這一章我們來分析Spring是如何解析<bena></bean>生成BeanDefinition的，進入

 //org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader
 1     private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
 2         if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
 3             importBeanDefinitionResource(ele);//<import/>
 
 4         }
 5         else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
 6             processAliasRegistration(ele);//<alias/>
 7         }
 8         else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
 9             processBeanDefinition(ele, delegate);//<bean/>
10         }
11         else
 
 if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
12             // recurse
13             doRegisterBeanDefinitions(ele);//嵌套的<beans/>
14         }
15     }

第9行，解析<bean/>節點，進入processBeanDefinition方法

 //org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader
 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     }

第6行，創建了BeanDefinitionHolder實例（此實例包含了BeanDefinition、BeanName、Bean的別名）
第11行，註冊BeanDefinition，其中getReaderContext()得到是在XmlBeanDefinitionReader通過createReaderContext方法創建的XmlReaderContext實例。getReaderContext().getRegistry()調用是XmlBeanDefinitionReader實例的getRegistry()，得到是BeanDefinitionRegistry實例（實現類DefaultListableBeanFactory）

//org.springframework.beans.factory.xml.XmlBeanDefinitionReader
1     /**
2      * Create the {@link XmlReaderContext} to pass over to the document reader.
3      */
4     public XmlReaderContext createReaderContext(Resource resource) {
5         return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
6                 this.sourceExtractor, this, getNamespaceHandlerResolver());
7     }

進入registerBeanDefinition方法

 //org.springframework.beans.factory.support.BeanDefinitionReaderUtils
 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 aliase : aliases) {
19                 registry.registerAlias(beanName, aliase);
20             }
21         }
22     }

第12行，獲取beanName

第13行，調用BeanDefinitionRegistry（實現類是DefaultListableBeanFactory）的registerBeanDefinition方法註冊BeanDefinition，進入方法

 //org.springframework.beans.factory.support.DefaultListableBeanFactory
 1     //---------------------------------------------------------------------
 2     // Implementation of BeanDefinitionRegistry interface
 3     //---------------------------------------------------------------------
 4 
 5     @Override
 6     public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
 7             throws BeanDefinitionStoreException {
 8 
 9         Assert.hasText(beanName, "Bean name must not be empty");
10         Assert.notNull(beanDefinition, "BeanDefinition must not be null");
11 
12         if (beanDefinition instanceof AbstractBeanDefinition) {
13             try {
14                 ((AbstractBeanDefinition) beanDefinition).validate();
15             }
16             catch (BeanDefinitionValidationException ex) {
17                 throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
18                         "Validation of bean definition failed", ex);
19             }
20         }
21 
22         synchronized (this.beanDefinitionMap) {
23             BeanDefinition oldBeanDefinition = this.beanDefinitionMap.get(beanName);
24             if (oldBeanDefinition != null) {
25                 if (!this.allowBeanDefinitionOverriding) {
26                     throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
27                             "Cannot register bean definition [" + beanDefinition + "] for bean ‘" + beanName +
28                             "‘: There is already [" + oldBeanDefinition + "] bound.");
29                 }
30                 else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
31                     // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
32                     if (this.logger.isWarnEnabled()) {
33                         this.logger.warn("Overriding user-defined bean definition for bean ‘" + beanName +
34                                 " with a framework-generated bean definition ‘: replacing [" +
35                                 oldBeanDefinition + "] with [" + beanDefinition + "]");
36                     }
37                 }
38                 else {
39                     if (this.logger.isInfoEnabled()) {
40                         this.logger.info("Overriding bean definition for bean ‘" + beanName +
41                                 "‘: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
42                     }
43                 }
44             }
45             else {
46                 this.beanDefinitionNames.add(beanName);
47                 this.frozenBeanDefinitionNames = null;
48             }
49             this.beanDefinitionMap.put(beanName, beanDefinition);
50         }
51 
52         resetBeanDefinition(beanName);
53     }

第46行，把beanName加入beanDefinitionNames（List<String>類型）

第49行，把beanName、beanDefinition按照Key-Value鍵值對放入beanDefinitionMap（Map<String, BeanDefinition>類型）

通過上面分析，我們已經可以得到所有的beanName和beanDefinition,那麽什麽時候創建bean的實例呢，下一章再進行介紹。

Spring 源碼解析（五）解析<bean></bean>