SpringBoot @Scope与@RefreshScope注解使用详解

protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
                          @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
  //....
  // Create bean instance.
  // 单例Bean的创建
  if (mbd.isSingleton()) {
    sharedInstance = getSingleton(beanName, () -> {
      try {
        return createBean(beanName, mbd, args);
      }
      //...
    });
    bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
  }
  // 原型Bean的创建
  else if (mbd.isPrototype()) {
    // It's a prototype -> create a new instance.
    // ...
    try {
      prototypeInstance = createBean(beanName, mbd, args);
    }
    //...
    bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
  }
  else {
    // 由上面的RefreshScope注解可以知道，这里scopeName=refresh
    String scopeName = mbd.getScope();
    // 获取Refresh的Scope对象
    final Scope scope = this.scopes.get(scopeName);
    if (scope == null) {
      throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
    }
    try {
      // 让Scope对象去管理Bean
      Object scopedInstance = scope.get(beanName, () -> {
        beforePrototypeCreation(beanName);
        try {
          return createBean(beanName, mbd, args);
        }
        finally {
          afterPrototypeCreation(beanName);
        }
      });
      bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
    }
    //...
  }
}
//...
}
//...
}

public Object get(String name, ObjectFactory<?> objectFactory) {
  // 将Bean缓存下来
  BeanLifecycleWrapper value = this.cache.put(name,
                                              new BeanLifecycleWrapper(name, objectFactory));
  this.locks.putIfAbsent(name, new ReentrantReadWriteLock());
  try {
    // 创建Bean，只会创建一次，后面直接返回创建好的Bean
    return value.getBean();
  }
  catch (RuntimeException e) {
    this.errors.put(name, e);
    throw e;
  }
}

public Object get(String name, ObjectFactory<?> objectFactory) {
  // 将Bean缓存下来
  BeanLifecycleWrapper value = this.cache.put(name,
                                              new BeanLifecycleWrapper(name, objectFactory));
  this.locks.putIfAbsent(name, new ReentrantReadWriteLock());
  try {
    // 创建Bean，只会创建一次，后面直接返回创建好的Bean
    return value.getBean();
  }
  catch (RuntimeException e) {
    this.errors.put(name, e);
    throw e;
  }
}

private final ScopeCache cache;
// 这里进入上面的 BeanLifecycleWrapper value = this.cache.put(name, new BeanLifecycleWrapper(name, objectFactory));
public BeanLifecycleWrapper put(String name, BeanLifecycleWrapper value) {
  return (BeanLifecycleWrapper) this.cache.put(name, value);
}

public class StandardScopeCache implements ScopeCache {
  private final ConcurrentMap<String, Object> cache = new ConcurrentHashMap<String, Object>();
  //...
  public Object get(String name) {
    return this.cache.get(name);
  }
  // 如果不存在，才会put进去
  public Object put(String name, Object value) {
    // result若不等于null，表示缓存存在了，不会进行put操作
    Object result = this.cache.putIfAbsent(name, value);
    if (result != null) {
      // 直接返回旧对象
      return result;
    }
    // put成功，返回新对象
    return value;
  }
}

private Object bean;
public Object getBean() {
  if (this.bean == null) {
    synchronized (this.name) {
      if (this.bean == null) {
        this.bean = this.objectFactory.getObject();
      }
    }
  }
  return this.bean;
}

// 这就是我们上面一直分析的Scope对象（实际上可以看作一个保存refreshBean的Map）
private RefreshScope scope;
public synchronized Set<String> refresh() {
  // 更新上下文中Environment外部化配置值
  Set<String> keys = refreshEnvironment();
  // 调用scope对象的refreshAll方法
  this.scope.refreshAll();
  return keys;
}

ConfigurableApplicationContext addConfigFilesToEnvironment() {
	StandardEnvironment environment = copyEnvironment(
					this.context.getEnvironment());
			SpringApplicationBuilder builder = new SpringApplicationBuilder(Empty.class)
					.bannerMode(Mode.OFF).web(WebApplicationType.NONE)
					.environment(environment);
			// Just the listeners that affect the environment (e.g. excluding logging
			// listener because it has side effects)
			builder.application()
					.setListeners(Arrays.asList(new BootstrapApplicationListener(),
							new ConfigFileApplicationListener()));
			capture = builder.run();
 }

public void refreshAll() {
  // 销毁Bean
  super.destroy();
  this.context.publishEvent(new RefreshScopeRefreshedEvent());
}
public void destroy() {
  List<Throwable> errors = new ArrayList<Throwable>();
  // 缓存清空
  Collection<BeanLifecycleWrapper> wrappers = this.cache.clear();
  // ...
}

public Object get(String name, ObjectFactory<?> objectFactory) {
  // 由于刚刚清空了缓存Map，这里就会put一个新的BeanLifecycleWrapper实例
  BeanLifecycleWrapper value = this.cache.put(name,
                                              new BeanLifecycleWrapper(name, objectFactory));
  this.locks.putIfAbsent(name, new ReentrantReadWriteLock());
  try {
    // 在这里是新的BeanLifecycleWrapper实例调用getBean方法
    return value.getBean();
  }
  catch (RuntimeException e) {
    this.errors.put(name, e);
    throw e;
  }
}

public Object getBean() {
  // 由于是新的BeanLifecycleWrapper实例，这里一定为null
  if (this.bean == null) {
    synchronized (this.name) {
      if (this.bean == null) {
        // 调用IOC容器的createBean，再创建一个Bean出来
        this.bean = this.objectFactory.getObject();
      }
    }
  }
  return this.bean;
}

  public void registerBean(...){
    ...
    ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
      abd.setScope(scopeMetadata.getScopeName());
    ...
      definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
  }

public ScopeMetadata resolveScopeMetadata(BeanDefinition definition) {
          AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(
                  annDef.getMetadata(), Scope.class);
          if (attributes != null) {
              metadata.setScopeName(attributes.getString("value"));
              ScopedProxyMode proxyMode = attributes.getEnum("proxyMode");
              if (proxyMode == null || proxyMode == ScopedProxyMode.DEFAULT) {
                  proxyMode = this.defaultProxyMode;
              }
              metadata.setScopedProxyMode(proxyMode);
          }
}