1.简单的示例：

1 @Configuration2 @EnableConfigurationProperties({DemoProperties.class})3 public classDemoConfiguration {4
5 @Bean6     publicBook getBook(){7        return newBook();8 }9 }

1 @Autowired Book book;2
3 @Test4     public voidtestBook(){5 System.out.println(book.toString());6     }

结果打印出book对象，证明Book已经被注入到Spring 容器中了。

2.@Configuration配置的bean是如何注入到Spring容器中的呢？

首先先来简单介绍下通过BeanDefinitionRegistry注入bean

1 @Autowired2     public voidregistBeanDefinition(BeanFactory factory){3         if(factory instanceofBeanDefinitionRegistry) {4             BeanDefinitionRegistry registry =(BeanDefinitionRegistry)factory;5             BeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Book.class).getBeanDefinition();6             registry.registerBeanDefinition("mybook", beanDefinition);7 }8     }

1     @Autowired @Qualifier("mybook") Book book2;2 @Test3     public voidtestBook2(){4 System.out.println(book2);5     }

结果同样打印出book对象，这里，笔者将beanFactory强转为BenDefinitionRegistry,因为笔者的Demo中使用的是默认BeanFactory,----DefaultListableBeanFactory,他实现了BeanDefinitionRegistry接口。

3.入口，下图为ApplicaitonContext refresh方法的简化，只保留了BeandefinitionRegistry注册bean部分功能。

然，似乎并没什么用？此处会调用BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法。要解决的一个问题是，BeanDefinitionRegistryPostProcessor类型的bean是如何注入的。以SpringBoot初始化为例。

注意到，ApplicationContext的构造方法：

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

1 publicAnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {2         this(registry, getOrCreateEnvironment(registry));3     }

1     publicAnnotatedBeanDefinitionReader(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     }

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() instanceofAnnotationAwareOrderComparator)) {7 beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);8 }9             if (!(beanFactory.getAutowireCandidateResolver() instanceofContextAnnotationAutowireCandidateResolver)) {10                 beanFactory.setAutowireCandidateResolver(newContextAnnotationAutowireCandidateResolver());11 }12 }13
14         Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<BeanDefinitionHolder>(4);15                 //注解@Configuration处理
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         .......//省略部分代码
23
24         returnbeanDefs;25     }

注意到对@Configuration的处理为ConfigurationClassPostProcessor。

注意到ConfigurationClassPostProcessor实现了BeanDefinitionRegistryPostProcessor接口，显然关键方法为postProcessBeanDefinitionRegistry。ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry会调用ConfirgurationClassParser的parse方法。会依次解析注解，我们一步一步查看对各个注解的解析。

（1）@PropertySources和@PropertySource　　

1 @Target(ElementType.TYPE)2 @Retention(RetentionPolicy.RUNTIME)3 @Documented4 public @interfacePropertySources {5
6 PropertySource[] value();7
8 }

最终都是处理@PropertySource,@PropertySources仅仅只是包含多个@PropertySource,@PropertySource注解的主要功能是引入配置文件，将配置的属性键值对与环境变量中的配置合并。其中最关键的类为MutablePropertySources

1 public class MutablePropertySources implementsPropertySources {2
3     private finalLog logger;4
5     private final List<PropertySource<?>> propertySourceList = new CopyOnWriteArrayList<PropertySource<?>>();6 ......7 }

显然MutablePropertySources中包含有一个PropertySource列表。MutablePropertySources仅仅是封装了迭代器功能。可以理解成PropertySources是PropertySource的集合，增加了常用的集合操作。

（2）@ComponentScan

定义自动扫描的包。简化的序列图如下：

其最关键的方法为doScan方法，会注册BeanDefinition到容器中。

1     protected Set<BeanDefinitionHolder>doScan(String... basePackages) {2         Assert.notEmpty(basePackages, "At least one base package must be specified");3         Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();4         for(String basePackage : basePackages) {5             Set<BeanDefinition> candidates =findCandidateComponents(basePackage);6             for(BeanDefinition candidate : candidates) {7                 ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);8 candidate.setScope(scopeMetadata.getScopeName());9                 String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);10                 if (candidate instanceofAbstractBeanDefinition) {11 postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);12 }13                 if (candidate instanceofAnnotatedBeanDefinition) {14 AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);15 }16                 if(checkCandidate(beanName, candidate)) {17                     BeanDefinitionHolder definitionHolder = newBeanDefinitionHolder(candidate, beanName);18                     definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);19 beanDefinitions.add(definitionHolder);20                     registerBeanDefinition(definitionHolder, this.registry);21 }22 }23 }24         returnbeanDefinitions;25     }

registerBeanDefinition(definitionHolder, this.registry);能说明一切。

（3）@Import

@Import注解可以配置需要引入的class(假设配置为A,可以是数组),有三种方式。其流程图如下：

如果A为ImportSelector的子类，调用selectImports()方法，返回class类名数组，循环解析每一个import的类，如果A为BeanDefinitionRegistrar则直接调用registerBeanDefinition直接注入bean到容器中。如果A为普通的类（非前面提到的两种类型），则将A当做@Configuration配置的类，重新解析Configuration.

（4）@ImportSource

主要功能为引入资源文件。

（5）@Bean，比较简单，童FactoryMethod一样

1         //Process individual @Bean methods
2         Set<MethodMetadata> beanMethods = sourceClass.getMetadata().getAnnotatedMethods(Bean.class.getName());3         for(MethodMetadata methodMetadata : beanMethods) {4             configClass.addBeanMethod(newBeanMethod(methodMetadata, configClass));5 }6
7         //Process default methods on interfaces
8         for(SourceClass ifc : sourceClass.getInterfaces()) {9             beanMethods = ifc.getMetadata().getAnnotatedMethods(Bean.class.getName());10             for(MethodMetadata methodMetadata : beanMethods) {11                 if (!methodMetadata.isAbstract()) {12                     //A default method or other concrete method on a Java 8+ interface...
13                     configClass.addBeanMethod(newBeanMethod(methodMetadata, configClass));14 }15 }16         }

最后真实加载beanDefinition是loadBeanDefinitionsForConfigurationClass方法：

1     private voidloadBeanDefinitionsForConfigurationClass(ConfigurationClass configClass,2 TrackedConditionEvaluator trackedConditionEvaluator) {3
4         if(trackedConditionEvaluator.shouldSkip(configClass)) {5             String beanName =configClass.getBeanName();6             if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {7                 this.registry.removeBeanDefinition(beanName);8 }9             this.importRegistry.removeImportingClassFor(configClass.getMetadata().getClassName());10             return;11 }12
13         if(configClass.isImported()) {14 registerBeanDefinitionForImportedConfigurationClass(configClass);15 }16         for(BeanMethod beanMethod : configClass.getBeanMethods()) {17 loadBeanDefinitionsForBeanMethod(beanMethod);18 }19 loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());20 loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());21     }