spring-bean解析过程

bean解析源码分析

我是将源码下载到本地，然后搭建起来。

以xml的加载为例进行分析

编写一个测试用例

public class XmlBeanFactoryTest {
	public static void main(String[] args) {
		/*ClassPathXmlApplicationContext context = new
				ClassPathXmlApplicationContext("customtag.xml");*/
		XmlBeanFactory xmlBeanFactory = new XmlBeanFactory(new ClassPathResource("spring-bean.xml"));
		TestDao testDao = xmlBeanFactory.getBean("testDao", TestDao.class);
		testDao.test();
	}
}

从构造方法来看，XmlBeanFactory 首先通过ClassPathResource类来加载路径

public ClassPathResource(String path, @Nullable ClassLoader classLoader) {
    Assert.notNull(path, "Path must not be null");
    String pathToUse = StringUtils.cleanPath(path);
    if (pathToUse.startsWith("/")) {
        pathToUse = pathToUse.substring(1);
    }
    this.path = pathToUse;
    this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
}

加载路径完成，通过XmlBeanDefinitionReader类的loadBeanDefinitions方法

public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
    super(parentBeanFactory);
    //通过loadBeanDefinitions来加载资源
    this.reader.loadBeanDefinitions(resource);
}

进入loadBeanDefinitions

@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
    //将文件转换成编码文件
    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);
    }
    //通过属性记录加载的资源
    Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
    if (currentResources == null) {
        currentResources = new HashSet<>(4);
        this.resourcesCurrentlyBeingLoaded.set(currentResources);
    }
    if (!currentResources.add(encodedResource)) {
        throw new BeanDefinitionStoreException(
            "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
    }
    try {
        //从encodedResource中获取已经封装Resource对象，并且再次从Resource对象中获取InputStream流
        InputStream inputStream = encodedResource.getResource().getInputStream();
        try {
            //InputSource 这个类并不米自于 Spring ，它的全路径是org.xml.sax.InputSource
            InputSource inputSource = new InputSource(inputStream);
            if (encodedResource.getEncoding() != null) {
                inputSource.setEncoding(encodedResource.getEncoding());
            }
            //进入核心
            return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
        }
        finally {
            inputStream.close();
        }
    }
    catch (IOException ex) {
        throw new BeanDefinitionStoreException(
            "IOException parsing XML document from " + encodedResource.getResource(), ex);
    }
    finally {
        currentResources.remove(encodedResource);
        if (currentResources.isEmpty()) {
            this.resourcesCurrentlyBeingLoaded.remove();
        }
    }
}

进入doLoadBeanDefinitions方法，里面主要是包含doLoadDocument（）和registerBeanDefinitions（）两个方法

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

    try {
        //加载xml文件，对应到Document
        Document doc = doLoadDocument(inputSource, resource);
        //根据返回的Document注册bean信息
        int count = registerBeanDefinitions(doc, resource);
        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);
    }
}

分析doLoadDocument()方法

DocumentLoader是一个接口，通过子类DefaultDocumentLoader来进行加载

protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
    return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
                                            getValidationModeForResource(resource), isNamespaceAware());
}

/*
*EntityResolver 通过这个类来找到对应本地的DTD或者XSD文件，不需要通过网络去进行解析
*/
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
                             ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {
	//创建一个DocumentBuilderFactory工厂
    DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
    if (logger.isTraceEnabled()) {
        logger.trace("Using JAXP provider [" + factory.getClass().getName() + "]");
    }
    //
    DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
    //放回一个Document对象
    return builder.parse(inputSource);
}

registerBeanDefinitions方法

registerBeanDefinitions方法主要就是通过对应的Document进行bean的解析和注册

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    //使用defaultBeanDefinitionDocumentReader实例化BeanDefinitionDocumentReader
    BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    //获取注册前bean实例的数量
    int countBefore = getRegistry().getBeanDefinitionCount();
    //加载和注册bean实例
    documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    //返回本次加载的BeanDefinition数量
    return getRegistry().getBeanDefinitionCount() - countBefore;
}

