@param注解的用法解析_SpringBoot 配置类解析

// 通常一个SpringBoot工程会含有这样一个主配置类,它位于我们项目的根包下,通过启动这个main方法就可以启动我们的项目
// 下面我们先分析@SpringBootApplication注解有哪些作用,在第二节中分析run方法,在run方法中会进行配置类的解析
@SpringBootApplication
public class SpringbootApplication {
    public static void main(String[] args) {
       SpringApplication.run(SpringbootApplication.class, args);
    }
}

// 点击@SpringBootApplication进去发现它其实是由三个核心注解构成的,下面分别讲解这三个注解
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
                      @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

// 点进去发现它其实就是一个@Configuration注解,SpringBoot解析到就会知道这是一个配置类,会给容器中引入一些bean
// 一个被@Configuration标注的类,相当于一个applicationContext.xml文件
// @Configuration点进去发现其实就是一个@Component注解
@Configuration
public @interface SpringBootConfiguration {
 
}

// 结合下面@AutoConfigurationPackage注解,发现@EnableAutoConfiguration注解就是通过@Import注解给容器中引入了两个bean,
// 分别是AutoConfigurationImportSelector和AutoConfigurationPackages.Registrar,通过这两个类可以给容器中引入更多的类
// 下面先介绍下@Import注解的使用
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
}
 
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {
}

// 步骤1) 
// 创建几个动物的实体类,如Cat、Bird、Chicken、Dog、Duck、Pig、Sheep、Snake、Tiger
// 接下来会通过@Import的各种用法将这些bean注入到容器中
@Data
public class Cat {
    private String name;
}

// 步骤2) 在主配置类上加上我们自定义的@EnableAnimal注解,含义就是通过@EnableAnimal会给容器中导入上述的那些动物Bean
// @EnableAnimal就可以类比我们上面说的@EnableAutoConfiguration注解,两者功能类似
@SpringBootApplication
@EnableAnimal
public class SpringbootApplication {
    public static void main(String[] args) {
       SpringApplication.run(SpringbootApplication.class, args);
    }
}

// 步骤3) 
// @EnableAnimal如下所示,这是我们自定义的注解,这个注解的核心是是在上面声明了@Import注解
// @Import注解可以传入四种类型,普通类、配置类、ImportSelector的实现类、ImportBeanDefinitionRegistar的实现类
// 下面分别讲解@Import注解导入四种类型的用法
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Import({Dog.class, AnimalRegisterConfiguration.class, AnimalImportSelector.class, 
                                                       AnimalImportBeanDefinitionRegistar.class})
public @interface EnableAnimal {
}

// 1) 直接@Import({Dog.class}),则容器启动完成之后容器中就有Dog这个bean,注意Dog这个类我们并没有通过@Component方式注入

// 2) @Import ({AnimalRegisterConfiguration.class}),通过这种Import配置类形式也可以导入
 
@Configuration
public class AnimalRegisterConfiguration {
 
    @Bean
    public Cat cat(){
        return new Cat("cat");
    }
}

// 3) @Import({AnimalImportSelector.class}),通过返回一个Spring数组的方式,数组中可以方便的指定多个Bean
// 我们上面说的AutoConfigurationImportSelector就是这种方式,SpringBoot给容器中导入MybatisAutoConfiguration
// 等自动配置类就是通过这种方式导入的,第二节配置类解析会讲这个
public class AnimalImportSelector implements ImportSelector {
 
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[] {Tiger.class.getName()};
    }
}

// 4) @Import({AnimalImportBeanDefinitionRegistar.class}),通过手动编码方式向registry注入Bean
// 我们上面说的AutoConfigurationPackages.Registrar就是这种方式
 
public class AnimalImportBeanDefinitionRegistar implements ImportBeanDefinitionRegistrar {
 
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        registry.registerBeanDefinition("snake", new RootBeanDefinition(Snake.class));
    }
}

// 我们可以看到这个@ComponentScan注解上显示指定了两个Filter过滤条件,它是SpringBoot提供的一种扩展机制,能让我们
// 向IOC容器中注册一些自定义的组件过滤器,以便在包扫描的过程中过滤一些Bean
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
                      @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

// 这是TypeExcludeFilter的方法,可以看到它是获取容器中所有的TypeExcludeFilter,并遍历它们去过滤一些不想要的Bean
public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
    if (this.beanFactory instanceof ListableBeanFactory && getClass() == TypeExcludeFilter.class) {
  Collection<typeexcludefilter> delegates
                    = ((ListableBeanFactory) this.beanFactory).getBeansOfType(TypeExcludeFilter.class).values();
  for (TypeExcludeFilter delegate : delegates) {
      if (delegate.match(metadataReader, metadataReaderFactory)) {
    return true;
      }
  }
    }
    return false;
}

// 我们可以自定义一个TypeExcludeFilter,它的功能就是过滤掉User这个bean,不让它注入到容器中
@Component
public class MyTypeExcludeFilter extends TypeExcludeFilter {
 
    @Override
    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
        return User.class.getName().equals(metadataReader.getClassMetadata().getClassName());
    }
}
 
