spring源码bean生命周期篇 一 如何实例化对象
当前源码springboot版本为2.1.6.RELEASE ，spring版本为5.1.8.RELEASE
代码粘贴的也只有相关重要部分,如果是需要全部的代码请看源码
章节内容
(1) spring的创建流程是怎么样的?实例化是哪个环节？
(2)推断构造方法
(3)工厂方法实例化bean（@Bean注解原理是什么的？)
(4)构造参数实例化bean（@Autowired作用到构造方法原理是什么？)
spring创建bean的流程图
-
在创建bean之前，首先要找到对应的类并且加载
-
合并bean定义（当前流程图省去）
-
实例化前（执行 InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation方法）
-
实例化
-
实例化后（执行InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation方法）
-
为属性赋值（执行InstantiationAwareBeanPostProcessor.postProcessProperties，InstantiationAwareBeanPostProcessor.postProcessPropertyValue后得到返回后进行applyPropertyValue方法如上图所示）
-
执行Aware接口的对应方法（invokeAwareMethods）
-
初始化前（执行BeanPostProcessor.postProcessBeforeInitialization方法）
- 初始化（ 执行初始化方法）
-
出初始化后(执行BeanPostProcessor.postProcessAfterInitialization方法）
整个流程图对应代码的位置： org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean
本章节事讲解当前流程的第四步骤 实例化
一.@Bean注解的对象实例化
1.解析@Bean
package com.example.demo1;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class A {
@Bean
public static B b(){
return new B();
}
@Bean
public C c(){
return new C();
}
}
org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry方法中会对配置类A只所有的@Bean注解进行解析
对静态方法方法b进行解析，根据结果加载B的beanDefintion ，设置BeanDefintion的factoryMethodName属性为 "b"，beanClassName为com.example.demo1.A
对于非静态方法c解析，根据结果加载C的beanDefinition，设置FactoryMethodName为c,factoryBeanName为a
我们看看ConfigurationClassPostProcessor进行@bean解析以及处理的调用链
org.springframework.context.annotation.ConfigurationClassPostProcessor
postProcessBeanDefinitionRegistry()
postProcessBeanDefinitionRegistry()
org.springframework.context.annotation.ConfigurationClassPostProcessor
processConfigBeanDefinitions()
processConfigBeanDefinitions()
org.springframework.context.annotation.ConfigurationClassParser
parse()
parse()
org.springframework.context.annotation.ConfigurationClassParser
processConfigurationClass()
processConfigurationClass()
org.springframework.context.annotation.ConfigurationClassParser
doProcessConfigurationClass()
doProcessConfigurationClass()
org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader
loadBeanDefinitions()
loadBeanDefinitions()
org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader
loadBeanDefinitionsForConfigurationClass()
loadBeanDefinitionsForConfigurationClass()
org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader
loadBeanDefinitionsForBeanMethod()
loadBeanDefinitionsForBeanMethod()
org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions
- parser.parse解析配置类的注解，这其中就包含对@Bean的解析，并把结果放入ConfigurationClass
- reader.loadBeanDefintion会加载@Bean修饰的方法返回类型的beanDefintion
org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass()
// Process individual @Bean methods
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
inal class BeanMethod extends ConfigurationMethod {
public BeanMethod(MethodMetadata metadata, ConfigurationClass configurationClass) {
super(metadata, configurationClass);
}
}
abstract class ConfigurationMethod
public ConfigurationMethod(MethodMetadata metadata, ConfigurationClass configurationClass) {
this.metadata = metadata;
this.configurationClass = configurationClass;
}
}
org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForBeanMethod()
//org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitions()
public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) {
TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();
for (ConfigurationClass configClass : configurationModel) {
loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);
}
}
//org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader
loadBeanDefinitions()
private void loadBeanDefinitionsForConfigurationClass(
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
loadBeanDefinitionsForBeanMethod(beanMethod);
}
}
private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {
ConfigurationClass configClass = beanMethod.getConfigurationClass();
MethodMetadata metadata = beanMethod.getMetadata();
//获取方法@Bean方法的名称
String methodName = metadata.getMethodName();
ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass, metadata);
if (metadata.isStatic()) {
// static @Bean method，上图例子方法b会走当前代码
//例子中beanClassName为com.example.demo1.A
beanDef.setBeanClassName(configClass.getMetadata().getClassName());
//例子中methodName为b
beanDef.setFactoryMethodName(methodName);
}
else {
// instance @Bean method 方法c会走当前代码
//例子中factoryBeanName为a
beanDef.setFactoryBeanName(configClass.getBeanName());
//例子中methodName为c
beanDef.setUniqueFactoryMethodName(methodName);
}
}
//注册到spring的BeanDefinition容器中
