Spring 5 原始碼決議- XML中Bean配置加載-有解無憂

spring-framework 加載組態檔程序：

根據業務系統運行的環境，選擇 ApplicationContext 介面合適的實作類，啟動系統先初始化背景關系環境，然后通過BeanDefinitionReader 的實作類讀取Bean的組態檔，這里組態檔可以是 xml檔案，properties檔案，yml檔案等，也可以是注解形式掃描配置，組態檔讀取成功后，將相應的配置轉換成 BeanDefinition 的物件實體保存在DefaultListableBeanFactory#beanDefinitionMap 中，緊接著，根據配置的 BeanFactoryPostProcessor 物件串列，進行 BeanDefinition 的擴展處理，( 例如 org.springframework.beans.factory.config.PlaceholderConfigurerSupport: ${} 配置轉換成實際的值實作類，org.springframework.beans.factory.config.PropertyOverrideConfigurer: 將 beanName.property 替換成實際的值， )

--> xml配置

ApplicationContext ---> BeanDefinitionReader -+----> yml配置 -----> BeanDefinition ---> DefaultListableBeanFactory ---> BeanFactoryPostProcessor

--> Annotation 掃描

這里以 XML 配置的BeanDefinition 進行原始碼加載分析：

一. BeanFactory 實體的創建

在 AbstractApplicationContext#obtainFreshBeanFactory 方法中，是進行 bean 處理的入口，

AbstractApplicationContext#obtainFreshBeanFactory

-> AbstractRefreshableApplicationContext#refreshBeanFactory

1.檢測是否已經創建 BeanFactory ，如果創建了則銷毀BeanFactory 相關的屬性，

2.創建 BeanFactory 介面的默認實作類 DefaultListableBeanFactory 實體，

3.客戶化 BeanFactory 處理，

4.加載 BeanDefinition 定義資訊，

 1     /**
 2      * This implementation performs an actual refresh of this context's underlying
 3      * bean factory, shutting down the previous bean factory (if any) and
 4      * initializing a fresh bean factory for the next phase of the context's lifecycle.
 5      */
 6     @Override
 7     protected final void refreshBeanFactory() throws BeansException {
 8         if (hasBeanFactory()) {
 9             destroyBeans();
10             closeBeanFactory();
11         }
12         try {
13             DefaultListableBeanFactory beanFactory = createBeanFactory();
14             beanFactory.setSerializationId(getId());
15             customizeBeanFactory(beanFactory);
16             loadBeanDefinitions(beanFactory);
17             this.beanFactory = beanFactory;
18         }
19         catch (IOException ex) {
20             throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
21         }
22     }

二. ApplicationContex 讀取 BeanDefinition 的加載分析

這里我們分析 XML 形式配置的加載，因此通過 AbstractXmlApplicationContext 來分析原始碼，

AbstractApplicationContext#obtainFreshBeanFactory

-> AbstractRefreshableApplicationContext#refreshBeanFactory

--> AbstractXmlApplicationContext#loadBeanDefinitions(DefaultListableBeanFactory)

1.首先創建讀取 BeanDefinition 的 BeanDefinitionReader 介面實作 XmlBeanDefinitionReader 實體，并設定環境資訊，

2.通過 BeanDefinitionReader 實作讀取 BeanDefinition 配置資訊，

 1     /**
 2      * Loads the bean definitions via an XmlBeanDefinitionReader.
 3      * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 4      * @see #initBeanDefinitionReader
 5      * @see #loadBeanDefinitions
 6      */
 7     @Override
 8     protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
 9         // Create a new XmlBeanDefinitionReader for the given BeanFactory.
10         XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
11 
12         // Configure the bean definition reader with this context's
13         // resource loading environment.
14         beanDefinitionReader.setEnvironment(this.getEnvironment());
15         beanDefinitionReader.setResourceLoader(this);
16         beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
17 
18         // Allow a subclass to provide custom initialization of the reader,
19         // then proceed with actually loading the bean definitions.
20         initBeanDefinitionReader(beanDefinitionReader);
21         loadBeanDefinitions(beanDefinitionReader);
22     }

三. BeanDefinitionReader 讀取，加載 BeanDefinition 配置分析

AbstractXmlApplicationContext#loadBeanDefinitions(DefaultListableBeanFactory)

--> AbstractXmlApplicationContext#loadBeanDefinitions(XmlBeanDefinitionReader)

