public interface InstantiationStrategy {/*** 默认构造方法*/Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner)throws BeansException;/*** 指定构造方法*/Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,Constructor<?> ctor, @Nullable Object... args) throws BeansException;/*** 工厂方法*/Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,@Nullable Object factoryBean, Method factoryMethod, @Nullable Object... args)throws BeansException;}

// SimpleInstantiationStrategy.java@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,@Nullable Object factoryBean, final Method factoryMethod, Object... args) {try {// 设置 Method 可访问if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {ReflectionUtils.makeAccessible(factoryMethod);return null;});} else {ReflectionUtils.makeAccessible(factoryMethod);}// 获得原 Method 对象Method priorInvokedFactoryMethod = currentlyInvokedFactoryMethod.get();try {// 设置新的 Method 对象，到 currentlyInvokedFactoryMethod 中currentlyInvokedFactoryMethod.set(factoryMethod);// 创建 Bean 对象Object result = factoryMethod.invoke(factoryBean, args);// 未创建，则创建 NullBean 对象if (result == null) {result = new NullBean();}return result;} finally {// 设置老的 Method 对象，到 currentlyInvokedFactoryMethod 中if (priorInvokedFactoryMethod != null) {currentlyInvokedFactoryMethod.set(priorInvokedFactoryMethod);} else {currentlyInvokedFactoryMethod.remove();}}// 一大堆 catch 异常} 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());}
}

// SimpleInstantiationStrategy.java// 默认构造方法
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {// Don't override the class with CGLIB if no overrides.// 没有覆盖，直接使用反射实例化即可if (!bd.hasMethodOverrides()) {Constructor<?> constructorToUse;synchronized (bd.constructorArgumentLock) {// 获得构造方法 constructorToUseconstructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;if (constructorToUse == null) {final Class<?> clazz = bd.getBeanClass();// 如果是接口，抛出 BeanInstantiationException 异常if (clazz.isInterface()) {throw new BeanInstantiationException(clazz, "Specified class is an interface");}try {// 从 clazz 中，获得构造方法if (System.getSecurityManager() != null) { // 安全模式constructorToUse = AccessController.doPrivileged((PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);} else {constructorToUse =	clazz.getDeclaredConstructor();}// 标记 resolvedConstructorOrFactoryMethod 属性bd.resolvedConstructorOrFactoryMethod = constructorToUse;} catch (Throwable ex) {throw new BeanInstantiationException(clazz, "No default constructor found", ex);}}}// 通过 BeanUtils 直接使用构造器对象实例化 Bean 对象return BeanUtils.instantiateClass(constructorToUse);} else {// Must generate CGLIB subclass.// 生成 CGLIB 创建的子类对象return instantiateWithMethodInjection(bd, beanName, owner);}
}// 指定构造方法
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner,final Constructor<?> ctor, Object... args) {// 没有覆盖，直接使用反射实例化即可if (!bd.hasMethodOverrides()) {if (System.getSecurityManager() != null) {// 设置构造方法，可访问// use own privileged to change accessibility (when security is on)AccessController.doPrivileged((PrivilegedAction<Object>) () -> {ReflectionUtils.makeAccessible(ctor);return null;});}// 通过 BeanUtils 直接使用构造器对象实例化 Bean 对象return BeanUtils.instantiateClass(ctor, args);} else {// 生成 CGLIB 创建的子类对象return instantiateWithMethodInjection(bd, beanName, owner, ctor, args);}
}

// SimpleInstantiationStrategy.javaprotected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {throw new UnsupportedOperationException("Method Injection not supported in SimpleInstantiationStrategy");
}// CglibSubclassingInstantiationStrategy.java@Override
protected Object instantiateWithMethodInjection(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {return instantiateWithMethodInjection(bd, beanName, owner, null);
}

// CglibSubclassingInstantiationStrategy.java#CglibSubclassCreatorenhancer.setCallbackFilter(new MethodOverrideCallbackFilter(beanDefinition));
enhancer.setCallbackTypes(CALLBACK_TYPES);

// CglibSubclassingInstantiationStrategy.java#MethodOverrideCallbackFilter@Override
public int accept(Method method) {MethodOverride methodOverride = getBeanDefinition().getMethodOverrides().getOverride(method);if (logger.isTraceEnabled()) {logger.trace("Override for '" + method.getName() + "' is [" + methodOverride + "]");}if (methodOverride == null) {return PASSTHROUGH;} else if (methodOverride instanceof LookupOverride) {return LOOKUP_OVERRIDE;} else if (methodOverride instanceof ReplaceOverride) {return METHOD_REPLACER;}throw new UnsupportedOperationException("Unexpected MethodOverride subclass: " +methodOverride.getClass().getName());
}

// CglibSubclassingInstantiationStrategy.java#LookupOverrideMethodInterceptorprivate static class LookupOverrideMethodInterceptor extends CglibIdentitySupport implements MethodInterceptor {private final BeanFactory owner;public LookupOverrideMethodInterceptor(RootBeanDefinition beanDefinition, BeanFactory owner) {super(beanDefinition);this.owner = owner;}@Overridepublic Object intercept(Object obj, Method method, Object[] args, MethodProxy mp) throws Throwable {// Cast is safe, as CallbackFilter filters are used selectively.// 获得 method 对应的 LookupOverride 对象LookupOverride lo = (LookupOverride) getBeanDefinition().getMethodOverrides().getOverride(method);Assert.state(lo != null, "LookupOverride not found");// 获得参数Object[] argsToUse = (args.length > 0 ? args : null);  // if no-arg, don't insist on args at all// 获得 Beanif (StringUtils.hasText(lo.getBeanName())) { // Bean 的名字return (argsToUse != null ? this.owner.getBean(lo.getBeanName(), argsToUse) :this.owner.getBean(lo.getBeanName()));} else { // Bean 的类型return (argsToUse != null ? this.owner.getBean(method.getReturnType(), argsToUse) :this.owner.getBean(method.getReturnType()));}}
}

// CglibSubclassingInstantiationStrategy.java#ReplaceOverrideMethodInterceptorprivate static class ReplaceOverrideMethodInterceptor extends CglibIdentitySupport implements MethodInterceptor {private final BeanFactory owner;public ReplaceOverrideMethodInterceptor(RootBeanDefinition beanDefinition, BeanFactory owner) {super(beanDefinition);this.owner = owner;}@Overridepublic Object intercept(Object obj, Method method, Object[] args, MethodProxy mp) throws Throwable {// 获得 method 对应的 LookupOverride 对象ReplaceOverride ro = (ReplaceOverride) getBeanDefinition().getMethodOverrides().getOverride(method);Assert.state(ro != null, "ReplaceOverride not found");// TODO could cache if a singleton for minor performance optimization// 获得 MethodReplacer 对象MethodReplacer mr = this.owner.getBean(ro.getMethodReplacerBeanName(), MethodReplacer.class);// 执行替换return mr.reimplement(obj, method, args);}
}