registerBeanDefinitions方法

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
    this.readerContext = readerContext;
    doRegisterBeanDefinitions(doc.getDocumentElement());
}

protected void doRegisterBeanDefinitions(Element root) {
	//专门处理解析
    BeanDefinitionParserDelegate parent = this.delegate;
    this.delegate = createDelegate(getReaderContext(), root, parent);

    if (this.delegate.isDefaultNamespace(root)) {
        String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
        if (StringUtils.hasText(profileSpec)) {
            String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
                profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
            // We cannot use Profiles.of(...) since profile expressions are not supported
            // in XML config. See SPR-12458 for details.
            if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
                                 "] not matching: " + getReaderContext().getResource());
                }
                return;
            }
        }
    }
	//解析处理前，留给子类实现
    preProcessXml(root);
    //将xml解析成BeanDefinition
    parseBeanDefinitions(root, this.delegate);
    //解析处理后，留给子类实现
    postProcessXml(root);

    this.delegate = parent;
}

parseBeanDefinitions方法

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
    if (delegate.isDefaultNamespace(root)) {
        NodeList nl = root.getChildNodes();
        for (int i = 0; i < nl.getLength(); i++) {
            Node node = nl.item(i);
            if (node instanceof Element) {
                Element ele = (Element) node;
                //默认类型，使用默认解析
                if (delegate.isDefaultNamespace(ele)) {
                    parseDefaultElement(ele, delegate);
                }
                //自定义类型，使用自定义解析
                else {
                    delegate.parseCustomElement(ele);
                }
            }
        }
    }
    else {
        delegate.parseCustomElement(root);
    }

parseDefaultElement方法

如果是默认解析类型，使用parseDefaultElement方法进行解析，对应着四种标签类型

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
    //import标签解析和注册
    if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
        importBeanDefinitionResource(ele);
    }
    //alias别名解析和注册
    else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
        processAliasRegistration(ele);
    }
    //bean解析和注册
    else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
        processBeanDefinition(ele, delegate);
    }
    //beans解析和注册
    else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
        // recurse
        doRegisterBeanDefinitions(ele);
    }
}

默认解析（以bean标签为例）

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		//解析xml配置信息，将其加载到BeanDefinitionHolder
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			//对bean中自定义的属性进行装饰
			/*
			* <bean id="testDao" class="com.jack.TestDao">
				<mybean:user username=” aaa ”>
			* </bean>
			* */
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				//注册解析的BeanDefinition,实现在DefaultListableBeanFactory中
				BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error("Failed to register bean definition with name '" +
						bdHolder.getBeanName() + "'", ele, ex);
			}
			// Send registration event.
			//通知监听器解析和注册完成
			getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
		}
	}

解析xml将返回BeanDefinitionHolder

//解析xml配置信息，将其加载到BeanDefinitionHolder
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;
		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);
		}
		//解析xml
		AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
		if (beanDefinition != null) {
			if (!StringUtils.hasText(beanName)) {
				try {
					if (containingBean != null) {
						beanName = BeanDefinitionReaderUtils.generateBeanName(
								beanDefinition, this.readerContext.getRegistry(), true);
					}
					else {
						beanName = this.readerContext.generateBeanName(beanDefinition);
						// Register an alias for the plain bean class name, if still possible,
						// if the generator returned the class name plus a suffix.
						// This is expected for Spring 1.2/2.0 backwards compatibility.
						String beanClassName = beanDefinition.getBeanClassName();
						if (beanClassName != null &&
								beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
								!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
							aliases.add(beanClassName);
						}
					}
					if (logger.isTraceEnabled()) {
						logger.trace("Neither XML 'id' nor 'name' specified - " +
								"using generated bean name [" + beanName + "]");
					}
				}
				catch (Exception ex) {
					error(ex.getMessage(), ele);
					return null;
				}
			}
			String[] aliasesArray = StringUtils.toStringArray(aliases);
			return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
		}

