一直在用的 Spring，你知道它的加载原理吗？

package com.wokao666;
public class Student {
  private int id;  private String name;  private int age;
  public int getId() {    return id;  }
  public void setId(int id) {    this.id = id;  }
  public String getName() {    return name;  }
  public void setName(String name) {    this.name = name;  }
  public int getAge() {    return age;  }
  public void setAge(int age) {    this.age = age;  }
  public Student(int id, String name, int age) {    super();    this.id = id;    this.name = name;    this.age = age;  }
  public Student() {    super();  }
  @Override  public String toString() {    return "Student [id=" + id + ", ]";  }
}

<bean id="stu1" class="com.wokao666.Student">   <property >property>   <property >property>   <property >property> bean>  <bean id="stu2" class="com.wokao666.Student">   <property >property>   <property >property>   <property >property> bean>

/** * Set the config locations for this application context.//未应用上下文设置资源路径 * 
If not set, the implementation may use a default as appropriate.//如果未设置，则实现可以根据需要使用默认值。 */public void setConfigLocations(String... locations) {  if (locations != null) {//非空    Assert.noNullElements(locations, "Config locations must not be null");//断言保证locations的每个元素都不为null    this.configLocations = new String[locations.length];    for (int i = 0; i < locations.length; i++) {      this.configLocations[i] = resolvePath(locations[i]).trim();//去空格，很好奇resolvePath做了什么事情？    }  }  else {    this.configLocations = null;  }}

/** * 解析给定的资源路径，必要时用相应的环境属性值替换占位符，应用于资源路径配置。 * Resolve the given path, replacing placeholders with corresponding * environment property values if necessary. Applied to config locations. * @param path the original file path * @return the resolved file path * @see org.springframework.core.env.Environment#resolveRequiredPlaceholders(String) */protected String resolvePath(String path) {  return getEnvironment().resolveRequiredPlaceholders(path);}
进入getEnvironment()看看：/** * {@inheritDoc} * 
If {@code null}, a new environment will be initialized via * {@link #createEnvironment()}. */@Overridepublic ConfigurableEnvironment getEnvironment() {  if (this.environment == null) {    this.environment = createEnvironment();  }  return this.environment;}

@Overridepublic void refresh() throws BeansException, IllegalStateException {  synchronized (this.startupShutdownMonitor) {    // 刷新前准备工作，包括设置启动时间，是否激活标识位，初始化属性源(property source)配置    prepareRefresh();
    // 创建beanFactory（过程是根据xml为每个bean生成BeanDefinition并注册到生成的beanFactory    ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    //准备创建好的beanFactory（给beanFactory设置ClassLoader，设置SpEL表达式解析器，设置类型转化器【能将xml String类型转成相应对象】，    //增加内置ApplicationContextAwareProcessor对象，忽略各种Aware对象，注册各种内置的对账对象【BeanFactory，ApplicationContext】等，    //注册AOP相关的一些东西，注册环境相关的一些bean    prepareBeanFactory(beanFactory);
    try {      // 模板方法，为容器某些子类扩展功能所用（工厂后处理器）这里可以参考BeanFactoryPostProcessor接口的postProcessBeanFactory方法      postProcessBeanFactory(beanFactory);
      // 调用所有BeanFactoryPostProcessor注册为Bean      invokeBeanFactoryPostProcessors(beanFactory);
      // 注册所有实现了BeanPostProcessor接口的Bean      registerBeanPostProcessors(beanFactory);
      // 初始化MessageSource，和国际化相关      initMessageSource();
      // 初始化容器事件传播器      initApplicationEventMulticaster();
      // 调用容器子类某些特殊Bean的初始化，模板方法      onRefresh();
      // 为事件传播器注册监听器      registerListeners();
      // 初始化所有剩余的bean（普通bean）      finishBeanFactoryInitialization(beanFactory);
      // 初始化容器的生命周期事件处理器，并发布容器的生命周期事件      finishRefresh();    }    catch (BeansException ex) {      if (logger.isWarnEnabled()) {        logger.warn("Exception encountered during context initialization - " +            "cancelling refresh attempt: " + ex);      }      // 销毁已创建的bean      destroyBeans();      // 重置`active`标志      cancelRefresh(ex);      throw ex;    }    finally {              //重置一些缓存      resetCommonCaches();    }  }}

