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

     context  = createApplicationContext(); 

创建上下文

protected ConfigurableApplicationContext createApplicationContext() {Class<?> contextClass = this.applicationContextClass;if (contextClass == null) {try {contextClass = Class.forName(this.webEnvironment ? DEFAULT_WEB_CONTEXT_CLASS: DEFAULT_CONTEXT_CLASS);}catch (ClassNotFoundException ex) {throw new IllegalStateException("Unable create a default ApplicationContext, "+ "please specify an ApplicationContextClass", ex);}}return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);}

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

public AnnotationConfigEmbeddedWebApplicationContext() {this.reader = new AnnotatedBeanDefinitionReader(this);this.scanner = new ClassPathBeanDefinitionScanner(this);}

实例化AnnotatedBeanDefinitionReader以及ClassPathBeanDefinitionScanner

• 实例化AnnotatedBeanDefinitionReader
  

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {this(registry, getOrCreateEnvironment(registry));}

调用

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {Assert.notNull(registry, "BeanDefinitionRegistry must not be null");Assert.notNull(environment, "Environment must not be null");this.registry = registry;this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);}

实例化 ConditionEvaluator，将其属性ConditionContextImpl赋值

AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);

实现如下：

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(BeanDefinitionRegistry registry, Object source) {DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);if (beanFactory != null) {if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);}if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());}}Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<BeanDefinitionHolder>(4);if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));}if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));}if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));}// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));}// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition();try {def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,AnnotationConfigUtils.class.getClassLoader()));}catch (ClassNotFoundException ex) {throw new IllegalStateException("Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);}def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));}return beanDefs;}

这段代码比较长，分开来分析

DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);

获取beanFactory信息

 

private static DefaultListableBeanFactory unwrapDefaultListableBeanFactory(BeanDefinitionRegistry registry) {if (registry instanceof DefaultListableBeanFactory) {return (DefaultListableBeanFactory) registry;}else if (registry instanceof GenericApplicationContext) {return ((GenericApplicationContext) registry).getDefaultListableBeanFactory();}else {return null;}}

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:

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

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

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

这段代码以及其紧跟的代码为创建若干bean，其中

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

private static BeanDefinitionHolder registerPostProcessor(BeanDefinitionRegistry registry, RootBeanDefinition definition, String beanName) {definition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);registry.registerBeanDefinition(beanName, definition);return new BeanDefinitionHolder(definition, beanName);}

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

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)throws BeanDefinitionStoreException {this.beanFactory.registerBeanDefinition(beanName, beanDefinition);}

其中this.beanFactory为DefaultListableBeanFactory实例

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 oldBeanDefinition;oldBeanDefinition = this.beanDefinitionMap.get(beanName);if (oldBeanDefinition != null) {if (!isAllowBeanDefinitionOverriding()) {throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +"': There is already [" + oldBeanDefinition + "] bound.");}else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTUREif (this.logger.isWarnEnabled()) {this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +"' with a framework-generated bean definition: replacing [" +oldBeanDefinition + "] with [" + beanDefinition + "]");}}else {if (this.logger.isInfoEnabled()) {this.logger.info("Overriding bean definition for bean '" + beanName +"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");}}}else {this.beanDefinitionNames.add(beanName);this.manualSingletonNames.remove(beanName);this.frozenBeanDefinitionNames = null;}this.beanDefinitionMap.put(beanName, beanDefinition);if (oldBeanDefinition != null || containsSingleton(beanName)) {resetBeanDefinition(beanName);}}

以上方法完成了bean的注册；

首先完成校验

((AbstractBeanDefinition) beanDefinition).validate();

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

<span style="white-space:pre"></span>this.beanDefinitionNames.add(beanName);this.manualSingletonNames.remove(beanName);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

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) {this(registry, useDefaultFilters, getOrCreateEnvironment(registry));}

调用

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters, Environment environment) {super(useDefaultFilters, environment);Assert.notNull(registry, "BeanDefinitionRegistry must not be null");this.registry = registry;// Determine ResourceLoader to use.if (this.registry instanceof ResourceLoader) {setResourceLoader((ResourceLoader) this.registry);}}

调用super构造

 

public ClassPathScanningCandidateComponentProvider(boolean useDefaultFilters, Environment environment) {if (useDefaultFilters) {registerDefaultFilters();}Assert.notNull(environment, "Environment must not be null");this.environment = environment;}

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

protected void registerDefaultFilters() {this.includeFilters.add(new AnnotationTypeFilter(Component.class));ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();try {this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");}catch (ClassNotFoundException ex) {// JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.}try {this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");}catch (ClassNotFoundException ex) {// JSR-330 API not available - simply skip.}}

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

setResourceLoader((ResourceLoader) this.registry)

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

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。

转载请注明 
http://blog.csdn.net/liaokailin/article/details/48186331

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