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Spring源码系列-第1章-Spring源码纵览

必读

  1. 源码是循循渐进的，前面我会省略中间很多目前不需要深入的代码，所以会看起来代码比较少。省略的地方我会打上这样的标识
// ...      
或者
// ...
  1. 如果没打也不代表我没省略，可能是忘记了，不要看懵了。

第1章-Spring源码纵览

概述

Spring源码纵览这一节，主要是先了解下Spring的一些核心东西，所以前后可能关联不是特别深，跳跃性比较大，往后看就行。

简单的继承关系图

在这里插入图片描述

  • 蓝色实线箭头是指继承关系

  • 绿色虚线箭头是指接口实现关系

  • 绿色实线箭头是指接口继承关系

  • 注解版使用AnnotationConfigApplicationContext

  • XML版使用ClassPathXmlApplicationContext

Spring框架整体流程

  1. 不管是用XML还是注解也好，最终形成一份组件或者功能的配置清单。
  2. Spring用Resource来表示所有的资源
  3. 这些资源被ResourceLoader加载然后交给BeanDefinitionReader解析成BeanDefinition（Bean的定义信息：例如类名，构造方法，声明的属性等等这些信息）。BeanDefinition就是一个对象的图纸，模板。
  4. 然后将这些BeanDefinition放入到BeanDefinitionRegistry（其实就是一个Map）里，等待以后使用。
  5. 最后经过漫长的过程，根据BeanDefinition创建一个个的对象。
    （重要的一个知识点：spring是通过BeanDefinition来创建对象的，就是使用对象的图纸来创建对象，建议牢记）

核心组件接口分析

基础接口

Resource+ResourceLoader 
BeanFactory  （重要）
BeanDefinition （重要）
BeanDefinitionReader
BeanDefinitionRegistry （重要）
ApplicationContext （重要）
Aware （重要）

生命周期-后置处理器
后置处理器：看名字很难理解，这个后置是什么意思？是在什么后面执行？
我个人理解：就是在Bean实例化之后执行的一些逻辑处理器，就叫后置处理器（这里要分清一个概念：实例化和初始化：实例化就是new 出来一个对象，初始化就是给这个对象的属性等赋值）

BeanFactoryPostProcessor
InitializingBean
BeanPostProcessor

说实话，上面总结的非常不错，值得点赞

Resource资源 (个人感觉了解即可)

方法

快捷键：ctrl+F12 看类的方法

实现类

Resource实现类简单了解一下，个人感觉不做重点
快捷键：ctrl+h 查看接口实现类（这个快捷键最经常使用）

  1. ContextResource：表示可以拿Web环境的资源
  2. HttpResource：可以从网络中拿到资源
  3. WritableResource：
    1. FileSystemResource：可以从文件系统拿到资源
    2. FileUrlResource：URL就是统一资源定位符的意思；URL可以定位到网络，磁盘，等任何你想定位到的位置；表示Spring几乎可以从任何地方拿到资源。
  4. AbstractResource
    1. ByteArrayResource：从byte数组拿到资源
    2. InputStreamResource：从Input流中拿到资源
  5. 综合来说Spring几乎可以从任何地方拿到资源。

ResourceLoader资源加载器

此类的源码开头有这样一句话，Strategy interface（策略接口），显然用到了策略模式。策略体现在哪个地方，我们下面再说。

Strategy interface for loading resources (e.g., class path or file systemresources)

方法
/**
 * Strategy interface（策略接口） for loading resources (e.g., class path or file system
 * resources). An {@link org.springframework.context.ApplicationContext}
 * is required to provide this functionality plus extended
 * {@link org.springframework.core.io.support.ResourcePatternResolver} support.
 *
 * <p>{@link DefaultResourceLoader} is a standalone implementation that is
 * usable outside an ApplicationContext and is also used by {@link ResourceEditor}.
 *
 * <p>Bean properties of type {@code Resource} and {@code Resource[]} can be populated
 * from Strings when running in an ApplicationContext, using the particular
 * context's resource loading strategy.
 *
 * @author Juergen Hoeller
 * @since 10.03.2004
 * @see Resource
 * @see org.springframework.core.io.support.ResourcePatternResolver
 * @see org.springframework.context.ApplicationContext
 * @see org.springframework.context.ResourceLoaderAware
 */
public interface ResourceLoader {

   /** Pseudo URL prefix for loading from the class path: "classpath:". */
   String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;
   /**
    * Return a {@code Resource} handle for the specified resource location.
    * <p>The handle should always be a reusable resource descriptor,
    * allowing for multiple {@link Resource#getInputStream()} calls.
    * <p><ul>
    * <li>Must support fully qualified URLs, e.g. "file:C:/test.dat".
    * <li>Must support classpath pseudo-URLs, e.g. "classpath:test.dat".
    * <li>Should support relative file paths, e.g. "WEB-INF/test.dat".
    * (This will be implementation-specific, typically provided by an
    * ApplicationContext implementation.)
    * </ul>
    * <p>Note that a {@code Resource} handle does not imply an existing resource;
    * you need to invoke {@link Resource#exists} to check for existence.
    * @param location the resource location
    * @return a corresponding {@code Resource} handle (never {@code null})
    * @see #CLASSPATH_URL_PREFIX
    * @see Resource#exists()
    * @see Resource#getInputStream()
    */
   Resource getResource(String location); //这个是最关键的
   /**
    * Expose the {@link ClassLoader} used by this {@code ResourceLoader}.
    * <p>Clients which need to access the {@code ClassLoader} directly can do so
    * in a uniform manner with the {@code ResourceLoader}, rather than relying
    * on the thread context {@code ClassLoader}.
    * @return the {@code ClassLoader}
    * (only {@code null} if even the system {@code ClassLoader} isn't accessible)
    * @see org.springframework.util.ClassUtils#getDefaultClassLoader()
    * @see org.springframework.util.ClassUtils#forName(String, ClassLoader)
    */
   @Nullable
   ClassLoader getClassLoader();