this.registry.registerBeanDefinition(beanName, beanDefToRegister);
}
public void setUniqueFactoryMethodName(String name) {
Assert.hasText(name, "Factory method name must not be empty");
setFactoryMethodName(name);
this.isFactoryMethodUnique = true;
}
2.@Bean实例化
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory
createBean()
createBean()
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory
doCreateBean()
doCreateBean()
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory
createBeanInstance()
createBeanInstance()
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory
instantiateUsingFactoryMethod()
instantiateUsingFactoryMethod()
org.springframework.beans.factory.support.ConstructorResolver
instantiateUsingFactoryMethod
instantiateUsingFactoryMethod
1.找出符合条件的工厂方法 ，没有符合条件的工厂方法或者多个符合条件的方法抛出BeanCreateException
2.调用工厂方法，保存返回值
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean()
/**
@Override
public Object getBean(String name, Object... args) throws BeansException {
return doGetBean(name, null, args, false);
}
getBean(beanName,args)
args可通过getBean()传入
*/
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
}
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance()
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
}
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod()
/**
explicitArgs getBean(beanName,explicitArgs)指定
**/
public BeanWrapper instantiateUsingFactoryMethod(
String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
BeanWrapperImpl bw = new BeanWrapperImpl();
this.beanFactory.initBeanWrapper(bw);
Object factoryBean;
Class<?> factoryClass;
boolean isStatic;
String factoryBeanName = mbd.getFactoryBeanName();
if (factoryBeanName != null) {
if (factoryBeanName.equals(beanName)) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"factory-bean reference points back to the same bean definition");
}
//获取 com.example.demo1.A类型的bean a
factoryBean = this.beanFactory.getBean(factoryBeanName);
if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {
throw new ImplicitlyAppearedSingletonException();
}
//加载com.example.demo1.A.class
factoryClass = factoryBean.getClass();
//标记bean注解修饰的是非静态方法
isStatic = false;
}
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;
//加载类com.example.demo1.A.class,并标记@Bean修饰的是静态方法
factoryClass = mbd.getBeanClass();
isStatic = true;
}
Method factoryMethodToUse = null;
ArgumentsHolder argsHolderToUse = null;
Object[] argsToUse = null;
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...
argsToUse = mbd.resolvedConstructorArguments;
if (argsToUse == null) {
argsToResolve = mbd.preparedConstructorArguments;
}
}
}
if (argsToResolve != null) {
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);
//获取com.example.demo1.A下所有的方法
Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
List<Method> candidateList = new ArrayList<>();
for (Method candidate : rawCandidates) {
//遍历com.example.demo1.A下所有的方法，选出与beanDefintion设置的factoryMethodName一致的，并且与前面标记@Bean修饰的是否静态方法也是一致的
if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {
candidateList.add(candidate);
}
}
//符合条件的方法只有一个
if (candidateList.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) {
Method uniqueCandidate = candidateList.get(0);
if (uniqueCandidate.getParameterCount() == 0) {
mbd.factoryMethodToIntrospect = uniqueCandidate;
synchronized (mbd.constructorArgumentLock) {
mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;
mbd.constructorArgumentsResolved = true;
mbd.resolvedConstructorArguments = EMPTY_ARGS;
}
//调用bean修饰的方法，获取放返回值放入BeanInstance
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, uniqueCandidate, EMPTY_ARGS));
return bw;
}
}
Method[] candidates = candidateList.toArray(new Method[0]);
//排序，@Bean方法参数多的排在前面
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 {
// 我们没有通过编程方式传入参数，所以我们需要解析，在bean定义中持有的构造函数参数中指定的参数
if (mbd.hasConstructorArgumentValues()) {
//ConstructorArgumentValues 可以通过BeanDefinition.getconstructorArgumentValues()指定
ConstructorArgumentValues cargs = mbd.getConstructorArgumentValues();
resolvedValues = new ConstructorArgumentValues();
minNrOfArgs = resolveConstructorArguments(beanName, mbd, bw, cargs, resolvedValues);
}
else {
minNrOfArgs = 0;
}
}
LinkedList<UnsatisfiedDependencyException> causes = null;
for (Method candidate : candidates) {
Class<?>[] paramTypes = candidate.getParameterTypes();
if (paramTypes.length >= minNrOfArgs) {
ArgumentsHolder argsHolder;
if (explicitArgs != null) {
// Explicit arguments given -> arguments length must match exactly.
