Spring 核心方法 refresh 刷新流程简要概述及相关源码扩展实现（一）（上）

// 创建 Ant【表达式语言】 方式的路径匹配器
private PathMatcher pathMatcher = new AntPathMatcher();

protected void customizePropertySources(MutablePropertySources propertySources) {
    propertySources.addLast(new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME,getSystemProperties()));
    propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,getSystemEnvironment()));
}

protected void prepareRefresh() {
    // 设置容器启动的时间
    this.startupDate = System.currentTimeMillis();
    // 容器的关闭标志位
    this.closed.set(false);
    // 容器的激活标志位
    this.active.set(true);
    // 记录日志
    if (logger.isDebugEnabled()) {
      if (logger.isTraceEnabled()) {
        logger.trace("Refreshing " + this);
      }
      else {
        logger.debug("Refreshing " + getDisplayName());
      }
    }
    // Initialize any placeholder property sources in the context environment.
    // 留给子类覆盖扩展，初始化属性资源，钩子函数
    initPropertySources();
    // Validate that all properties marked as required are resolvable:
    // see ConfigurablePropertyResolver#setRequiredProperties
    // 创建并获取环境对象，验证需要的属性文件是否都已经放入环境中，如果没有放入就抛出异常
    getEnvironment().validateRequiredProperties();
    // Store pre-refresh ApplicationListeners...
    // 判断刷新前的应用程序监听器集合是否为空，如果为空，则将监听器添加到此集合中
    if (this.earlyApplicationListeners == null) {
      this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
    }
    else {
      // Reset local application listeners to pre-refresh state.
      // 如果不等于空，则清空集合元素对象
      this.applicationListeners.clear();
      this.applicationListeners.addAll(this.earlyApplicationListeners);
    }
    // Allow for the collection of early ApplicationEvents,
    // to be published once the multicaster is available...
    // 创建刷新前的监听事件集合
    this.earlyApplicationEvents = new LinkedHashSet<>();
  }

public class MyClassPathXmlApplicationContext extends ClassPathXmlApplicationContext {
    public MyClassPathXmlApplicationContext(String... configLocations){
        super(configLocations);
    }
    @Override
    protected void initPropertySources() {
        System.out.println("扩展initPropertySource");
        // 若系统属性中不存在 username，会抛出异常.
        getEnvironment().setRequiredProperties("username");
    }
}

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
  // 初始化 BeanFactory，并进行 XML 文件读取，并将得到的 BeanFactory 记录在当前实体的属性中
  refreshBeanFactory();
  // 返回当前实体 beanFactory 属性
  return getBeanFactory();
}

@Override
protected final void refreshBeanFactory() throws BeansException {
  // 如果存在beanFactory，则销毁beanFactory
  if (hasBeanFactory()) {
    destroyBeans();
    closeBeanFactory();
  }
  try {
    // 创建DefaultListableBeanFactory对象
    DefaultListableBeanFactory beanFactory = createBeanFactory();
    // 为了序列化指定id，可以从id反序列化到beanFactory对象
    beanFactory.setSerializationId(getId());
    // 定制beanFactory，设置相关属性，包括是否允许覆盖同名称的不同定义的对象以及循环依赖
    customizeBeanFactory(beanFactory);
    // 初始化documentReader,并进行XML文件读取及解析,默认命名空间的解析，自定义标签的解析
    loadBeanDefinitions(beanFactory);
    this.beanFactory = beanFactory;
  }
  catch (IOException ex) {
    throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
  }
}

protected final void refreshBeanFactory() throws IllegalStateException {
  if (!this.refreshed.compareAndSet(false, true)) {
    throw new IllegalStateException(
        "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
  }
  this.beanFactory.setSerializationId(getId());
}

protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            switch(this.webApplicationType) {
            case SERVLET:
                contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
                break;
            case REACTIVE:
                contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
                break;
            default:
                contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
            }
        } catch (ClassNotFoundException var3) {
            throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
        }
    }
    return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
}

public AbstractAutowireCapableBeanFactory() {
  super();
  // 忽略要依赖的接口
  ignoreDependencyInterface(BeanNameAware.class);
  ignoreDependencyInterface(BeanFactoryAware.class);
  ignoreDependencyInterface(BeanClassLoaderAware.class);
}

// 此方法可以交由子类去自由扩展实现
@Override
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
  super.setAllowBeanDefinitionOverriding(false);
  super.setAllowCircularReferences(false);
  super.customizeBeanFactory(beanFactory);
}

this.dtdResolver = new BeansDtdResolver();
// 当完成这行代码的调用之后，大家神奇的发现一件事情，schemaResolver 对象的 schemaMappings 属性被完成了赋值操作，但是你遍历完成所有代码后依然没有看到显式调用
// 其实此时的原理是非常简单的，我们在进行 debug 的时候，因为在程序运行期间需要显示当前类的所有信息，所以 idea 会帮助我们调用 toString 方法，只不过此过程我们识别不到而已，idea 中可以设置关闭 Debug 模式下 toString 方法调用
// toString(){return "EntityResolver using schema mappings " + getSchemaMappings();}
// 会去加载 META-INF/spring.schemas 文件下所有键值对
this.schemaResolver = new PluggableSchemaResolver(classLoader);