}
实现类

  1. DefaultResourceLoader：默认资源加载器
    1. ClassRelativeResourceLoader：能读取类路径相对路径
    2. FileSystemResourceLoader：能读取文件系统的
    3. ServletContextResourceLoader：能读取web环境的

BeanFactory-Bean工厂

保存很多的BeanDefinition信息,都有一个唯一的名字，提供getBean()方法

/**
 * The root interface for accessing a Spring bean container.
 * 根接口，整个访问容器的入口
 * <p>This is the basic client view of a bean container;
 * further interfaces such as {@link ListableBeanFactory} and
 * {@link org.springframework.beans.factory.config.ConfigurableBeanFactory}
 * are available for specific purposes.
 *
 * <p>This interface is implemented by objects that hold a number of bean definitions,
 * 保存很多的BeanDefinition信息,都有一个唯一的名字
 * each uniquely identified by a String name. Depending on the bean definition,
 * the factory will return either an independent instance of a contained object
 * (the Prototype design pattern【原型模式】), or a single shared instance (a superior
 * alternative to the Singleton design pattern【单例设计模式】, in which the instance is a
 * singleton in the scope of the factory). Which type of instance will be returned
 * depends on the bean factory configuration: the API is the same. Since Spring
 * 2.0, further scopes are available depending on the concrete application
 * context (e.g. "request" and "session" scopes in a web environment).
 *
 */
public interface BeanFactory {
    //省略...
}

源码分析小技巧：看源码时，我们可以先看一个类的接口继承关系，因为接口就是规范，大部分开源框架源码都是遵守这一规范的。
在这里插入图片描述

  1. BeanFactory
    1. HierarchicalBeanFactory：定义父子工厂（父子容器）
    2. ListableBeanFacotory：实现是DefaultListableBeanFactory，保存了ioc容器中的核心信息。（Listable是可列举的，可管理的。保存的核心信息是什么？当然要有bean了）
    3. AutowireCapableBeanFactory：提供自动装配能力
      4. AnnotationApplicationContext：组合了一个总的注册中心（DefaultListableBeanFactory），它有自动装配能力。
AbstractApplicationContext

在这里插入图片描述
环境类的意思就是谁持有这个策略；这里就解释了上文说ResourceLoader是环境类接口（怎么会冒出来一句这样的话？为了解释环境类是什么？）

	// 策略模式的环境类
	private ResourcePatternResolver resourcePatternResolver;

	public AbstractApplicationContext() {
		this.resourcePatternResolver = getResourcePatternResolver();
	}
GenericApplicationContext

在这里插入图片描述

这里组合了DefaultListableBeanFactory，这是一个非常重要的类，保存了beanDefinition

public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry {

   private final DefaultListableBeanFactory beanFactory;
   
}
DefaultListableBeanFactory
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
      implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {

   /** Map from serialized id to factory instance. */

   //组合模式,Spring里面可以有很多工厂，每一个工厂有自己的ID，好处就是工厂之间的bean可以隔离起来，但是用的很少
   private static final Map<String, Reference<DefaultListableBeanFactory>> serializableFactories =
         new ConcurrentHashMap<>(8);


   /**如果容器中有Map<Class, Object[]/String[] ></> Map of bean definition objects, keyed by bean name. */
   //所有BeanDefinition信息按照名字对应BeanDefinition关系都保存好了。这个名称默认应该就是类名首字母小写，单独指定名称的除外
   private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);


   /** Map of singleton-only bean names, keyed by dependency type. */
   //Spring中按照类型得到组件名称的一个底层池
    //车的图纸和车的关系。这里只保存图纸(也就是类信息)，对象存哪里呢？往后看
   private final Map<Class<?>, String[]> singletonBeanNamesByType = new ConcurrentHashMap<>(64);

   /** List of bean definition names, in registration order. */
   //保存所有BeanDefinition的名字。
   private volatile List<String> beanDefinitionNames = new ArrayList<>(256);

在这里插入图片描述

  1. BeanDefinitionRegistry：Bean定义信息注册中心（map,key默认是类名首字母小写，比如ApplicationRunnerImpl类注册的key为applicationRunnerImpl,也可指定名称）
  2. SimpleAliasRegistry：别名注册中心
  3. SingletonBeanRegistry：单实例注册中心
  4. BeanFactory：Bean工厂
  5. AutowireCapableBeanFactory：有自动装配能力的Bean工厂
  6. DefaultListableBeanFactory：可以理解为拥有上面所有注册中心功能的一个总的注册中心
  7. GenericApplicationContext有一个我们常用的实现类AnnotationConfigApplicationContext，就是注解版的IOC容器（Generic：通用的）
  8. 虽然我们的IOC容器和DefaultListableBeanFactory没有继承的父子关系，但是却组合了DefaultListableBeanFactory，拥有了它的全部功能。
  9. DefaultListableBeanFactory在Spring中扮演着至关重要的角色（保存了所有对象（bean）的图纸（也就是类模板），并没有真正存对象）。
  1. DefaultListableBeanFactory保存了所有对象（bean）的图纸（也就是类模板），并没有真正存对象。
  2. 我们这里猜想一下，Spring底层真正存Bean的地方用的是哪个数据结构呢？是List，还是Set，还是Map。咱们稍微想一下就知道肯定是Map，并且Key是beanName，value是真正的Bean。如果不是Map的话，如何通过BeanName拿到对应的Bean呢？
  3. 其实就是上面的那个beanDefinitionMap

注册BeanDefinition-1

流程图-BeanDefinition注册流程

这个注册流程，也可以理解为如何在方法间调用，然后一步步完成类的BeanDefinition的创建和保存,obtainFreshBeanFactory()方法，获取beanFactory,意思就是构建好所有类的模板图纸，这样就算准备好了这个bean工厂了
在这里插入图片描述
在这里插入图片描述