		return null;
	}

//解析元素
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 {
			//创建一个BeanDefinition
			AbstractBeanDefinition bd = createBeanDefinition(className, parent);
			//解析BeanDefinition的属性
			parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
			//添加描述
			bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
			//解析meta子元素
			parseMetaElements(ele, bd);
			//解析lookup-method子元素
			parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
			//解析repalced-method子元素
			parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
			//解析Constructor-Arg子元素 初始化
			parseConstructorArgElements(ele, bd);
			//解析子元素property 对属性初始化
			parsePropertyElements(ele, bd);
			//解析子元素qualifier
			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);
		}
		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;
	}

对bean中自定义的属性进行装饰

public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
      Element ele, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {

   BeanDefinitionHolder finalDefinition = originalDef;

   // Decorate based on custom attributes first.
   NamedNodeMap attributes = ele.getAttributes();
   for (int i = 0; i < attributes.getLength(); i++) {
      Node node = attributes.item(i);
      finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
   }

   // Decorate based on custom nested elements.
   NodeList children = ele.getChildNodes();
   for (int i = 0; i < children.getLength(); i++) {
      Node node = children.item(i);
      if (node.getNodeType() == Node.ELEMENT_NODE) {
         finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
      }
   }
   return finalDefinition;
}

注册bean

public static void registerBeanDefinition(
      BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
      throws BeanDefinitionStoreException {

   // Register bean definition under primary name.
   //通过beanName作为唯一来进行注册
   String beanName = definitionHolder.getBeanName();
   registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

   // Register aliases for bean name, if any.
   //通过别名来进行注册
   String[] aliases = definitionHolder.getAliases();
   if (aliases != null) {
      for (String alias : aliases) {
         registry.registerAlias(beanName, alias);
      }
   }
}

注册bean是在DefaultListableBeanFactory

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);
   if (existingDefinition != null) {
      //如果bean已经注册了，不允许被覆盖，那么抛出异常
      if (!isAllowBeanDefinitionOverriding()) {
         throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
      }
      else if (existingDefinition.getRole() < beanDefinition.getRole()) {
         // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
         if (logger.isInfoEnabled()) {
            logger.info("Overriding user-defined bean definition for bean '" + beanName +
                  "' with a framework-generated bean definition: replacing [" +
                  existingDefinition + "] with [" + beanDefinition + "]");
         }
      }
      else if (!beanDefinition.equals(existingDefinition)) {
         if (logger.isDebugEnabled()) {
            logger.debug("Overriding bean definition for bean '" + beanName +
                  "' with a different definition: replacing [" + existingDefinition +
                  "] with [" + beanDefinition + "]");
         }
      }
      else {
         if (logger.isTraceEnabled()) {
            logger.trace("Overriding bean definition for bean '" + beanName +
                  "' with an equivalent definition: replacing [" + existingDefinition +
                  "] with [" + beanDefinition + "]");
         }
      }
      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);
            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
         //注册bean
         this.beanDefinitionMap.put(beanName, beanDefinition);
         //记录bean
         this.beanDefinitionNames.add(beanName);
         //更新单例工厂集合
         removeManualSingletonName(beanName);
      }
      this.frozenBeanDefinitionNames = null;
   }

   if (existingDefinition != null || containsSingleton(beanName)) {
      //重置所有bean对应的缓存
      resetBeanDefinition(beanName);
   }
   else if (isConfigurationFrozen()) {
      clearByTypeCache();
   }
}

通知监听器解析和注册完成

//这个是一个空实现，可以由开发人员来进行实现
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));

自定义解析

public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
   String namespaceUri = getNamespaceURI(ele);
   if (namespaceUri == null) {
      return null;
   }
    //根据用户自定义uri来获取handler
   NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
   if (handler == null) {
      error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
      return null;
   }
   return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}