBeanName和factoryClass和isStatic等属性
- 在2.1.处是对factoryBeanName的获取以及简单的处理操作
String factoryBeanName = mbd.getFactoryBeanName();
//factoryBeanName存在,且跟当前bean的名字一样,直接抛BeanDefinitionStoreException异常
if (factoryBeanName != null) {
if (factoryBeanName.equals(beanName)) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"factory-bean reference points back to the same bean definition");
}
我们可以看到是通过beanDefinition来获取factoryBean的name属性,这也是符合的,我们知道beanDefinition就是描述一个bean的定义
- 在2.2.处是获取factory实例
factoryBean = this.beanFactory.getBean(factoryBeanName);
if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {
throw new ImplicitlyAppearedSingletonException();
}
是通过#getBean()来获取的,此方法最后是通过AbstractAutowireCapableBeanFactory#getBean(String name)来实现,关于此方法的学习我们前面已经说了,这里就不啰嗦了,这里我们需要注意的一点是:
上述获取到的factory是因为工厂的方法不为null的情况下.再来看另外一种情况.
- 2.3.处,那么就是一个静态工厂了,需要提供类的全限定名才能获取factory对象
- 在3.处实际上是对工厂工造参数的确定,其主要是通过explicitArgs是否为null来判断
注意:explicitArgs主要是我们在调用#getBean方法时,由用户直接指定构造函数来创建对象的参数,它不为null,那么我们的构造函数就确认了
- 在3.2处,当explicitArgs为null时,从配置文件中解析获取
.....省略很多代码.....
Object[] argsToResolve = null;
//给公用构造方法加锁
synchronized (mbd.constructorArgumentLock) {
//从缓存中尝试着获取
factoryMethodToUse = (Method) mbd.resolvedConstructorOrFactoryMethod;
//从缓存中获取argsToUse属性
if (factoryMethodToUse != null && mbd.constructorArgumentsResolved) {
// Found a cached factory method...
argsToUse = mbd.resolvedConstructorArguments;
//从缓存中没有获取到
if (argsToUse == null) {
//获取构造函数的可见字段
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
都是从我们的beanDefinition中尝试着获取,简单的来说一下:
<1>. 首先是从resolvedConstructorOrFactoryMethod获取,该缓存主要保存的是已经解析过的构造方法或者是工厂方法
<2> . 从resolvedConstructorArguments中获取已经完全解析的构造函数的参数
<3>. 从preparedConstructorArguments中获取已经准备好的部分构造参数以备构造方法使用
- 在3.3.处,上述的参数我们在缓存中获取到了,解析部分构造函数所需的参数,调用#resolvePreparedArguments(String beanName, RootBeanDefinition mbd, BeanWrapper bw,Executable executable, Object[] argsToResolve, boolean fallback)方法来完成
if (argsToResolve != null) {
argsToUse = resolvePreparedArguments(beanName, mbd, bw, factoryMethodToUse, argsToResolve, true);
}
当argsToResolve存在的情况下,接着看:
private Object[] resolvePreparedArguments(String beanName, RootBeanDefinition mbd, BeanWrapper bw,
Executable executable, Object[] argsToResolve, boolean fallback) {
//获取TypeConverter对象
TypeConverter customConverter = this.beanFactory.getCustomTypeConverter();
//存在的话,就用自定义的TypeConverter,不存在的话用BeanWrapper来代替
TypeConverter converter = (customConverter != null ? customConverter : bw);
//这里的beanFactory为AbstractAutowireCapableBeanFactory
//构建BeanDefinitionValueResolver解析器
BeanDefinitionValueResolver valueResolver =
new BeanDefinitionValueResolver(this.beanFactory, beanName, mbd, converter);
//获取参数的类型
Class<?>[] paramTypes = executable.getParameterTypes();
//解析处理过程
Object[] resolvedArgs = new Object[argsToResolve.length];
for (int argIndex = 0; argIndex < argsToResolve.length; argIndex++) {
Object argValue = argsToResolve[argIndex];
//通过参数的索引和构造函数来创建MethodParameter对象
MethodParameter methodParam = MethodParameter.forExecutable(executable, argIndex);
//解析参数的类型
GenericTypeResolver.resolveParameterType(methodParam, executable.getDeclaringClass());
//argValue是AutowiredArgumentMarker
//调用resolveAutowiredArgument去解析处理
if (argValue instanceof AutowiredArgumentMarker) {
argValue = resolveAutowiredArgument(methodParam, beanName, null, converter, fallback);
}
//如果是BeanMetadataElement类型的
//调用resolveValueIfNecessary去解析处理
else if (argValue instanceof BeanMetadataElement) {
argValue = valueResolver.resolveValueIfNecessary("constructor argument", argValue);
}
//字符串类型的
//通过AbstractAutowireCapableBeanFactory#evaluateBeanDefinitionString方法去处理
else if (argValue instanceof String) {
argValue = this.beanFactory.evaluateBeanDefinitionString((String) argValue, mbd);
}
//保存
Class<?> paramType = paramTypes[argIndex];
try {
//对解析后的参数进行转换
//规则为:如给定方法的构造函数 A(int ,int )，则通过此方法后就会把配置文件中的("1","1")转换为 (1,1)
resolvedArgs[argIndex] = converter.convertIfNecessary(argValue, paramType, methodParam);
}
catch (TypeMismatchException ex) {
throw new UnsatisfiedDependencyException(
mbd.getResourceDescription(), beanName, new InjectionPoint(methodParam),
"Could not convert argument value of type [" + ObjectUtils.nullSafeClassName(argValue) +
"] to required type [" + paramType.getName() + "]: " + ex.getMessage());
}
}
return resolvedArgs;
}
在该方法的最后我们发现,对于不同类型的参数类型,对应着不同的处理方法.