  • 我们要看BeanDefinition是何时被放入到beanDefinitionMap，只需要在DefaultListableBeanFactory用到beanDefinitionMap.put()的地方打个断点。
  • 我们在DefaultListableBeanFactory里搜索，发现了registerBeanDefinition（注册Bean定义信息）这个方法名很像我们要找的东西，再看里面的代码，果然有beanDefinitionMap.put()这串代码，我们试着在这里打个断点
  • 然后启动下面的测试类
  • 上面就是我们看一个框架源码，可以往哪些方向去猜测。
MainTest测试类

有时间的话可以按照下面的操作一步一步看一下源码，这里只要记住 AbstractApplicationContext#obtainFreshBeanFactory()就是把所有需要注册的类的模板信息beanDefinition放到map中，以便下一步创建bean时使用

public class MainTest {

   public static void main(String[] args) throws IOException {
      ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
      Person bean = context.getBean(Person.class);
      System.out.println(bean);

   }
}
Debug调用栈

调用栈的调用顺序已经非常清楚了，可以把图放大一点看，下面只说一些必要的信息。

  1. new ClassPathXmlApplicationContext("beans.xml")这一步开始就要刷新容器了

  2. 调用AbstractApplicationContext#refresh()这个方法，refresh()方法是容器刷新的几大步所在地

AbstractApplicationContext#refresh()容器刷新
    @Override
    public void refresh() throws BeansException, IllegalStateException {
       synchronized (this.startupShutdownMonitor) {
          StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

          // Prepare this context for refreshing.
          prepareRefresh();

          // Tell the subclass to refresh the internal bean factory.
          // BeanFactory第一次开始创建的时候,有xml解析逻辑。
          ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

          // Prepare the bean factory for use in this context.
          prepareBeanFactory(beanFactory);

          try {
            // ......
             // Instantiate all remaining (non-lazy-init) singletons.
             //完成 BeanFactory 初始化
             finishBeanFactoryInitialization(beanFactory);

             // Last step: publish corresponding event.
             finishRefresh();
          }
          // ......
       }
    }
AbstractApplicationContext#obtainFreshBeanFactory()第一次开始创建BeanFactory
    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
       refreshBeanFactory(); //刷新整个BeanFactory
       return getBeanFactory();
    }
AbstractRefreshableApplicationContext#refreshBeanFactory()刷新整个BeanFactory
    protected final void refreshBeanFactory() throws BeansException {
       if (hasBeanFactory()) {
          destroyBeans();
          closeBeanFactory();
       }
       try {
          DefaultListableBeanFactory beanFactory = createBeanFactory(); //创建保存所有Bean定义信息的档案馆
          beanFactory.setSerializationId(getId());
          customizeBeanFactory(beanFactory);
          loadBeanDefinitions(beanFactory); //开始加载Bean定义信息
          this.beanFactory = beanFactory;
       }
       catch (IOException ex) {
          throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
       }
    }
AbstractXmlApplicationContext#loadBeanDefinitions()加载Bean定义信息

通过这个方法的名称就可以看出来这是给容器中加载类的BeanDefinition

下面就是一堆的loadBeanDefinitions调用，调用顺序就是我下面写的代码顺序。

    
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
       // Create a new XmlBeanDefinitionReader for the given BeanFactory. 准备读取xml内容的读取器
       XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

       // Configure the bean definition reader with this context's
       // resource loading environment.
       beanDefinitionReader.setEnvironment(this.getEnvironment());
       beanDefinitionReader.setResourceLoader(this); //持有ioc容器的环境类
       beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

       // Allow a subclass to provide custom initialization of the reader,
       // then proceed with actually loading the bean definitions.
       initBeanDefinitionReader(beanDefinitionReader);
       loadBeanDefinitions(beanDefinitionReader);
    }

	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations(); //可以一次传入很多配置文件
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations); //读取文件
		}
	}
AbstractBeanDefinitionReader#loadBeanDefinitions()

下面也是一堆的loadBeanDefinitions调用，调用顺序就是我下面写的代码顺序。

    @Override
    public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
        Assert.notNull(locations, "Location array must not be null");
        int count = 0;
        for (String location : locations) { //加载每一个配置文件里面的内容
            count += loadBeanDefinitions(location);
        }
        return count;
    }

    @Override  //加载指定配置文件的所有内容
    public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
        return loadBeanDefinitions(location, null);
    }

	public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
		ResourceLoader resourceLoader = getResourceLoader();
		if (resourceLoader == null) {
			throw new BeanDefinitionStoreException(
					"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
		}

		if (resourceLoader instanceof ResourcePatternResolver) {
			// Resource pattern matching available.
			try {
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location); //得到实体文件对应的资源
				int count = loadBeanDefinitions(resources);
				if (actualResources != null) {
					Collections.addAll(actualResources, resources);
				}
				if (logger.isTraceEnabled()) {
					logger.trace("Loaded " + count + " bean definitions from location pattern [" + location + "]");
				}
				return count;
			}
			catch (IOException ex) {
				throw new BeanDefinitionStoreException(
						"Could not resolve bean definition resource pattern [" + location + "]", ex);
			}
		}
		else {
			// Can only load single resources by absolute URL. 这里开始转换成我们前面说的Resource资源
			Resource resource = resourceLoader.getResource(location);
			int count = loadBeanDefinitions(resource);
			if (actualResources != null) {
				actualResources.add(resource);
			}
			if (logger.isTraceEnabled()) {
				logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
			}
			return count;
		}
	}

	public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
		Assert.notNull(resources, "Resource array must not be null");
		int count = 0;
		for (Resource resource : resources) {
			count += loadBeanDefinitions(resource);
		}
		return count;
	}
XmlBeanDefinitionReader#loadBeanDefinitions()

又是一堆loadBeanDefinitions调用

    @Override
    public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
       // 这里是个适配器模式 对接 InputStreamSource 和 Resource 或者说是个装饰器模式也可以
       return loadBeanDefinitions(new EncodedResource(resource));
    }


	public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
		Assert.notNull(encodedResource, "EncodedResource must not be null");
		if (logger.isTraceEnabled()) {
			logger.trace("Loading XML bean definitions from " + encodedResource);
		}

		Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();

		if (!currentResources.add(encodedResource)) {
			throw new BeanDefinitionStoreException(
					"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
		}

		try (InputStream inputStream = encodedResource.getResource().getInputStream()) {
			InputSource inputSource = new InputSource(inputStream);
			if (encodedResource.getEncoding() != null) {
				inputSource.setEncoding(encodedResource.getEncoding());
			}
			return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"IOException parsing XML document from " + encodedResource.getResource(), ex);
		}
		finally {
			currentResources.remove(encodedResource);
			if (currentResources.isEmpty()) {
				this.resourcesCurrentlyBeingLoaded.remove();
			}
		}
	}


	protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {

		try {
			Document doc = doLoadDocument(inputSource, resource); //利用dom解析工具把xml变成Document
			int count = registerBeanDefinitions(doc, resource); //开始注册了
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + count + " bean definitions from " + resource);
			}
			return count;
		}
		catch (BeanDefinitionStoreException ex) {
			throw ex;
		}
		catch (SAXParseException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
		}
		catch (SAXException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"XML document from " + resource + " is invalid", ex);
		}
		catch (ParserConfigurationException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Parser configuration exception parsing XML from " + resource, ex);
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"IOException parsing XML document from " + resource, ex);
		}
		catch (Throwable ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Unexpected exception parsing XML document from " + resource, ex);
		}
	}


	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getRegistry().getBeanDefinitionCount();
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}
DefaultBeanDefinitionDocumentReader#registerBeanDefinitions()注册Bean定义信息
    @Override
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
       this.readerContext = readerContext;
       doRegisterBeanDefinitions(doc.getDocumentElement());
    }

	protected void doRegisterBeanDefinitions(Element root) {
		// this behavior emulates a stack of delegates without actually necessitating one.
		BeanDefinitionParserDelegate parent = this.delegate; //由这个类进行最终解析
		this.delegate = createDelegate(getReaderContext(), root, parent);
		
        //省略不重要的代码......
		preProcessXml(root);
		parseBeanDefinitions(root, this.delegate);
		postProcessXml(root);

		this.delegate = parent;
	}

	//省略不重要的代码......

	//最后经过一些列的document文档遍历解析，走到了下面这个方法
	protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); //把当前标签解析完了，BeanDefinition和beanName都封装在了Holder中
		if (bdHolder != null) {
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error("Failed to register bean definition with name '" +
						bdHolder.getBeanName() + "'", ele, ex);
			}
			// Send registration event.  //发送一个通知事件
			getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
		}
	}
BeanDefinitionReaderUtils#registerBeanDefinition()
    public static void registerBeanDefinition(
          BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
          throws BeanDefinitionStoreException {

       // Register bean definition under primary name.
       String beanName = definitionHolder.getBeanName();
       registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

       // Register aliases for bean name, if any. 别名
       String[] aliases = definitionHolder.getAliases();
       if (aliases != null) {
          for (String alias : aliases) {
             registry.registerAlias(beanName, alias);
          }
       }
    }
DefaultListableBeanFactory#registerBeanDefinition()
    //终于走到了这最后一步
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
        //先看beanDefinitionMap有没有，没有我才注册
        if (existingDefinition != null) {

            //省略一系列目前来说不重要的判断......

            this.beanDefinitionMap.put(beanName, beanDefinition);
        }
        else {
            if (hasBeanCreationStarted()) {
                // Cannot modify startup-time collection elements anymore (for stable iteration)
                synchronized (this.beanDefinitionMap) {
                    this.beanDefinitionMap.put(beanName, beanDefinition); //注册进去了
                    List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    removeManualSingletonName(beanName);
                }
            }
            else {
                // Still in startup registration phase
                this.beanDefinitionMap.put(beanName, beanDefinition);
                this.beanDefinitionNames.add(beanName);
                removeManualSingletonName(beanName);
            }
            this.frozenBeanDefinitionNames = null;
        }

        if (existingDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
        else if (isConfigurationFrozen()) {
            clearByTypeCache();
        }
    }

注册BeanDefinition-2

Debug调用栈
  • 还有一个debug的猜测方向，想要注册BeanDefinition肯定要new，我们可以直接在AbstractBeanDefinition这个抽象父类的构造函数打断点，我们不知道会走哪个构造函数，所以给三个构造函数都打断点。
  • 下面就是打完断点之后，运行MainTest测试类后的调用栈

前面的调用栈都是一样的，从下面开始不一样

DefaultBeanDefinitionDocumentReader#processBeanDefinition()
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
       BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); //把当前标签解析完了，BeanDefinition和beanName都封装在了Holder中
       if (bdHolder != null) {
          bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
          try {
             // Register the final decorated instance.
             BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
          }
          catch (BeanDefinitionStoreException ex) {
             getReaderContext().error("Failed to register bean definition with name '" +
                   bdHolder.getBeanName() + "'", ele, ex);
          }
          // Send registration event.  //发送一个通知事件
          getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
       }
    }
BeanDefinitionParserDelegate#parseBeanDefinitionElement()
    public static final String ID_ATTRIBUTE = "id";

    public static final String NAME_ATTRIBUTE = "name";


    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
       String id = ele.getAttribute(ID_ATTRIBUTE);
       String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

       List<String> aliases = new ArrayList<>();
       if (StringUtils.hasLength(nameAttr)) {
          String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
          aliases.addAll(Arrays.asList(nameArr));
       }

       String beanName = id; //为什么说id就是BeanName，Spring源码这里自己写的
       if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
          beanName = aliases.remove(0);
          if (logger.isTraceEnabled()) {
             logger.trace("No XML 'id' specified - using '" + beanName +
                   "' as bean name and " + aliases + " as aliases");
          }
       }

       if (containingBean == null) {
          checkNameUniqueness(beanName, aliases, ele);
       }

       AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
		 //  省略部分代码......
          String[] aliasesArray = StringUtils.toStringArray(aliases);
          return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
       }

       return null;
    }


	public AbstractBeanDefinition parseBeanDefinitionElement(
			Element ele, String beanName, @Nullable BeanDefinition containingBean) {

		this.parseState.push(new BeanEntry(beanName));