if (paramTypes.length != explicitArgs.length) {
continue;
}
argsHolder = new ArgumentsHolder(explicitArgs);
}
else {
// 已解析的构造函数参数:必须进行类型转换或自动装配
try {
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.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;
}
}
//宽松的检查方式使用argsHolder.getTypeDifferenceWeight计算权重，非宽松的方式getAssignabilityWeight计算权重
int typeDiffWeight = (mbd.isLenientConstructorResolution() ?
argsHolder.getTypeDifferenceWeight(paramTypes) : argsHolder.getAssignabilityWeight(paramTypes));
// 选择工厂方法匹配找到的有效参数和入参类型最匹配的
if (typeDiffWeight < minTypeDiffWeight) {
factoryMethodToUse = candidate;
argsHolderToUse = argsHolder;
argsToUse = argsHolder.arguments;
minTypeDiffWeight = typeDiffWeight;
ambiguousFactoryMethods = null;
}
//找出歧义:在相同类型差权的情况下对于具有相同数量参数的方法，收集这样的候选对象并进行计算，最终会引发歧义常。但是，只在非宽松构造函数解析模式下执行该检查，并显式地忽略被覆盖的方法(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) {
//参数个相同，差权一样的方法保存在ambiguousFactoryMethods属性中
ambiguousFactoryMethods = new LinkedHashSet<>();
ambiguousFactoryMethods.add(factoryMethodToUse);
}
ambiguousFactoryMethods.add(candidate);
}
}
}
//没有找到合适的工厂方法
if (factoryMethodToUse == 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") + ".");
}//工厂方法返回类型为void，抛出异常
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);
}
}
Assert.state(argsToUse != null, "Unresolved factory method arguments");
bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, factoryMethodToUse, argsToUse));
return bw;
}
org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate
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();
}
}
}
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());
}
}
二.构造参数对象实例化
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// 确保当前类已经加载
Class<?> beanClass = resolveBeanClass(mbd, beanName);
//检查类是不是public修饰符
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());
}
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
// resolvedConstructorOrFactoryMethod bean定义用于缓存解析的构造函数或者工厂方法的字段
//constructorArgumentsResolved bean定义中用于标记构造函数参数是否已解析的字段
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) {
return autowireConstructor(beanName, mbd, null, null);
}
else {
return instantiateBean(beanName, mbd);
}
}
// 推断构造参数
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
//1.推断构造参数的结果不为null
//2.程序员指定了构造方法入参值，通过getBean()或者BeanDefinition.setconstructorArgumentValues()指定，那就用所匹配的构造方法
//3.程序员想让Spring自动选择构造方法以及沟造方法的入参值， autowire="constructor'
//4.有默认首选的构造方法
//满足三项的任何一项调用的都是autowireConstructor也就是使用
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
return instantiateBean(beanName, mbd);
}
1.推断构造参数
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineConstructorsFromBeanPostProcessors
1.类中有多个@autowired注解，只要有一个required属性为true，但发现类中有其他@autowired注解，不管required属性都为true还是false，都抛出异常
2.只有一个@Autowired注解并且required属性都为true就放入候选构造参数
3.有@Autowired注解并且required属性都为false就都放入候选构造参数，并放入无参构造参数到候选构造参数集合
4.没有Autowired注解只有一个构造函数且有参放入候选构造函数
protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName)
throws BeansException {
if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
if (ctors != null) {
return ctors;
}
}
}
}
return null;
}
org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.determineCandidateConstructors