--> AbstractBeanDefinitionReader#loadBeanDefinitions(String, Set<Resource>)

--> XmlBeanDefinitionReader#loadBeanDefinitions(EncodedResource)

--> XmlBeanDefinitionReader#doLoadBeanDefinitions(InputSource, Resource )

1.讀取 XML 檔案，獲取到 Document 實體，為后續決議配置做準備，

2.向 BeanFactory 中注冊 BeanDefinition 配置資訊，

此處例外捕獲比較多，學習例外規范處理，最底層的 Throwable 例外也捕獲了，保證程式不會例外退出，

 1     /**
 2      * Actually load bean definitions from the specified XML file.
 3      * @param inputSource the SAX InputSource to read from
 4      * @param resource the resource descriptor for the XML file
 5      * @return the number of bean definitions found
 6      * @throws BeanDefinitionStoreException in case of loading or parsing errors
 7      * @see #doLoadDocument
 8      * @see #registerBeanDefinitions
 9      */
10     protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
11             throws BeanDefinitionStoreException {
12 
13         try {
14             Document doc = doLoadDocument(inputSource, resource);
15             int count = registerBeanDefinitions(doc, resource);
16             if (logger.isDebugEnabled()) {
17                 logger.debug("Loaded " + count + " bean definitions from " + resource);
18             }
19             return count;
20         }
21         catch (BeanDefinitionStoreException ex) {
22             throw ex;
23         }
24         catch (SAXParseException ex) {
25             throw new XmlBeanDefinitionStoreException(resource.getDescription(),
26                     "Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
27         }
28         catch (SAXException ex) {
29             throw new XmlBeanDefinitionStoreException(resource.getDescription(),
30                     "XML document from " + resource + " is invalid", ex);
31         }
32         catch (ParserConfigurationException ex) {
33             throw new BeanDefinitionStoreException(resource.getDescription(),
34                     "Parser configuration exception parsing XML from " + resource, ex);
35         }
36         catch (IOException ex) {
37             throw new BeanDefinitionStoreException(resource.getDescription(),
38                     "IOException parsing XML document from " + resource, ex);
39         }
40         catch (Throwable ex) {
41             throw new BeanDefinitionStoreException(resource.getDescription(),
42                     "Unexpected exception parsing XML document from " + resource, ex);
43         }
44     }

四.BeanDefinitionDocumentReader 決議 BeanDefinition 配置分析

(一） BeanDefinitionDocumentReader 分析

XmlBeanDefinitionReader#doLoadBeanDefinitions

--> XmlBeanDefinitionReader#registerBeanDefinitions(Document, Resource)

--> BeanDefinitionDocumentReader#registerBeanDefinitionsregisterBeanDefinitions(Document, XmlReaderContext)

1. 創建 BeanDefinitionDocumentReader 物件實體，

2.創建讀取 BeanDefinition 配置資訊Document的背景關系(XmlReaderContext)，為后續決議配置提供相關支持，

3. 決議并注冊Document 中配置的 BeanDefinition 資訊，在 DefaultBeanDefinitionDocumentReader 實作具體邏輯，

 1     /**
 2      * Register the bean definitions contained in the given DOM document.
 3      * Called by {@code loadBeanDefinitions}.
 4      * <p>Creates a new instance of the parser class and invokes
 5      * {@code registerBeanDefinitions} on it.
 6      * @param doc the DOM document
 7      * @param resource the resource descriptor (for context information)
 8      * @return the number of bean definitions found
 9      * @throws BeanDefinitionStoreException in case of parsing errors
10      * @see #loadBeanDefinitions
11      * @see #setDocumentReaderClass
12      * @see BeanDefinitionDocumentReader#registerBeanDefinitions
13      */
14     public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
15         BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
16         int countBefore = getRegistry().getBeanDefinitionCount();
17         documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
18         return getRegistry().getBeanDefinitionCount() - countBefore;
19     }

(二）BeanDefinitionDocumentReader 實作類 DefaultBeanDefinitionDocumentReader分析

BeanDefinitionDocumentReader#registerBeanDefinitionsregisterBeanDefinitions(Document, XmlReaderContext)

--> DefaultBeanDefinitionDocumentReader#registerBeanDefinitions(Document doc, XmlReaderContext readerContext)

--> DefaultBeanDefinitionDocumentReader#doRegisterBeanDefinitions(Element)