		String className = null;
		if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
			className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
		}
		String parent = null;
		if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
			parent = ele.getAttribute(PARENT_ATTRIBUTE);
		}

		try {
			AbstractBeanDefinition bd = createBeanDefinition(className, parent);

			parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
			bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
			//以下是解析Bean标签里面的元数据填充完 BeanDefinition
			parseMetaElements(ele, bd);
			parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
			parseReplacedMethodSubElements(ele, bd.getMethodOverrides());

			parseConstructorArgElements(ele, bd);
			parsePropertyElements(ele, bd);
			parseQualifierElements(ele, bd);

			bd.setResource(this.readerContext.getResource());
			bd.setSource(extractSource(ele));

			return bd;
		}
		catch (ClassNotFoundException ex) {
			error("Bean class [" + className + "] not found", ele, ex); //这个就是我们常见的错误
		}
		catch (NoClassDefFoundError err) {
			error("Class that bean class [" + className + "] depends on not found", ele, err);
		}
		catch (Throwable ex) {
			error("Unexpected failure during bean definition parsing", ele, ex);
		}
		finally {
			this.parseState.pop();
		}

		return null;
	}


	protected AbstractBeanDefinition createBeanDefinition(@Nullable String className, @Nullable String parentName)
			throws ClassNotFoundException {

		return BeanDefinitionReaderUtils.createBeanDefinition(
				parentName, className, this.readerContext.getBeanClassLoader());
	}
BeanDefinitionReaderUtils#createBeanDefinition()
    public static AbstractBeanDefinition createBeanDefinition(
          @Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException {

       GenericBeanDefinition bd = new GenericBeanDefinition(); //创建了一个BeanDefintion准备封装标签的内容
       bd.setParentName(parentName);
       if (className != null) {
          if (classLoader != null) {
             bd.setBeanClass(ClassUtils.forName(className, classLoader));
          }
          else {
             bd.setBeanClassName(className);
          }
       }
       return bd;
    }

至此结束，上面的都不是很难，顺着调用栈就能看懂。

ApplicationContext接口功能

  1. ioc事件派发器
  2. 国际化解析
  3. bean工厂功能—自动装配被组合进来的
  4. 资源解析功能
  5. 等等

这个就是我们常说的IOC容器

Aware接口功能分析

  1. aware中文翻译是意识到的，察觉到的，发现这么个意思。从翻译来看，aware做的事情应该是发现某一个东西。
/**
 * Marker superinterface indicating that a bean is eligible to be
 * notified by the Spring container of a particular framework object
 * through a callback-style method. Actual method signature is
 * determined by individual subinterfaces, but should typically
 * consist of just one void-returning method that accepts a single
 * argument.
 */
public interface Aware {

}
  1. 注释的大致意思是：Aware是一个标记性的超接口（顶级接口），指示了一个Bean有资格通过回调方法的形式获取Spring容器底层组件。实际回调方法被定义在每一个子接口中，而且通常一个子接口只包含一个接口一个参数并且返回值为void的方法。
  2. 说白了：只要实现了Aware子接口的Bean都能获取到一个Spring底层组件。

比如实现了ApplicationContextAware接口，实现它的方法，就能通过回调机制拿到ApplicationContext

创建Person对象
流程图-Bean对象创建流程


在这里插入图片描述

Debug调用栈

为了知道Aware的原理，我们给上面的pos_1和pos_2位置打上断点，看下是怎么进来的

Person

@Component
public class Person implements ApplicationContextAware, MessageSourceAware {

   ApplicationContext context;  //我们不用@Autowired也可以要到ioc容器
   MessageSource messageSource;
    
   	public void setName(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	} 
    
   public Person(){
	  System.out.println("person创建....");  //pos_1
   }

   @Override
   public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
      //利用回调机制，把ioc容器传入
      this.context = applicationContext;  //pos_2
   }

   @Override
   public void setMessageSource(MessageSource messageSource) {
      this.messageSource = messageSource;
   }
}

AnnotationMainTest

/**
 * 注解版Spring的用法
 */
public class AnnotationMainTest {

   public static void main(String[] args) {
      ApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfig.class);
      Person bean = applicationContext.getBean(Person.class);
      ApplicationContext context = bean.getContext();

      System.out.println(context == applicationContext);
   }

MainConfig

@ComponentScan("cn.imlql.spring")
@Configuration
public class MainConfig {
   
   public Person person(){
      Person person = new Person();
      person.setName("李四");
      return person;
   }
}

  1. 有一些一样的东西不再赘述
  2. 在AbstractApplicationContext#refresh()里会调用
AbstractApplicationContext#finishBeanFactoryInitialization()完成 BeanFactory 初始化
    @Override
    public void refresh() throws BeansException, IllegalStateException {
       synchronized (this.startupShutdownMonitor) {
          StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

          // BeanFactory第一次开始创建的时候,有xml解析逻辑,生成bean对应的definition。
          ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
		 // ...
          try {                
             // Instantiate all remaining (non-lazy-init) singletons.
             //完成 BeanFactory 初始化(生成对应的对象实例)
             finishBeanFactoryInitialization(beanFactory);
          }
       }
    }

	protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		// Instantiate all remaining (non-lazy-init) singletons.
		//初始化所有的单实例Bean
		beanFactory.preInstantiateSingletons();
	}
DefaultListableBeanFactory#preInstantiateSingletons()循环遍历beanDefinitionName
    @Override
    public void preInstantiateSingletons() throws BeansException {
       if (logger.isTraceEnabled()) {
          logger.trace("Pre-instantiating singletons in " + this);
       }

       List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

       // Trigger initialization of all non-lazy singleton beans...
       for (String beanName : beanNames) {//挨个遍历beanDefinitionName
          RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
          if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
             if (isFactoryBean(beanName)) {
                // ...
             }
             else {
                getBean(beanName);
             }
          }
       }

