spring boot实战(第八篇)上下文的创建

前言

本篇主要讲解spring boot上下文的创建，为后续源码的解读打下铺垫

ApplicationContext

在run方法中执行

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1. context  = createApplicationContext();   

创建上下文

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1. protected ConfigurableApplicationContext createApplicationContext() {  
2.         Class<?> contextClass = this.applicationContextClass;  
3.         if (contextClass == null) {  
4.             try {  
5.                 contextClass = Class  
6.                         .forName(this.webEnvironment ? DEFAULT_WEB_CONTEXT_CLASS  
7.                                 : DEFAULT_CONTEXT_CLASS);  
8.             }  
9.             catch (ClassNotFoundException ex) {  
10.                 throw new IllegalStateException(  
11.                         "Unable create a default ApplicationContext, "  
12.                                 + "please specify an ApplicationContextClass", ex);  
13.             }  
14.         }  
15.         return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);  
16.     }  

创建DEFAULT_WEB_CONTEXT_CLASS -->AnnotationConfigEmbeddedWebApplicationContext实例，创建实例 调用构造方法，首先需要分清楚spring boot中多上下文之间的关联关系，

结构相对比较复杂一些

执行AnnotationConfigEmbeddedWebApplicationContext构造方法

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1. public AnnotationConfigEmbeddedWebApplicationContext() {  
2.         this.reader = new AnnotatedBeanDefinitionReader(this);  
3.         this.scanner = new ClassPathBeanDefinitionScanner(this);  
4.     }  

实例化AnnotatedBeanDefinitionReader以及ClassPathBeanDefinitionScanner

• 实例化AnnotatedBeanDefinitionReader
  

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1. public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {  
2.         this(registry, getOrCreateEnvironment(registry));  
3.     }  

调用

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1. public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {  
2.         Assert.notNull(registry, "BeanDefinitionRegistry must not be null");  
3.         Assert.notNull(environment, "Environment must not be null");  
4.         this.registry = registry;  
5.         this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);  
6.         AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);  
7.     }  

实例化 ConditionEvaluator，将其属性ConditionContextImpl赋值

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1. AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);  

实现如下：

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1. public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(  
2.             BeanDefinitionRegistry registry, Object source) {  
3.   
4.         DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);  
5.         if (beanFactory != null) {  
6.             if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {  
7.                 beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);  
8.             }  
9.             if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {  
10.                 beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());  
11.             }  
12.         }  
13.   
14.         Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<BeanDefinitionHolder>(4);  
15.   
16.         if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {  
17.             RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);  
18.             def.setSource(source);  
19.             beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));  
20.         }  
21.   
22.         if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {  
23.             RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);  
24.             def.setSource(source);  
25.             beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));  
26.         }  
27.   
28.         if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {  
29.             RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);  
30.             def.setSource(source);  
31.             beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));  
32.         }  
33.   
34.         // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.  
35.         if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {  
36.             RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);  
37.             def.setSource(source);  
38.             beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));  
39.         }  
40.   
41.         // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.  
42.         if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {  
43.             RootBeanDefinition def = new RootBeanDefinition();  
44.             try {  
45.                 def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,  
46.                         AnnotationConfigUtils.class.getClassLoader()));  
47.             }  
48.             catch (ClassNotFoundException ex) {  
49.                 throw new IllegalStateException(  
50.                         "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);  
51.             }  
52.             def.setSource(source);  
53.             beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));  
54.         }  
55.   
56.         return beanDefs;  
57.     }  

这段代码比较长，分开来分析

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1. DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);  

获取beanFactory信息

 

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1. private static DefaultListableBeanFactory unwrapDefaultListableBeanFactory(BeanDefinitionRegistry registry) {  
2.         if (registry instanceof DefaultListableBeanFactory) {  
3.             return (DefaultListableBeanFactory) registry;  
4.         }  
5.         else if (registry instanceof GenericApplicationContext) {  
6.             return ((GenericApplicationContext) registry).getDefaultListableBeanFactory();  
7.         }  
8.         else {  
9.             return null;  
10.         }  
11.     }  

代码执行到 registry  instanceof GenericApplicationContext(通过类继承结构可得到)，随后调用GenericApplicationContext# getDefaultListableBeanFactory()方法，GenericApplicationContext在构造方法中实例化了属性beanFactory的值

为DefaultListableBeanFactory:

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1. public GenericApplicationContext() {  
2.         this.beanFactory = new DefaultListableBeanFactory();  
3.     }  

其构造优先于AnnotationConfigEmbeddedWebApplicationContext构造方法执行。

以上获得了BeanFactory信息

BeanDefinition

在获取完BeanFactory以后，代码中涉及到了bean定义信息，首先来看下BeanDefinition相关信息

• BeanDefinition 设计bean相关信息
• BeanDefinitionHolder 封装bean定义相关信息，以及bean名称、别名等
• BeanDefinitionRegistry 持有所有注册的bean相关信息