1. 根據 ReaderContext 資訊，創建對應的實體，

2. 檢查 profile 配置資訊，如果不匹配，則不決議當前root節點下的 BeanDefinition 配置，

3. 當前root節點前置處理，

4. 決議當前 root 節點的 BeanDefinition 配置資訊，

5. 當前root節點后置處理，

（三) DefaultBeanDefinitionDocumentReader#parseBeanDefinitions 分析

DefaultBeanDefinitionDocumentReader#parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate)

--> DefaultBeanDefinitionDocumentReader#parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate)

--> BeanDefinitionParserDelegate#parseCustomElement(Element)

1. 判斷 root 節點 DefaultNamespace 是否是 http://www.springframework.org/schema/beans ，

如果是，則遍歷子節點進行決議，

當子節點是 DefaultNamespace ，則使用 DefaultBeanDefinitionDocumentReader#parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) 決議節點，

否做使用 BeanDefinitionParserDelegate#parseCustomElement(Element) 決議節點，

2. 非默認 DefaultNamespace 值，則使用 BeanDefinitionParserDelegate#parseCustomElement(Element) 決議節點，

例如 AOP 配置節點決議，例如：<aop:config>

事物配置節點決議，例如：<tx:annotation-driven proxy-target- />

(四) 決議 DefaultNamespace 節點 BeanDefinition 資訊，

DefaultBeanDefinitionDocumentReader#parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate)

--> DefaultBeanDefinitionDocumentReader#importBeanDefinitionResource(Element)

--> DefaultBeanDefinitionDocumentReader#processAliasRegistration(Element)

--> DefaultBeanDefinitionDocumentReader#processBeanDefinition(Element, BeanDefinitionParserDelegate)

--> DefaultBeanDefinitionDocumentReader#doRegisterBeanDefinitions(Element)

1.依次決議 import 節點，alias 節點，bean節點， beans節點定義的 BeanDefinition 資訊，

（五）決議非默認命名空間節點 BeanDefinition 資訊，

BeanDefinitionParserDelegate#parseCustomElement(Element)

--> BeanDefinitionParserDelegate#parseCustomElement(Element, BeanDefinition)

1.獲取節點命名空間，

2.根據命名空間獲取對應的決議器，

3. 決議節點 BeanDefinition 資訊，

 1     /**
 2      * Parse a custom element (outside of the default namespace).
 3      * @param ele the element to parse
 4      * @param containingBd the containing bean definition (if any)
 5      * @return the resulting bean definition
 6      */
 7     @Nullable
 8     public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
 9         String namespaceUri = getNamespaceURI(ele);
10         if (namespaceUri == null) {
11             return null;
12         }
13         NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
14         if (handler == null) {
15             error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
16             return null;
17         }
18         return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
19     }

五.BeanDefinitionDocumentReader 決議 bean 節點

XmlBeanDefinitionReader#loadBeanDefinitions(EncodedResource)

--> XmlBeanDefinitionReader#doLoadBeanDefinitions(InputSource, Resource)

--> XmlBeanDefinitionReader#registerBeanDefinitions(Document, Resource)

--> DefaultBeanDefinitionDocumentReader#registerBeanDefinitions(Document, XmlReaderContext)

--> DefaultBeanDefinitionDocumentReader#doRegisterBeanDefinitions(Element)

--> DefaultBeanDefinitionDocumentReader#parseBeanDefinitions(Element , BeanDefinitionParserDelegate)

--> DefaultBeanDefinitionDocumentReader#parseDefaultElement(Element, BeanDefinitionParserDelegate)

--> DefaultBeanDefinitionDocumentReader#processBeanDefinition(Element, BeanDefinitionParserDelegate)

1.使用 BeanDefinitionParserDelegate 決議 Bean 配置節點，得到保存 BeanDefinition 資訊的輔助物件 BeanDefinitionHolder 實體，

2.當決議的 Bean 配置 BeanDefinitionHolder 實體不為空，則進行 Bean 配置后續處理，

a. 當 Bean 配置節點找到其他 Namespace 對應處理器(NamespaceHandler),則進行特殊化處理，

b. 向 BeanFactory 中注冊決議成功的 BeanDefinition 定義，

c.發送 BeanDefinition 決議成功事件 BeanComponentDefinition，

 1     /**
 2      * Process the given bean element, parsing the bean definition
 3      * and registering it with the registry.
 4      */
 5     protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
 6         BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
 7         if (bdHolder != null) {
 8             bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
 9             try {
10                 // Register the final decorated instance.
11                 BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
12             }
13             catch (BeanDefinitionStoreException ex) {
14                 getReaderContext().error("Failed to register bean definition with name '" +
15                         bdHolder.getBeanName() + "'", ele, ex);
16             }
17             // Send registration event.
18             getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
19         }
20     }

