1.3、解析并创建ApplicationListener（ok）-CFANZ编程社区

1、流程概述

1、从classpath下的 META-INF/spring.factories（点击查看）文件中找出 ApplicationListener 类型的所有类的全类名。

2、通过反射创建这些类的对象

3、最后把这些对象放入SpringApplication对象的List实例变量中。

示意图

2、状态图

此时 SpringApplication 对象的内存状态如下图

SpringApplication 内存状态

3、源码解读

2.1、源码结构

源码结构:

initialize

|- getSpringFactoriesInstances

|- SpringFactoriesLoader.loadFactoryNames

|- createSpringFactoriesInstances

|- AnnotationAwareOrderComparator.sort

|- setListeners

2.2、参考源码

private void initialize(Object[] sources) {
  if (sources != null && sources.length > 0) {
    this.sources.addAll(Arrays.asList(sources));
  }
  this.webEnvironment = deduceWebEnvironment();
  setInitializers((Collection) getSpringFactoriesInstances(
      ApplicationContextInitializer.class));
  setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
  this.mainApplicationClass = deduceMainApplicationClass();
}

本文关注的是这行代码：setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class))

private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
  return getSpringFactoriesInstances(type, new Class<?>[] {});
}

private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
    Class<?>[] parameterTypes, Object... args) {
  ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
  // Use names and ensure unique to protect against duplicates
  Set<String> names = new LinkedHashSet<String>(
      SpringFactoriesLoader.loadFactoryNames(type, classLoader));
  List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
      classLoader, args, names);
  AnnotationAwareOrderComparator.sort(instances);
  return instances;
}
private List<ApplicationListener<?>> listeners;
public void setListeners(Collection<? extends ApplicationListener<?>> listeners) {
  this.listeners = new ArrayList<ApplicationListener<?>>();
  this.listeners.addAll(listeners);
}

getSpringFactoriesInstances方法用来解析并创建 ApplicationListener 实例
其中 getSpringFactoriesInstances(ApplicationListener.class) 如下：

names = {LinkedHashSet@1636}  size = 10
 0 = "o.s.boot.ClearCachesApplicationListener"
 1 = "o.s.boot.builder.ParentContextCloserApplicationListener"
 2 = "o.s.boot.context.FileEncodingApplicationListener"
 3 = "o.s.boot.context.config.AnsiOutputApplicationListener"
 4 = "o.s.boot.context.config.ConfigFileApplicationListener"
 5 = "o.s.boot.context.config.DelegatingApplicationListener"
 6 = "o.s.boot.liquibase.LiquibaseServiceLocatorApplicationListener"
 7 = "o.s.boot.logging.ClasspathLoggingApplicationListener"
 8 = "o.s.boot.logging.LoggingApplicationListener"
 9 = "o.s.boot.autoconfigure.BackgroundPreinitializer"

setListeners方法这些实例放入SpringApplication 实例的 List<ApplicationListener<?>> listeners 变量中。

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