public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, final String beanName)
throws BeanCreationException {
/**解析lookup注解，获取@lookup修饰的方法，存入bean定义
lookup-method注入
单例模式的bean只会被创建一次，IoC容器会缓存该bean实例以供下次使用；原型模式的bean每次都会创建一个全新的bean，IoC容器不会缓存该bean的实例。那么如果现在有一个单例模式的bean引用了一个原型模式的bean呢？如果无特殊处理，则被引用的原型模式的bean也会被缓存，这就违背了原型模式的初衷，这时使用lookup-method注入可以解决该问题
b.relplace-method
主要作用就是替换方法体及其返回值*/
if (!this.lookupMethodsChecked.contains(beanName)) {
try {
ReflectionUtils.doWithMethods(beanClass, method -> {
Lookup lookup = method.getAnnotation(Lookup.class);
if (lookup != null) {
Assert.state(this.beanFactory != null, "No BeanFactory available");
LookupOverride override = new LookupOverride(method, lookup.value());
try {
// 那么是什么条件才会触发这个MethodOverrides呢？其实是Spring配置文件中的lookup-method和replace-method，
// 这其实是两个方法级别的注入，和一般的属性(Property)注入是不一样的，它们注入的是方法(Method)。
// 两者的差别是这样的,如果需要替换的方法没有返回值，那么只能使用replace-method来替换，而不能用lookup-method来替换。
// replace-method必须实现MethodReplacer接口的Bean才能替换，而lookup-method则由BeanFactory自动为我们处理
RootBeanDefinition mbd = (RootBeanDefinition) this.beanFactory.getMergedBeanDefinition(beanName);
mbd.getMethodOverrides().addOverride(override);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(beanName,
"Cannot apply @Lookup to beans without corresponding bean definition");
}
}
});
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName, "Lookup method resolution failed", ex);
}
this.lookupMethodsChecked.add(beanName);
}
// 缓存里面有构造方法
Constructor<?>[] candidateConstructors = this.candidateConstructorsCache.get(beanClass);
if (candidateConstructors == null) {
// Fully synchronized resolution now...
synchronized (this.candidateConstructorsCache) {
candidateConstructors = this.candidateConstructorsCache.get(beanClass);
if (candidateConstructors == null) {
Constructor<?>[] rawCandidates;
try {
//2.获得当前类所有的构造方法
rawCandidates = beanClass.getDeclaredConstructors();
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Resolution of declared constructors on bean Class [" + beanClass.getName() +
"] from ClassLoader [" + beanClass.getClassLoader() + "] failed", ex);
}
List<Constructor<?>> candidates = new ArrayList<>(rawCandidates.length);
//@Autowired注解并且属性required为true 修饰的构造参数
Constructor<?> requiredConstructor = null;
//默认构造参数
Constructor<?> defaultConstructor = null;
//看了下只有koltin才会有这个primaryConstrutor
Constructor<?> primaryConstructor = BeanUtils.findPrimaryConstructor(beanClass);
int nonSyntheticConstructors = 0;
//3.2 遍历所有构造器rawCandidates，将添加@Autowired的注解添加至candidates，将无参构造赋给defaultConstructor
for (Constructor<?> candidate : rawCandidates) {
if (!candidate.isSynthetic()) {
nonSyntheticConstructors++;
}
else if (primaryConstructor != null) {
continue;
}
//判段当前构造器有没有autowired注解，没有的话去父类找找看看有没有参数一样的构造方法它有没有autowired注解
AnnotationAttributes ann = findAutowiredAnnotation(candidate);
if (ann == null) {
Class<?> userClass = ClassUtils.getUserClass(beanClass);
if (userClass != beanClass) {
try {
Constructor<?> superCtor =
userClass.getDeclaredConstructor(candidate.getParameterTypes());
ann = findAutowiredAnnotation(superCtor);
}
catch (NoSuchMethodException ex) {
// Simply proceed, no equivalent superclass constructor found...
