SpringFactoriesLoader

示例位置 SpringApplication#getSpringFactoriesInstances
加载spring.factroies下的初始化类

 ClassLoader classLoader = this.getClassLoader();
        Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
        List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
        AnnotationAwareOrderComparator.sort(instances);
        return instances;

说明：
SpringFactoriesLoader.loadFactoryNames 加载type为spring.factroies 下的 class的key值

List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader)

ClassUtils .BeanUtils

示例位置 SpringApplication#createSpringFactoriesInstances

  try {
                Class<?> instanceClass = ClassUtils.forName(name, classLoader);
                Assert.isAssignable(type, instanceClass);
                Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
                T instance = BeanUtils.instantiateClass(constructor, args);
                instances.add(instance);
            } catch (Throwable var12) {
                throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, var12);
            }

ClassUtils.forName，name为加载类的全路径名称，通过ClassUtils.forName加载对应的类
通过 instanceClass.getDeclaredConstructor(parameterTypes); 表示传入无参的构造参数
示例此处的值为：new Class[0] ，

BeanUtils.instantiateClass(constructor, args); 通过构造函数，入参实例化一个对象

org.springframework.util.ClassUtils#forName

public static Class<?> forName(String name, @Nullable ClassLoader classLoader) throws ClassNotFoundException, LinkageError

org.springframework.beans.BeanUtils#instantiateClass

 instantiateClass(Constructor<T> ctor, Object... args) 

自定义函数入参

函数参数调用方

示例位置：SpringApplicationRunListeners#starting

 this.doWithListeners("spring.boot.application.starting", (listener) -> {
            listener.starting(bootstrapContext);
        }, (step) -> {
            if (mainApplicationClass != null) {
                step.tag("mainApplicationClass", mainApplicationClass.getName());
            }
        });

函数参数定义方

   private void doWithListeners(String stepName, Consumer<SpringApplicationRunListener> listenerAction, Consumer<StartupStep> stepAction) {
        StartupStep step = this.applicationStartup.start(stepName);
        this.listeners.forEach(listenerAction);
        if (stepAction != null) {
            stepAction.accept(step);
        }
        step.end();
    }
}

springboot 监听器扩展点混合使用

bean的生命周期和run的执行顺序

通过ApplicationContextInitializer 添加FactoryPostProcessor

主要依赖于bean的生命周期，context的加载、初始化、执行在FactoryPostProcessor扩展点之前执行，所以可以通过ApplicationContextInitializer扩展点动态添加扩展点。另一方面可以从beanFactory中拿到bean的信息和context的信息

class SharedMetadataReaderFactoryContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext>, Ordered {
    public static final String BEAN_NAME = "org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory";

    SharedMetadataReaderFactoryContextInitializer() {
    }

    public void initialize(ConfigurableApplicationContext applicationContext) {
        BeanFactoryPostProcessor postProcessor = new SharedMetadataReaderFactoryContextInitializer.CachingMetadataReaderFactoryPostProcessor(applicationContext);
        applicationContext.addBeanFactoryPostProcessor(postProcessor);
    }
    ……
}

CachingMetadataReaderFactoryPostProcessor实现了BeanDefinitionRegistryPostProcessor接口，而BeanDefinitionRegistryPostProcessor接口又继承了BeanFactoryPostProcessor所以BeanDefinitionRegistryPostProcessor本身就是一个BeanFactory后置处理器

  static class CachingMetadataReaderFactoryPostProcessor implements BeanDefinitionRegistryPostProcessor, PriorityOrdered {
        private final ConfigurableApplicationContext context;

        CachingMetadataReaderFactoryPostProcessor(ConfigurableApplicationContext context) {
            this.context = context;
        }

        public int getOrder() {
            return -2147483648;
        }

        public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        }
}

利用同样的思路可以添加动态的ApplicationListenter等