六. BeanDefinitionParserDelegate#parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition) 決議 bean 節點

DefaultBeanDefinitionDocumentReader#processBeanDefinition(Element, BeanDefinitionParserDelegate)

--> BeanDefinitionParserDelegate#parseBeanDefinitionElement(Element)

--> BeanDefinitionParserDelegate#parseBeanDefinitionElement(Element, BeanDefinition)

1.決議 Element 元素的 id 和 name 屬性，得到 beanName 和 aliases，

2.檢查 beanName 是否唯一，

3. 創建 AbstractBeanDefinition 物件實體 bd ，并通過依次決議 Element 元素的屬性給 bd 賦值，

依次決議子節點 meta， lookup-method, replaced-method, constructor-arg, property, qualifier,并將決議后的值添加到 bd 相關變數，

設定 bd 解析資源的相關資訊，

4. 如果 3 決議失敗，則回傳的實體BeanDefinition 為 null，則這里也直接回傳，

5. 當上述步驟決議的 beanName 為空時，使用指定方式生成 beanName，

當前 bean 是在其他Bean 內部時，使用BeanDefinitionReaderUtils#generateBeanName(BeanDefinition, BeanDefinitionRegistry, boolean) 生成 beanName，

否則使用 XmlReaderContext 對應生成器生成 beanName，

6.根據決議的 BeanDefinition 創建對應的 BeanDefinitionHolder 物件實體，

在決議 bean 配置資訊時，主要有如下七個元資料包裝類，對相關屬性配置進行歸檔：

org.springframework.beans.factory.config.ConstructorArgumentValues <constructor-arg>

org.springframework.beans.PropertyValue <property>

org.springframework.beans.factory.support.ManagedArray <array>

org.springframework.beans.factory.support.ManagedList <list>

org.springframework.beans.factory.support.ManagedSet <set>

org.springframework.beans.factory.support.ManagedMap <map>

org.springframework.beans.factory.support.ManagedProperties <props>

每個配置具體字串值對應了如下三種處理型別：

org.springframework.beans.factory.config.TypedStringValue <value>

org.springframework.beans.factory.config.RuntimeBeanReference <ref>

org.springframework.beans.factory.config.RuntimeBeanNameReference <idref>

 1     /**
 2      * Parses the supplied {@code <bean>} element. May return {@code null}
 3      * if there were errors during parse. Errors are reported to the
 4      * {@link org.springframework.beans.factory.parsing.ProblemReporter}.
 5      */
 6     @Nullable
 7     public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
 8         String id = ele.getAttribute(ID_ATTRIBUTE);
 9         String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
10 
11         List<String> aliases = new ArrayList<>();
12         if (StringUtils.hasLength(nameAttr)) {
13             String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
14             aliases.addAll(Arrays.asList(nameArr));
15         }
16 
17         String beanName = id;
18         if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
19             beanName = aliases.remove(0);
20             if (logger.isTraceEnabled()) {
21                 logger.trace("No XML 'id' specified - using '" + beanName +
22                         "' as bean name and " + aliases + " as aliases");
23             }
24         }
25 
26         if (containingBean == null) {
27             checkNameUniqueness(beanName, aliases, ele);
28         }
29 
30         AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
31         if (beanDefinition != null) {
32             if (!StringUtils.hasText(beanName)) {
33                 try {
34                     if (containingBean != null) {
35                         beanName = BeanDefinitionReaderUtils.generateBeanName(
36                                 beanDefinition, this.readerContext.getRegistry(), true);
37                     }
38                     else {
39                         beanName = this.readerContext.generateBeanName(beanDefinition);
40                         // Register an alias for the plain bean class name, if still possible,
41                         // if the generator returned the class name plus a suffix.
42                         // This is expected for Spring 1.2/2.0 backwards compatibility.
43                         String beanClassName = beanDefinition.getBeanClassName();
44                         if (beanClassName != null &&
45                                 beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
46                                 !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
47                             aliases.add(beanClassName);
48                         }
49                     }
50                     if (logger.isTraceEnabled()) {
51                         logger.trace("Neither XML 'id' nor 'name' specified - " +
52                                 "using generated bean name [" + beanName + "]");
53                     }
54                 }
55                 catch (Exception ex) {
56                     error(ex.getMessage(), ele);
57                     return null;
58                 }
59             }
60             String[] aliasesArray = StringUtils.toStringArray(aliases);
61             return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
62         }
63 
64         return null;
65     }