    }
AbstractBeanFactory#getBean()准备获取Bean
    @Override
    public Object getBean(String name) throws BeansException {
       return doGetBean(name, null, null, false);
    }

	protected <T> T doGetBean(
			String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
			throws BeansException {

		String beanName = transformedBeanName(name); //转换Bean名字
		Object beanInstance;

		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName); //检查缓存中有没有
		if (sharedInstance != null && args == null) {
			//...
		}

		else {
			//...
			try {
				String[] dependsOn = mbd.getDependsOn();
				if (dependsOn != null) {
					for (String dep : dependsOn) { //看当前Bean有没有依赖其他Bean

						try {
							getBean(dep); //依赖了其他bean，就先获取其他的哪些bean
						}
						//...
					}
				}

				// Create bean instance. 创建bean的实例，下面是一个lamda表达式
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args);  //创建bean对象的实例
						}
					});
					beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}
		}

		return adaptBeanInstance(name, beanInstance, requiredType);
	}
DefaultSingletonBeanRegistry#getSingleton()
    public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
       Assert.notNull(beanName, "Bean name must not be null");
       synchronized (this.singletonObjects) {
        	// ...
             try {
                // 通过getObject获取真正的对象，有点类似于FactoryBean（这个不懂的建议先了解下Spring基本用法），
                // ObjectFactory类注释有说明。
                singletonObject = singletonFactory.getObject();
                newSingleton = true;
                // ...
             }

          return singletonObject;
       }
    }

下面就开始分析lamda表达式里的东西

AbstractAutowireCapableBeanFactory#createBean()
    protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
          throws BeanCreationException {
	   //...
       try {
          Object beanInstance = doCreateBean(beanName, mbdToUse, args);
          if (logger.isTraceEnabled()) {
             logger.trace("Finished creating instance of bean '" + beanName + "'");
          }
          return beanInstance;
       }
    }

    protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
        throws BeanCreationException {
		//...
        if (instanceWrapper == null) {
            //创建Bean的实例,默认使用无参构造器创建的对象
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
    }

	protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
        //...
        return instantiateBean(beanName, mbd);
    }
	
	/** 指定Bean的创建策略；可以用jdk的反射，可以用cglib创建子类对象 Strategy for creating bean instances. */
	private InstantiationStrategy instantiationStrategy;
	protected BeanWrapper instantiateBean(String beanName, RootBeanDefinition mbd) {
		try {
			Object beanInstance;
			else {
				beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, this);
			}
			BeanWrapper bw = new BeanWrapperImpl(beanInstance);
			initBeanWrapper(bw);
			return bw;
		}
	}
SimpleInstantiationStrategy#instantiate()反射创建Bean
    public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
       // Don't override the class with CGLIB if no overrides.
       if (!bd.hasMethodOverrides()) {
          return BeanUtils.instantiateClass(constructorToUse);
       }
    }
Spring内部的BeanUtils反射工具

这个类是Spring内部提供的反射工具类，平时项目你也可以用上，就不用自己写反射了

  	  public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
       Assert.notNull(ctor, "Constructor must not be null");
       try {
          ReflectionUtils.makeAccessible(ctor);
          else {        
             Object[] argsWithDefaultValues = new Object[args.length];        
             return ctor.newInstance(argsWithDefaultValues);
          }
       }
    }
	// 后面就是反射创建Person
Aware回调原理
Debug调用栈

前面有很多一样的调用链，不再赘述。从doCreateBean:602调用栈开始不一样

AbstractAutowireCapableBeanFactory#doCreateBean()
    protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
          throws BeanCreationException {

       // Initialize the bean instance.
       Object exposedObject = bean;
       try {
          populateBean(beanName, mbd, instanceWrapper);
          exposedObject = initializeBean(beanName, exposedObject, mbd);
       }
    }

	
	protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
		Object wrappedBean = bean;
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}
		return wrappedBean;
	}


	public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessBeforeInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}
ApplicationContextAwareProcessor
    @Override
    @Nullable
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
       if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
             bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
             bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware ||
             bean instanceof ApplicationStartupAware)) {
          return bean;
       }
       //...
       else {
          invokeAwareInterfaces(bean); //执行aware接口规定的方法
       }

       return bean;
    }

	//就是在这里执行Aware回调
	private void invokeAwareInterfaces(Object bean) {
		if (bean instanceof EnvironmentAware) {
			((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
		}
		if (bean instanceof EmbeddedValueResolverAware) {
			((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
		}
		if (bean instanceof ResourceLoaderAware) {
			((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
		}
		if (bean instanceof ApplicationEventPublisherAware) {
			((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
		}
		if (bean instanceof MessageSourceAware) {
			((MessageSourceAware) bean).setMessageSource(this.applicationContext);
		}
		if (bean instanceof ApplicationStartupAware) {
			((ApplicationStartupAware) bean).setApplicationStartup(this.applicationContext.getApplicationStartup());
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}

属性赋值的时机（XML版）

Debug调用栈

Person

public class Person implements ApplicationContextAware, MessageSourceAware {

   ApplicationContext context;  //我们不用@Autowired也可以要到ioc容器
   MessageSource messageSource;
    
   	public void setName(String name) {
		this.name = name;  // pos_2
	}

	public String getName() {
		return name;
	} 
    
   public Person(){
	  System.out.println("person创建....");  //pos_1
   }

   @Override
   public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
      //利用回调机制，把ioc容器传入
      this.context = applicationContext;  
   }

   @Override
   public void setMessageSource(MessageSource messageSource) {
      this.messageSource = messageSource;
   }
}

MainTest

public class MainTest {

	public static void main(String[] args) {
		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
		Person bean = context.getBean(Person.class);
		System.out.println(bean);
	}

}

beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

	<bean class="cn.imlql.spring.bean.Person" id="person">
		<property name="name" value="张三"/>
 	</bean>

</beans>

为了知道属性赋值的时机，这里要给setXXX方法打断点，也就是上面的pos_1和pos_2位置打断点。

还是老规矩，一样的就不说了，从调用栈不一样的地方开始说起。多看几遍，看到后面就会发现思路越来越清晰了。

AbstractAutowireCapableBeanFactory#doCreateBean()

	protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
			throws BeanCreationException {

		// Instantiate the bean.  这里面封装好了真正的Person对象
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			//创建Bean的实例,默认使用无参构造器创建的对象
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
        
		//......