最后进行参数的转化
- 在4处,如果工厂没有被缓存,可能是静态工厂
- 4.1.处首先是获取factory的全限定名并进行唯一性的检查
- 4.3.处获取所有符合条件的方法
Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
//遍历符合条件是static的方法那么就添加到candidateList中
for (Method candidate : rawCandidates) {
if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {
candidateList.add(candidate);
}
}
- 在4.4处创建bean对象并封装
List<Method> candidateList = null;
if (candidateList.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {
Method uniqueCandidate = candidateList.get(0);
if (uniqueCandidate.getParameterCount() == 0) {
//缓存内省工厂方法
mbd.factoryMethodToIntrospect = uniqueCandidate;
synchronized (mbd.constructorArgumentLock) {
mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;
mbd.constructorArgumentsResolved = true;
mbd.resolvedConstructorArguments = EMPTY_ARGS;
}
//封装bean
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, uniqueCandidate, EMPTY_ARGS));
return bw;
}
}
在此处是创建bean实例的地方,核心方法#instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner, Object factoryBean, final Method factoryMethod, @Nullable Object... args)来创建,因为我们的工厂对象以及构造函数和参数已经确定了,接着看:
private Object instantiate(String beanName, RootBeanDefinition mbd,
@Nullable Object factoryBean, Method factoryMethod, Object[] args) {
try {
//首先是获取当前系统的安全环境管理器
//存在的话在当前环境下创建
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged((PrivilegedAction<Object>) () ->
this.beanFactory.getInstantiationStrategy().instantiate(
mbd, beanName, this.beanFactory, factoryBean, factoryMethod, args),
this.beanFactory.getAccessControlContext());
}
//直接创建
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);
}
}
我们可以发现首先是对系统的当前环境的检测,如:是否有访问权限等,然后真正的核心创建bean实例的方法是InstantiationStrategy#instantiate()方法,接着看:
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,
@Nullable Object factoryBean, final Method factoryMethod, Object... args) {
try {
//设置方法的访问权限
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
ReflectionUtils.makeAccessible(factoryMethod);
return null;
});
}
else {
ReflectionUtils.makeAccessible(factoryMethod);
}
//获取之前的方法
Method priorInvokedFactoryMethod = currentlyInvokedFactoryMethod.get();
try {
//将新的工厂方法保存到currentlyInvokedFactoryMethod中
currentlyInvokedFactoryMethod.set(factoryMethod);
//创建bean对象
Object result = factoryMethod.invoke(factoryBean, args);
//没创建成功,则创建一个nullBean来代替
if (result == null) {
result = new NullBean();
}
//创建成功的话,直接返回
return result;
}
finally {
if (priorInvokedFactoryMethod != null) {
//覆盖之前的方法
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());
}
}
该方法其实就一个核心点,通过反射的方式来创建对象
Object result = factoryMethod.invoke(factoryBean, args);
其实到这一步了我们的目标也达到了,后面的无非还是一些参数的验证和匹配最接近的构造函数,最后还是调用#instantiate来创建bean对象,其中包括一些解析参数的方法如:#resolveConstructorArguments()方法和#createBeanInstance(...)方法可以去看看,我这里就不说了,那么关于创建bean实例的篇幅就到这里了
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