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七. BeanDefinitionParserDelegate#decorateIfRequired(Node, BeanDefinitionHolder, @Nullable BeanDefinition)決議 bean 節點自定義屬性

DefaultBeanDefinitionDocumentReader#processBeanDefinition(Element, BeanDefinitionParserDelegate)

--> BeanDefinitionParserDelegate#parseBeanDefinitionElement(Element)

--> BeanDefinitionParserDelegate#decorateBeanDefinitionIfRequired(Element, BeanDefinitionHolder)

--＞ BeanDefinitionParserDelegate#decorateBeanDefinitionIfRequired(Element, BeanDefinitionHolder, BeanDefinition)

--> BeanDefinitionParserDelegate#decorateIfRequired(Node, BeanDefinitionHolder, @Nullable BeanDefinition)

1. 獲得節點(Node) 的命名空間URI(NamespaceURI)，

2. 如果命名空間URI不是默認的，則進行特殊處理，

3. 通過命名空間URI 到讀取檔案背景關系(XmlReaderContext) 中查找對應處理器(NamespaceHandler)，

例如

Context的處理器： org.springframework.context.config.ContextNamespaceHandler

AOP的處理器： org.springframework.aop.config.AopNamespaceHandler

component的處理器： org.springframework.beans.factory.xml.ComponentNamespaceHandler

4. 呼叫 NamespaceHandler#decorate(Node, BeanDefinitionHolder, ParserContext)方法決議節點配置資訊，并回傳新的 BeanDefinitionHolder 實體，

 1     /**
 2      * Decorate the given bean definition through a namespace handler,
 3      * if applicable.
 4      * @param node the current child node
 5      * @param originalDef the current bean definition
 6      * @param containingBd the containing bean definition (if any)
 7      * @return the decorated bean definition
 8      */
 9     public BeanDefinitionHolder decorateIfRequired(
10             Node node, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {
11 
12         String namespaceUri = getNamespaceURI(node);
13         if (namespaceUri != null && !isDefaultNamespace(namespaceUri)) {
14             NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
15             if (handler != null) {
16                 BeanDefinitionHolder decorated =
17                         handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
18                 if (decorated != null) {
19                     return decorated;
20                 }
21             }
22             else if (namespaceUri.startsWith("http://www.springframework.org/schema/")) {
23                 error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", node);
24             }
25             else {
26                 // A custom namespace, not to be handled by Spring - maybe "xml:...".
27                 if (logger.isDebugEnabled()) {
28                     logger.debug("No Spring NamespaceHandler found for XML schema namespace [" + namespaceUri + "]");
29                 }
30             }
31         }
32         return originalDef;
33     }

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八. BeanDefinitionReaderUtils#registerBeanDefinition(BeanDefinitionHolder, BeanDefinitionRegistry) 向 BeanFactory 注冊 BeanDefinition 實體資訊

1. 通過 beanName 向 beanFactory 中注冊 BeanDefinition 實體，

2. 通過 beanName 向 beanFactory 中注冊 BeanDefinition 實體的別名串列，

 1     /**
 2      * Register the given bean definition with the given bean factory.
 3      * @param definitionHolder the bean definition including name and aliases
 4      * @param registry the bean factory to register with
 5      * @throws BeanDefinitionStoreException if registration failed
 6      */
 7     public static void registerBeanDefinition(
 8             BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
 9             throws BeanDefinitionStoreException {
10 
11         // Register bean definition under primary name.
12         String beanName = definitionHolder.getBeanName();
13         registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
14 
15         // Register aliases for bean name, if any.
16         String[] aliases = definitionHolder.getAliases();
17         if (aliases != null) {
18             for (String alias : aliases) {
19                 registry.registerAlias(beanName, alias);
20             }
21         }
22     }

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-----------------------------------------------------作者：流羽經流年看繁花似錦望星辰不變出處：https://www.cnblogs.com/StreamPlume/p/15673202.html

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