spring DI 过程
...大约 16 分钟
spring DI 过程
SpringBoot版本：spring-context-5.2.8.RELEASE.jar SpringBoot版本：spring-context-5.2.8.RELEASE.jar SpringBoot版本：spring-context-5.2.8.RELEASE.jar
0. 依赖注入
构造函数注入
package x.y;
public class ThingOne {
private String name;
private int age;
private BelongToFirst sex;
public ConstructorBean1(String name, int age,BelongToFirst sex) {
this.name = name;
this.age = age;
this.sex = sex;
}
}
假设ThingTwo和ThingThree类不通过继承相关，则不存在潜在的歧义。因此，以下配置工作正常，您无需在 <constructor-arg/>元素中显式指定构造函数参数索引或类型。
<beans>
<bean id="constructorBean1" class="learn.note.springlearn.bean.userxmlbean.ConstructorBean1">
<constructor-arg value="wangwenlei"></constructor-arg>
<constructor-arg value="25"></constructor-arg>
<constructor-arg ref="belongToFirst"></constructor-arg>
</bean>
<bean id="belongToFirst" class="learn.note.springlearn.bean.userxmlbean.BelongToFirst">
<property name="sex" value="男"></property>
</bean>
</beans>
也可以使用索引或使用name：
<beans> <bean id="constructorBean1" class="learn.note.springlearn.bean.userxmlbean.ConstructorBean1"> <constructor-arg index="0" value="wangwenlei"></constructor-arg> <constructor-arg name="age" value="25"></constructor-arg> <constructor-arg index="2" ref="belongToFirst"></constructor-arg> </bean> <bean id="belongToFirst" class="learn.note.springlearn.bean.userxmlbean.BelongToFirst"> <property name="sex" value="男"></property> </bean> </beans>
setter注入
public class BelongToFirst {
private String sex;
public void setSex(String sex) {
this.sex = sex;
}
}
xml配置
<beans>
<bean id="belongToFirst" class="learn.note.springlearn.bean.userxmlbean.BelongToFirst">
<property name="sex" value="男"></property>
</bean>
</beans>
在命名空间上添加 xmlns:p="http://www.springframework.org/schema/p" 就可以使用更简洁的 XML 配置：
<beans>
<bean id="belongToFirst" class="learn.note.springlearn.bean.userxmlbean.BelongToFirst"
p:sex="男"
/>
</beans>
使用初体验
public class Main {
public static void main(String[] args) {
// 你的配置文件名，放在根路径resources下
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("service-learn.xml");
// 使用getBean方法可以检索bean的实例
final ConstructorBean1 firstXml = context.getBean("constructorBean1", ConstructorBean1.class);
// 因为已经配置了值，取出后直接使用
System.out.println(firstXml.getName());
System.out.println(firstXml.getAge());
// 试下对象里依赖另一个Bean
System.out.println(firstXml.getSex());
}
}
发生的时间
依赖注入有两种情况触发
- 用户第一次调用getBean()方法时，IoC容器触发依赖注入
- 当属性设为懒加载时，容器在解析注册Bean定义时进行预实例化
1. 寻找getBean()的入口
BeanFactory接口定义了SpringIoC容器的基本功能规范。BeanFactory接口中定义了几个getBean()方法，用于用户向IoC容器索取被管理的Bean的方法。 BeanFactory是接口，具体情况看他的实现AbstractBeanFactory，类图如下：
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
@Override
public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
return doGetBean(name, requiredType, null, false);
}
@Override
public Object getBean(String name, Object... args) throws BeansException {
return doGetBean(name, null, args, false);
}
/**
* Return an instance, which may be shared or independent, of the specified bean.
* 返回指定 bean 的一个实例，该实例可以是共享的，也可以是独立的。
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
public <T> T getBean(String name, @Nullable Class<T> requiredType, @Nullable Object... args)
throws BeansException {
return doGetBean(name, requiredType, args, false);
}
2.整体调用逻辑
干活的都do开头的，看下doGetBean
/**
* Return an instance, which may be shared or independent, of the specified bean.