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper); //给创建好的对象每个属性进行赋值
			exposedObject = initializeBean(beanName, exposedObject, mbd);//初始化bean
		}
		return exposedObject;
	}

我们看到此时，Person的name属性还是null

AbstractAutowireCapableBeanFactory#populateBean()属性赋值

    protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
        // 这一步就是拿到属性值
        PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
        
        // ......      

        if (pvs != null) {
            applyPropertyValues(beanName, mbd, bw, pvs); //xml版的所有配置会来到这里给属性赋值
        }
    }

这里拿到属性值

    protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
        // ......

        // Set our (possibly massaged) deep copy.
        try { //深拷贝所有PropertyValue应该对应的属性
            bw.setPropertyValues(new MutablePropertyValues(deepCopy));
        }
    }


bw就是上面说的 => 里面封装好了真正的Person对象

这里就是一层一层调，不重要跳过。

AbstractNestablePropertyAccessor#processLocalProperty

private void processLocalProperty(PropertyTokenHolder tokens, PropertyValue pv) {
		// ...
		try {
			Object originalValue = pv.getValue();
			Object valueToApply = originalValue;
			ph.setValue(valueToApply);
		}
		//...
	}

BeanWrapperImpl内部类BeanPropertyHandler#setValue()

private class BeanPropertyHandler extends PropertyHandler { 
	@Override
    public void setValue(@Nullable Object value) throws Exception {
       Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
             ((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
             this.pd.getWriteMethod());
       if (System.getSecurityManager() != null) {
          AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
             ReflectionUtils.makeAccessible(writeMethod);
             return null;
          });
          try {
             AccessController.doPrivileged((PrivilegedExceptionAction<Object>)
                   () -> writeMethod.invoke(getWrappedInstance(), value), acc);
          }
          catch (PrivilegedActionException ex) {
             throw ex.getException();
          }
       }
       else {
          ReflectionUtils.makeAccessible(writeMethod);
           // 这里的意思就是找到这个属性的写方法，所谓写方法就是setxxx方法
          writeMethod.invoke(getWrappedInstance(), value);
       }
    }
}


最后就是反射走到了我们的Person#setName(String name)

再来看看messageSource何时赋值


剩下的在上面的Aware回调原理讲过

属性赋值的时机（注解版）

Debug调用栈

AnnotationMainTest

public class AnnotationMainTest {
   public static void main(String[] args) {

      ApplicationContext applicationContext =
            new AnnotationConfigApplicationContext(MainConfig.class);

      Person bean = applicationContext.getBean(Person.class);
      ApplicationContext context = bean.getContext();
      System.out.println(context == applicationContext);
   }
}

Cat

@Component
public class Cat {

   public Cat(){
      System.out.println("cat被创建了...");
   }

   private String name;


   @Value("${JAVA_HOME}") //自动赋值功能
   public void setName(String name) {
      System.out.println("cat....setName正在赋值调用....");
      this.name = name;
   }

   public String getName() {
      return name;
   }
}

MainConfig

@ComponentScan("cn.imlql.spring")
@Configuration
public class MainConfig {

   public MainConfig(){
      System.out.println("MainConfig...创建了....");
   }

   public Person person(){
      Person person = new Person();
      person.setName("李四");
      return person;
   }
}

Person

@Component
public class Person implements ApplicationContextAware, MessageSourceAware {

   ApplicationContext context;  //可以要到ioc容器  
   
   MessageSource messageSource;
   
   private String name;
   
   private Cat cat;


   public Person(){
      System.out.println("person创建....");
   }


   public void setName(String name) {
      this.name = name;
   }

   public String getName() {
      return name;
   }



   @Autowired  //去发现一下.....
   public void setCat(Cat cat) {
      this.cat = cat;
   }

   public Cat getCat() {
      return cat;
   }

   @Override
   public String toString() {
      return "Person{" +
            "name='" + name + '\'' +
            '}';
   }


   public ApplicationContext getContext() {
      return context;
   }

   @Override
   public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
      //利用回调机制，把ioc容器传入
      this.context = applicationContext;
   }

   @Override
   public void setMessageSource(MessageSource messageSource) {
      this.messageSource = messageSource;
   }
}

老样子，只看不一样的调用栈

AbstractAutowireCapableBeanFactory#populateBean()

    protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {

       // ......
       PropertyDescriptor[] filteredPds = null;
       if (hasInstAwareBpps) {
          if (pvs == null) {
             pvs = mbd.getPropertyValues();
          }
          for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
             // 注解版的属性赋值会走这里
             PropertyValues pvsToUse = bp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
             if (pvsToUse == null) {
                if (filteredPds == null) {
                   filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
                }
                pvsToUse = bp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                if (pvsToUse == null) {
                   return;
                }
             }
             pvs = pvsToUse;
          }
       }
       if (needsDepCheck) {
          if (filteredPds == null) {
             filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
          }
          checkDependencies(beanName, mbd, filteredPds, pvs);
       }

       if (pvs != null) {
          applyPropertyValues(beanName, mbd, bw, pvs); //xml版的所有配置会来到这里给属性赋值
       }
    }

这里有一个非常著名的后置处理器，AutowiredAnnotationBeanPostProcessor自动装配注解后置处理器，顾名思义就是用来处理@Autowired注解自动装配的。

AutowiredAnnotationBeanPostProcessor#postProcessProperties()

    public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {
       InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);//找到自动装配的元信息
       try {
          metadata.inject(bean, beanName, pvs);
       }
       catch (BeanCreationException ex) {
          throw ex;
       }
       catch (Throwable ex) {
          throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
       }
       return pvs;
    }