}
}
}
if (ann != null) {
if (requiredConstructor != null) {
throw new BeanCreationException(beanName,
"Invalid autowire-marked constructor: " + candidate +
". Found constructor with 'required' Autowired annotation already: " +
requiredConstructor);
}
//判断autowired的reqired属性值(默认为true)，如果candidates中已经有构造参数，抛出异常
boolean required = determineRequiredStatus(ann);
if (required) {
if (!candidates.isEmpty()) {
throw new BeanCreationException(beanName,
"Invalid autowire-marked constructors: " + candidates +
". Found constructor with 'required' Autowired annotation: " +
candidate);
}
requiredConstructor = candidate;
}
//所有带有autowired注解的都加入candidates
candidates.add(candidate);
}
else if (candidate.getParameterCount() == 0) {
defaultConstructor = candidate;
}
}
//candidates不为空（有required为false的构造方法），并且没有required为true的构造方法，才会往candidates加默认构造方法
if (!candidates.isEmpty()) {
// Add default constructor to list of optional constructors, as fallback.
if (requiredConstructor == null) {
if (defaultConstructor != null) {
candidates.add(defaultConstructor);
}
else if (candidates.size() == 1 && logger.isInfoEnabled()) {
logger.info("Inconsistent constructor declaration on bean with name '" + beanName +
"': single autowire-marked constructor flagged as optional - " +
"this constructor is effectively required since there is no " +
"default constructor to fall back to: " + candidates.get(0));
}
}
candidateConstructors = candidates.toArray(new Constructor<?>[0]);
}
//candidates为空，但是当前类只有一个有参数构造参数，放入候选集合中
else if (rawCandidates.length == 1 && rawCandidates[0].getParameterCount() > 0) {
candidateConstructors = new Constructor<?>[] {rawCandidates[0]};
}
else if (nonSyntheticConstructors == 2 && primaryConstructor != null &&
defaultConstructor != null && !primaryConstructor.equals(defaultConstructor)) {
candidateConstructors = new Constructor<?>[] {primaryConstructor, defaultConstructor};
}
else if (nonSyntheticConstructors == 1 && primaryConstructor != null) {
candidateConstructors = new Constructor<?>[] {primaryConstructor};
}
else {
candidateConstructors = new Constructor<?>[0];
}
this.candidateConstructorsCache.put(beanClass, candidateConstructors);
}
}
}
return (candidateConstructors.length > 0 ? candidateConstructors : null);
}
2.根据推断构造参数结果实例化对象
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor
protected BeanWrapper autowireConstructor(
String beanName, RootBeanDefinition mbd, @Nullable Constructor<?>[] ctors, @Nullable Object[] explicitArgs) {
return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
}
org.springframework.beans.factory.support.ConstructorResolver
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;
}
}
}
if (argsToResolve != null) {
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;
}
}
// 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();
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) {
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;
}
if (paramTypes.length < minNrOfArgs) {
continue;
}
ArgumentsHolder argsHolder;
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);
}
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);
}
/**如果本次计算到的差异值比上一次获取到的差异值小,那么就需要做这几件事:
* 1、设置constructorToUse为当前的这个构造器
* 2、设置参数和参数值
* 3、给差异值赋值为当前计算出来的差异值
* 4、清空有歧义的集合(因为此时我们已经得到了更合适的构造器,所以有歧义的构造器里面保存的构造器已经没有存在的意义了)*/
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;
}
/**
* 如果已经找到过一次构造器,并且当前的差异值和上一次的差异值一致的话,那么说明这两个构造器是有歧义的,
* 那么就将这两个构造器放到[有歧义的构造器]集合中去.
* */
else if (constructorToUse != null && typeDiffWeight == minTypeDiffWeight) {
if (ambiguousConstructors == null) {
ambiguousConstructors = new LinkedHashSet<>();
ambiguousConstructors.add(constructorToUse);
}
ambiguousConstructors.add(candidate);
}
}
/**
* 到达这里的时候,如果还没有找到合适的构造器,那么则直接抛出异常,这个类没法实例化
* */
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)");
}
/**
* 如果存在歧义的构造器集合不为空,并且当前BeanDefinition为严格模式,那么则抛出异常,只有当BeanDefinition为宽松模式时,这种情况才不会抛异常
* */
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);
}
/**
* 如果当前getBean没有传参数,那么则将当前的构造器和参数放到缓存里面去,可能Spring认为传入参数的情况下说不准我们准备怎么做,所以干脆我们自己传入参数的就不缓存了
* */
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;
}