* 返回一个实例，它可以与指定的 bean 共享或独立
* @param name 要检索的 bean 的名称
* @param requiredType 要检索的 bean 的所需类型
* @param args 使用显式参数创建 bean 实例时使用的参数
* (仅在创建新实例而不是检索现有实例时应用)
* @param typeCheckOnly 是否获取实例用于类型检查，不用于实际使用
* @return bean 的一个实例
* @throws BeansException 如果无法创建 bean
*/
@SuppressWarnings("unchecked")
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
// 返回 bean 名称，必要时去除工厂取消引用前缀，并将别名解析为规范名称
String beanName = transformedBeanName(name);
Object bean;
// 从缓存中读取是否已经有被创建的单例模式的Bean
Object sharedInstance = getSingleton(beanName);
// 如果从手动注册的单例singletonObjects或earlySingletonObjects Map中找到
if (sharedInstance != null && args == null) {
if (logger.isTraceEnabled()) {
// 在整个工厂内单例 bean 当前是否正在创建中
if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
"' that is not fully initialized yet - a consequence of a circular reference");
}
else {
logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
}
}
// 获取 Bean 实例的对象。主要完成FactoryBean的相关处理。
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// 原型 bean 当前前线程是否正在创建中（缓存中已经有原型模式的Bean)
// 如果我们已经在创建这个 bean 实例，则失败： 我们可能在循环引用中
if (isPrototypeCurrentlyInCreation(beanName)) {
// 是在创建中则抛出Exception
throw new BeanCurrentlyInCreationException(beanName);
}
// 检查此工厂中是否存在 bean 定义。
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
// 没有发现 则 检查其父
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {
return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
// 根据指定Bean名称获取其父级Bean定义，主要解决Bean继承时子类和父类公共属性问题
RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
// 获取当前Bean所有依赖Bean的名称
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
// 把被依赖Bean注册给当前依赖的Bean
registerDependentBean(dep, beanName);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
// Create bean instance.
// 创建一个单例模式的Bean的实例对象
if (mbd.isSingleton()) {
// 创建实例对象并注册给所依赖的对象
sharedInstance = getSingleton(beanName, () -> {
try {
// 回调实现创建Bean实例对象
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
// 获取给定Bean的实例对象
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
// IoC容器创建原型模式的Bean的实例对象
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
// 创建的Bean既不是单例的也不是原型模式的
// 根据Bean定义资源中配置的方式
String scopeName = mbd.getScope();
if (!StringUtils.hasLength(scopeName)) {
throw new IllegalStateException("No scope name defined for bean ´" + beanName + "'");
}
Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope '" + scopeName + "' is not active for the current thread; consider " +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {
cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// 检查所需类型是否与实际 bean 实例的类型匹配。
if (requiredType != null && !requiredType.isInstance(bean)) {
try {
T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean '" + name + "' to required type '" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
上面源码只定义了根据Bean定义的不同采取不同策略创建Bean实例，具体的Bean实例对象的创建过程是有实现了ObjectFactory接口的creatBean()方法完成。 具体实现类SpringBoot这里由其实现类AbstractAutowireCapableBeanFactory完成。看下源码：
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isTraceEnabled()) {
logger.trace("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
// mbd是否有BeanClass
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// 准备方法覆盖。
try {
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
// 让 BeanPostProcessors 有机会返回一个代理而不是目标 bean 实例。
// (如果Bean配置了初始化前和初始化后的处理器，则试图返回一个需要创建Bean的代理对象)
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
// 创建Bean的入口
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isTraceEnabled()) {
logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
2.1真正创建Bean的方法
// 真正创建Bean的方法
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// 实例化Bean
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
// 是单例的话，从工厂 Bean 实例缓存移出这个beanName
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 没得到的话，用适当的实例化策略为指定的 bean 创建一个新实例： 工厂方法、构造函数自动装配或简单实例化。
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
// 获取实例化的类型
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
// 允许后处理器修改合并的 bean 定义。
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// 调用PostProcess后置处理器-增强器
// 将 MergedBeanDefinitionPostProcessors 应用于指定的 bean 定义，调用它们的 postProcessMergedBeanDefinition 方法。
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
// 向容器缓存中缓存单例模式的Bean对象，以防止循环引用
// 是单例的 是支持循环引用的 是正在初始化的 则为 true
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");
}
// 这里会添加一个回调 给到 singletonFactories。尽早持有引用
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
// Bean的初始化，》》》》》》》》》》》》》》》********** 依赖注入在此触发 *******《《《《《《《《《《《《《《《