下面的代码不在debug调用栈里，但是也比较重要

    private InjectionMetadata findAutowiringMetadata(String beanName, Class<?> clazz, @Nullable PropertyValues pvs) {
       // Fall back to class name as cache key, for backwards compatibility with custom callers.
       String cacheKey = (StringUtils.hasLength(beanName) ? beanName : clazz.getName());
       // Quick check on the concurrent map first, with minimal locking.
       InjectionMetadata metadata = this.injectionMetadataCache.get(cacheKey);
       if (InjectionMetadata.needsRefresh(metadata, clazz)) {
          synchronized (this.injectionMetadataCache) {
             metadata = this.injectionMetadataCache.get(cacheKey);
             if (InjectionMetadata.needsRefresh(metadata, clazz)) {
                if (metadata != null) {
                   metadata.clear(pvs);
                }//下面是分析当前类方法或者属性有没有标注@Autowired等自动赋值的注解
                metadata = buildAutowiringMetadata(clazz);
                this.injectionMetadataCache.put(cacheKey, metadata);
             }
          }
       }
       return metadata;
    }

	private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) {
		if (!AnnotationUtils.isCandidateClass(clazz, this.autowiredAnnotationTypes)) {
			return InjectionMetadata.EMPTY;
		}

		List<InjectionMetadata.InjectedElement> elements = new ArrayList<>();
		Class<?> targetClass = clazz;

		do {
			final List<InjectionMetadata.InjectedElement> currElements = new ArrayList<>();
            //找所有属性中标注了@Autowired\@Value\@Inject注解
			ReflectionUtils.doWithLocalFields(targetClass, field -> {
				MergedAnnotation<?> ann = findAutowiredAnnotation(field);
				if (ann != null) {
					if (Modifier.isStatic(field.getModifiers())) {
						if (logger.isInfoEnabled()) {
							logger.info("Autowired annotation is not supported on static fields: " + field);
						}
						return;
					}
					boolean required = determineRequiredStatus(ann);
					currElements.add(new AutowiredFieldElement(field, required));
				}
			});
			//拿到所有方法，看有没有@Autowired注解
			ReflectionUtils.doWithLocalMethods(targetClass, method -> {
				Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
				if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) {
					return;
				}
				MergedAnnotation<?> ann = findAutowiredAnnotation(bridgedMethod);
				if (ann != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) {
					if (Modifier.isStatic(method.getModifiers())) {
						if (logger.isInfoEnabled()) {
							logger.info("Autowired annotation is not supported on static methods: " + method);
						}
						return;
					}
					if (method.getParameterCount() == 0) {
						if (logger.isInfoEnabled()) {
							logger.info("Autowired annotation should only be used on methods with parameters: " +
									method);
						}
					}
					boolean required = determineRequiredStatus(ann);
					PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz);
					currElements.add(new AutowiredMethodElement(method, required, pd));
				}
			});

			elements.addAll(0, currElements);
			targetClass = targetClass.getSuperclass();
		}
		while (targetClass != null && targetClass != Object.class);

		return InjectionMetadata.forElements(elements, clazz);
	}

BeanUtils：Bean反射工具类

ReflectionUtils：真正操作反射的工具类

    @Nullable
    private MergedAnnotation<?> findAutowiredAnnotation(AccessibleObject ao) {
       MergedAnnotations annotations = MergedAnnotations.from(ao);
       for (Class<? extends Annotation> type : this.autowiredAnnotationTypes) {
          MergedAnnotation<?> annotation = annotations.get(type);
          if (annotation.isPresent()) {
             return annotation;
          }
       }
       return null;
    }

	private final Set<Class<? extends Annotation>> autowiredAnnotationTypes = new LinkedHashSet<>(4);

	public AutowiredAnnotationBeanPostProcessor() {
		this.autowiredAnnotationTypes.add(Autowired.class);
		this.autowiredAnnotationTypes.add(Value.class);
		try {
			this.autowiredAnnotationTypes.add((Class<? extends Annotation>)
					ClassUtils.forName("javax.inject.Inject", AutowiredAnnotationBeanPostProcessor.class.getClassLoader()));
			logger.trace("JSR-330 'javax.inject.Inject' annotation found and supported for autowiring");
		}
		catch (ClassNotFoundException ex) {
			// JSR-330 API not available - simply skip.
		}
	}

InjectionMetadata#inject()

    public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
       Collection<InjectedElement> checkedElements = this.checkedElements;
       Collection<InjectedElement> elementsToIterate =
             (checkedElements != null ? checkedElements : this.injectedElements);
       if (!elementsToIterate.isEmpty()) {
          for (InjectedElement element : elementsToIterate) {
             element.inject(target, beanName, pvs);
          }
       }
    }

AutowiredAnnotationBeanPostProcessor内部类AutowiredMethodElement#inject()

    protected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
       if (checkPropertySkipping(pvs)) {
          return;
       }
       Method method = (Method) this.member;
       Object[] arguments;
       if (this.cached) {
          try {
             arguments = resolveCachedArguments(beanName);
          }
          catch (NoSuchBeanDefinitionException ex) {
             // Unexpected removal of target bean for cached argument -> re-resolve
             arguments = resolveMethodArguments(method, bean, beanName);
          }
       }
       else {
          arguments = resolveMethodArguments(method, bean, beanName);
       }
       if (arguments != null) {
          try {
             ReflectionUtils.makeAccessible(method);
             method.invoke(bean, arguments);// 这里就是反射调用setXXX了
          }
          catch (InvocationTargetException ex) {
             throw ex.getTargetException();
          }
       }
    }

BeanPostProcessor后置处理器贯穿整个Spring框架，Spring的事务，属性赋值，等等各方面都与其有着密不可分的关系，后面就开始讲BeanPostProcessor

悦读

道可道，非常道；名可名，非常名。 无名，天地之始，有名，万物之母。 故常无欲，以观其妙，常有欲，以观其徼。 此两者，同出而异名，同谓之玄，玄之又玄，众妙之门。

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