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1. if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {  
2.             RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);  
3.             def.setSource(source);  
4.             beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));  
5.         }  

这段代码以及其紧跟的代码为创建若干bean，其中

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1. registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)  

表示注册名称为org.springframework.context.annotation.internalConfigurationAnnotationProcessor，beanClass 对应为ConfigurationClassPostProcessor的bean

Bean注册

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1. private static BeanDefinitionHolder registerPostProcessor(  
2.             BeanDefinitionRegistry registry, RootBeanDefinition definition, String beanName) {  
3.   
4.         definition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);  
5.         registry.registerBeanDefinition(beanName, definition);  
6.         return new BeanDefinitionHolder(definition, beanName);  
7.     }  

其中 registry.registerBeanDefinition( beanName, definition)调用GenericApplicationContext中的方法

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1. public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)  
2.             throws BeanDefinitionStoreException {  
3.   
4.         this.beanFactory.registerBeanDefinition(beanName, beanDefinition);  
5.     }  

其中 this .beanFactory为DefaultListableBeanFactory实例

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

以上方法完成了bean的注册；

首先完成校验

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1. ((AbstractBeanDefinition) beanDefinition).validate();  

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1. oldBeanDefinition = this.beanDefinitionMap.get(beanName);  

表示从map中获取bean，初始肯定无法获取，进入如下程序

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1. <span style="white-space:pre">            </span>this.beanDefinitionNames.add(beanName);  
2.             this.manualSingletonNames.remove(beanName);  
3.             this.frozenBeanDefinitionNames = null;<p class="p1"><span class="s1"><span style="white-space:pre">           </span>this</span><span class="s2">.</span><span class="s3">beanDefinitionMap</span><span class="s2">.put(</span>beanName<span class="s2">, </span>beanDefinition<span class="s2">);</span></p>  

完成bean信息的存储。

这里顺便解释下，在从map中获取到bean时表示bean已经注册，则会判断是否可以覆盖oldBean，也需要判断bean对应的Role级别

 以上完成了AnnotatedBeanDefinitionReader实例的构造

接下来为ClassPathBeanDefinitionScanner实例的创建

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1. public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) {  
2.         this(registry, useDefaultFilters, getOrCreateEnvironment(registry));  
3.     }  

调用

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1. public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters, Environment environment) {  
2.         super(useDefaultFilters, environment);  
3.   
4.         Assert.notNull(registry, "BeanDefinitionRegistry must not be null");  
5.         this.registry = registry;  
6.   
7.         // Determine ResourceLoader to use.  
8.         if (this.registry instanceof ResourceLoader) {  
9.             setResourceLoader((ResourceLoader) this.registry);  
10.         }  
11.     }  

调用super构造

 

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1. public ClassPathScanningCandidateComponentProvider(boolean useDefaultFilters, Environment environment) {  
2.         if (useDefaultFilters) {  
3.             registerDefaultFilters();  
4.         }  
5.         Assert.notNull(environment, "Environment must not be null");  
6.         this.environment = environment;  
7.     }  

在该方法中完成了environment的赋值以及为ClassPathScanningCandidateComponentProvider完成了默认过滤器的注册

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1. protected void registerDefaultFilters() {  
2.         this.includeFilters.add(new AnnotationTypeFilter(Component.class));  
3.         ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();  
4.         try {  
5.             this.includeFilters.add(new AnnotationTypeFilter(  
6.                     ((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));  
7.             logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");  
8.         }  
9.         catch (ClassNotFoundException ex) {  
10.             // JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.  
11.         }  
12.         try {  
13.             this.includeFilters.add(new AnnotationTypeFilter(  
14.                     ((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));  
15.             logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");  
16.         }  
17.         catch (ClassNotFoundException ex) {  
18.             // JSR-330 API not available - simply skip.  
19.         }  
20.     }  

将Component、ManagedBean、Named注解增加到包含过滤规则中。

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1. setResourceLoader((ResourceLoader) this.registry)  

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1. public void setResourceLoader(ResourceLoader resourceLoader) {  
2.         this.resourcePatternResolver = ResourcePatternUtils.getResourcePatternResolver(resourceLoader);  
3.         this.metadataReaderFactory = new CachingMetadataReaderFactory(resourceLoader);  
4.     }  

完成对 resourcePatternResolver以及 metadataReaderFactory的赋值操作。

以上完成了上下文的创建

小结

在创建上下文时 完成了BeanFactory的创建，注册了特定的bean信息，完成了各种属性变量的初始化操作，各属性值将在后续文章中依次讲述。

本文转自http://blog.csdn.net/liaokailin/article/details/48186331