Object exposedObject = bean;
try {
// 将Bean实例对象封装，并且将Bean定义中的配置的属性值赋值给实例对象。
// 这里会把所有的InstantiationAwareBeanPostProcessor都触发，肯定包括AutowiredAnnotationBeanPostProcessor啦
populateBean(beanName, mbd, instanceWrapper);
// 初始化Bean对象
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);
}
}
if (earlySingletonExposure) {
Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
/**
* Create a new instance for the specified bean, using an appropriate instantiation strategy:
* factory method, constructor autowiring, or simple instantiation.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a BeanWrapper for the new instance
* @see #obtainFromSupplier
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
* @see #instantiateBean
*/
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
// 确认Bean是可实例化的
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());
}
// 返回用于创建 bean 实例的回调（如果有）。
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
// 从给定的提供者处获取一个 bean 实例
return obtainFromSupplier(instanceSupplier, beanName);
}
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
// 重新创建相同 bean 时的快捷方式
// 是否需要解决自动装配化的变量 默认否
boolean resolved = false;
// 自动装配化 必要？
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
// 配置了自动装配属性，使用容器的自动装配进行实例化
// 容器的自动装配根据参数类型匹配Bean的构造方法
return autowireConstructor(beanName, mbd, null, null);
}
else {
// 使用默认的无参构造方法进行实例化
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
// 使用Bean的构造方法进行实例化
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
// 使用容器的自动装配特性，调用匹配的构造方法进行实例化
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
// 默认构造的首选构造函数？
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
// 使用默认的无参构造方法进行实例化
return instantiateBean(beanName, mbd);
}
// 默认的无参构造方法进行实例化
protected BeanWrapper instantiateBean(String beanName, RootBeanDefinition mbd) {
try {
Object beanInstance;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged(
(PrivilegedAction<Object>) () -> getInstantiationStrategy().instantiate(mbd, beanName, this),
getAccessControlContext());
}
else {
// 通过实例化策略实例化
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, this);
}
// 把实例化的对象包装成 BeanWrapper 对象
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}
2.2执行Bean的实例化
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
// 如果没有覆盖，请不要使用 CGLIB 覆盖该类。
if (!bd.hasMethodOverrides()) {
Constructor<?> constructorToUse;
synchronized (bd.constructorArgumentLock) {
// 获取对象的构造方法或工厂方法
constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
// 没有构造方法或工厂方法进入判断
if (constructorToUse == null) {
// JDK反射机制，到要实例化的类
final Class<?> clazz = bd.getBeanClass();
// 判断是否是接口
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
// 安全管理器不为空
if (System.getSecurityManager() != null) {
// 回调方法，得到Bean的构造方法
constructorToUse = AccessController.doPrivileged(
(PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
}
else {
// 直接得到Bean的构造方法
constructorToUse = clazz.getDeclaredConstructor();
}
// 给RootBeanDefinition 存储构造方法和工厂方法变量 赋值
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// Must generate CGLIB subclass.
// 必须生成 CGLIB 子类，这里点进去直接是一个抛出异常的方法，都是他的子类可以重写此方法。下面看重写详情
return instantiateWithMethodInjection(bd, beanName, owner);
}
}
2.2.1JDK 反射实例Class
public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
ReflectionUtils.makeAccessible(ctor);
// 确定是否存在 Kotlin 反射 且 是否是 Kotlin 类型
if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {
// Kotlin方式实例化
return KotlinDelegate.instantiateClass(ctor, args);
}
else {
// 获取构造方法参数类型数组
Class<?>[] parameterTypes = ctor.getParameterTypes();
Assert.isTrue(args.length <= parameterTypes.length, "Can't specify more arguments than constructor parameters");
Object[] argsWithDefaultValues = new Object[args.length];
// 处理参数
for (int i = 0 ; i < args.length; i++) {
// 构造函数对应位置上的参数未传入
if (args[i] == null) {
Class<?> parameterType = parameterTypes[i];
// 根据是基本类型，初始化一个基本类型或null
argsWithDefaultValues[i] = (parameterType.isPrimitive() ? DEFAULT_TYPE_VALUES.get(parameterType) : null);
}
else {
// 传入的话赋值到参数数组
argsWithDefaultValues[i] = args[i];
}
}
// 》》》》》 *** 终于真正的最终的执行实例化 *** 《《《《
return ctor.newInstance(argsWithDefaultValues);
}
}
catch (InstantiationException ex) {
throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {
throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
}
}
2.2.1 CGLib 反射实例Class
@Override
protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// 调用下面方法
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...