/** * Prepare this context for refreshing, setting its startup date and * active flag as well as performing any initialization of property sources. */protected void prepareRefresh() {  this.startupDate = System.currentTimeMillis();//设置容器启动时间  this.closed.set(false);//容器关闭标志，是否关闭？  this.active.set(true);//容器激活标志，是否激活？    if (logger.isInfoEnabled()) {//运行到这里，控制台就会打印当前容器的信息    logger.info("Refreshing " + this);  }
  // 空方法，由子类覆盖实现，初始化容器上下文中的property文件  initPropertySources();
  //验证标记为必需的所有属性均可解析，请参阅ConfigurablePropertyResolver＃setRequiredProperties  getEnvironment().validateRequiredProperties();
  //允许收集早期的ApplicationEvents，一旦多播器可用，即可发布...  this.earlyApplicationEvents = new LinkedHashSet();}

三月 22, 2018 4:21:13 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@96532d6: startup date [Thu Mar 22 16:21:09 CST 2018]; root of context hierarchy

/** * 告诉子类刷新内部bean工厂(子类是指AbstractApplicationContext的子类，我们使用的是ClassPathXmlApplicationContext) * Tell the subclass to refresh the internal bean factory. */protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {  refreshBeanFactory();//刷新Bean工厂，如果已经存在Bean工厂，那就关闭并销毁，再创建一个新的bean工厂  ConfigurableListableBeanFactory beanFactory = getBeanFactory();//获取新创建的Bean工厂  if (logger.isDebugEnabled()) {    logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);//控制台打印  }  return beanFactory;}
进入refreshBeanFactory()方法：/** * 该实现执行该上下文的基础Bean工厂的实际刷新，关闭以前的Bean工厂（如果有的话）以及为该上下文的生命周期的下一阶段初始化新鲜的Bean工厂。 * This implementation performs an actual refresh of this context's underlying * bean factory, shutting down the previous bean factory (if any) and * initializing a fresh bean factory for the next phase of the context's lifecycle. */@Overrideprotected final void refreshBeanFactory() throws BeansException {  if (hasBeanFactory()) {//如果已有bean工厂    destroyBeans();//销毁    closeBeanFactory();//关闭  }  try {    DefaultListableBeanFactory beanFactory = createBeanFactory();//创建一个新的bean工厂    beanFactory.setSerializationId(getId());//为序列化目的指定一个id，如果需要，可以将此BeanFactory从此id反序列化回BeanFactory对象。    //定制容器，设置启动参数（bean可覆盖、循环引用），开启注解自动装配    customizeBeanFactory(beanFactory);    ////将所有BeanDefinition载入beanFactory中，此处依旧是模板方法，具体由子类实现    loadBeanDefinitions(beanFactory);    //beanFactory同步赋值    synchronized (this.beanFactoryMonitor) {      this.beanFactory = beanFactory;    }  }  catch (IOException ex) {    throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);  }}

/** * 使用XmlBeanDefinitionReader来加载beandefnition，之前说过使用reader机制加载Resource资源变为BeanDefinition对象 * Loads the bean definitions via an XmlBeanDefinitionReader. * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader * @see #initBeanDefinitionReader * @see #loadBeanDefinitions */@Overrideprotected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {  // 创建XmlBeanDefinitionReader对象  XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
  // 使用当前上下文Enviroment中的Resource配置beanDefinitionReader，因为beanDefinitionReader要将Resource解析成BeanDefinition嘛！  beanDefinitionReader.setEnvironment(this.getEnvironment());  beanDefinitionReader.setResourceLoader(this);  beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
  //初始化这个reader  initBeanDefinitionReader(beanDefinitionReader);  //将beandefinition注册到工厂中（这一步就是将bean保存到Map中）  loadBeanDefinitions(beanDefinitionReader);}

三月 22, 2018 5:09:40 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions信息: Loading XML bean definitions from class path resource [applicationContext.xml]

//设置bean类加载器//设置Spring语言表达式（SpEL）解析器//扫描ApplicationContextAware bean//注册类加载期类型切面织入（AOP）LoadTimeWeaver//为各种加载进入beanFactory的bean配置默认环境