// 下面看instantiate详情
return new CglibSubclassCreator(bd, owner).instantiate(ctor, args);
}
public Object instantiate(@Nullable Constructor<?> ctor, Object... args) {
// 使用 CGLIB 为提供的 bean 定义创建 bean 类的增强子类。
Class<?> subclass = createEnhancedSubclass(this.beanDefinition);
Object instance;
if (ctor == null) {
// 无参构造
instance = BeanUtils.instantiateClass(subclass);
}
else {
// 有参构造
try {
Constructor<?> enhancedSubclassConstructor = subclass.getConstructor(ctor.getParameterTypes());
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.
// SPR-10785：直接在实例上设置回调，而不是在增强类（通过增强器）以避免内存泄漏。
Factory factory = (Factory) instance;
factory.setCallbacks(new Callback[] {NoOp.INSTANCE,
new LookupOverrideMethodInterceptor(this.beanDefinition, this.owner),
new ReplaceOverrideMethodInterceptor(this.beanDefinition, this.owner)});
return instance;
}
2.3 填充属性
下面原码之前先来了解下Spring之InstantiationAwareBeanPostProcessor接口，不然看的会有点懵。
Spring之InstantiationAwareBeanPostProcessor接口，介绍对象创建过程中用到的几个回调方法
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
if (bw == null) {
if (mbd.hasPropertyValues()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
return;
}
}
// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of the bean before properties are set. This can be used, for example,
// to support styles of field injection.
// 让任何 InstantiationAwareBeanPostProcessors 有机会在设置属性之前修改 bean 的状态。
// 例如，这可以用于支持字段注入的样式。
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
//postProcessAfterInstantiation 这个方法返回true，后面的处理器才会继续执行，但返回false，直接return了
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
// 处理器若告知说不用继续赋值了，那就以处理器的结果为准即可
return;
}
}
}
}
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
// 调用 postProcessProperties方法
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
// 如果返回null,调用 postProcessPropertyValues 方法。感觉这里编写目的是兼容已废弃方法
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
}
if (needsDepCheck) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
// 真正设置属性的方法。
if (pvs != null) {
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
2.4 初始化Bean对象
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
// 通过JDK的安全机制验证权限
if (System.getSecurityManager() != null) {
// 实现 PrivilegedAction 接口的匿名内部类
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
// 为Bean实例对象包装相关属性，如名称、类加载器、所属容器等
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 调用 BeanPostProcessor 后置处理器的回调方法，在Bean实例初始化前做一些事情
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 调用Bean实例化方法，这个初始化方法是在Spring Bean定义配置文件中通过init-Method属性指定的
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
// 调用 BeanPostProcessor 后置处理器的回调方法，在Bean实例初始化后做一些事情
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
3.寻找使用getBean()的入口
3.1 SpringBoot启动时触发加载Bean
refresh()方法中registerBeanPostProcessors(beanFactory);
3.2 @Autowire注解
- 任何 InstantiationAwareBeanPostProcessors 有机会在设置属性之前修改 bean 的状态
- 任何 InstantiationAwareBeanPostProcessors 给Bean设置属性
扩展会所有的BeanPostProcessors，其中就包括AutowiredAnnotationBeanPostProcessor。 postProcessProperties()处理面有一步descriptor.getResolvableType()方法使用了getBean()。细节:@Autowire具体如何获取到对象
拓展
<bean id="mappings"
class="org.springframework.context.support.PropertySourcesPlaceholderConfigurer">
<!-- typed as a java.util.Properties -->
<property name="properties">
<value>
jdbc.driver.className=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mydb
</value>
</property>
</bean>
Spring 容器通过使用 JavaBeans机制将<value/>元素内的文本转换为 实例。这是一个不错的捷径，也是 Spring 团队支持使用嵌套元素而不是属性样式的少数几个地方之一。java.util.PropertiesPropertyEditor的<value/>value