@Component
public class User {
    private String name;
}

// 可以看到AutoConfigurationExcludeFilter就是将自动配置类给过滤掉了，因为自动配置类xxxAutoConfiguration是通过
// 上面说的AutoConfigurationImportSelector方式导入的,没必要导入两次
public class AutoConfigurationExcludeFilter implements TypeFilter, BeanClassLoaderAware {
    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
        return isConfiguration(metadataReader) && isAutoConfiguration(metadataReader);
    }
}

// @ConditionalOnMissingBean是通过@Conditional注解和Condition接口的实现类(OnBeanCondition.class)来实现这个效果的
@Bean
@ConditionalOnMissingBean
public InternalResourceViewResolver defaultViewResolver() {

@Conditional(OnBeanCondition.class)
public @interface ConditionalOnMissingBean {

@FunctionalInterface
public interface Condition {
    boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
}

// 自定义一个Condition接口的实现类MyCondition,通过其matches方法来判断是否符合指定条件
public class MyCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        // 获取注解MyConditionAnotation注解上指定value对应的值,如果没有这个值,则不符合条件
        String[] value = (String[]) metadata.getAnnotationAttributes(MyConditionAnotation.class.getName()).get("value");
        for (String property : value){
            if(StringUtils.isEmpty(context.getEnvironment().getProperty(property))){
                return false;
            }
        }
        return true;
    }
}

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@Documented
@Conditional(MyCondition.class)
public @interface MyConditionAnotation {
    String[] value() default {};
}

// 通过@Component给容器中注入一个A类型Bean,条件是@MyConditionAnotation注解指定的key1、key2对应的值有配置
@Component
@MyConditionAnotation({"key1", "key2"})
public class A {
}

// 我们先来看下上面讲解@Import注解讲到的AutoConfigurationImportSelector,我们说通过它就可以导入SpringBoot提供那些
// 自动配置类. 下面是Import注解讲到的AutoConfigurationImportSelector的selectImport方法
@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
     // 忽略一些其他代码
     // 这里的含义就是通过SpringFactoriesLoader去加载META-INF/spring.factories中配置的那些xxxAutoConfiguration
     // 并放入String数组返回
     AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
                                                       annotationMetadata);
     return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
}
 
// 忽略中间过程调用,后面会分析，接下来就走到这里通过SpringFactoriesLoader去加载自动配置类
protected List<string> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
     // 具体调用看下面分析
     List<string> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
                                                                    getBeanClassLoader());
     return configurations;
}
 
protected Class<?> getSpringFactoriesLoaderFactoryClass() {
     return EnableAutoConfiguration.class;
}

public static List<string> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
    // org.springframework.boot.autoconfigure.EnableAutoConfiguration
    String factoryClassName = factoryClass.getName();
    // 获得一个Map,map形如<key,List<String>&gt;形式,后面getOrDefault是获取
    // org.springframework.boot.autoconfigure.EnableAutoConfiguration对应的实现类集合
    // 注意这里面不仅仅是加载自动配置类,也会加载监听器、初始化器那些容器配置的实现类,这里统一一次加载之后放到缓存中
    return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
 
// 带缓存功能,从各个jar包的META-INF/spring.factories文件中加载实现类,一个key可能包含多个实现
private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
    MultiValueMap<String, String> result = cache.get(classLoader);
    if (result != null) {
        // 缓存中有直接返回
        return result;
    }
 
    try {
        // FACTORIES_RESOURCE_LOCATION值是META-INF/spring.factories
        Enumeration<url> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
                                                       ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
        result = new LinkedMultiValueMap<>();
        while (urls.hasMoreElements()) {
            URL url = urls.nextElement();
            UrlResource resource = new UrlResource(url);
            Properties properties = PropertiesLoaderUtils.loadProperties(resource);
            for (Map.Entry<?, ?> entry : properties.entrySet()) {
                // 获取key
                String factoryClassName = ((String) entry.getKey()).trim();
                // 将value逗号分隔,获得各个具体的实现类
                for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
                    // 放入result中
                    result.add(factoryClassName, factoryName.trim());
                }
            }
        }
        cache.put(classLoader, result);
        // 返回的result见下图
        return result;
    }
}

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
 
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
 
        // 往容器中新增BeanDefinition
        GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
        beanDefinition.setBeanClass(Chicken.class);
        registry.registerBeanDefinition("beanFactoryPostProcessor-Chicken", beanDefinition);
 
        // 修改容器中原有的BeanDefinition
        BeanDefinition snake = registry.getBeanDefinition("snake");
        snake.setLazyInit(true);
    }
}

@Component
public class CatBeanPostProcessor implements BeanPostProcessor {
 
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
 
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof Cat){
            Cat cat = (Cat) bean;
            cat.setName("changeNameCat");
        }
        return bean;
    }
}

// 图中说的创建ConfigurableApplicationContext,默认创建的是普通的Servlet Web容器,就是下面这个
// 通过反射创建会走到其默认的构造函数
public AnnotationConfigServletWebServerApplicationContext() {
    // 这里面进去会走到下面代码
    this.reader = new AnnotatedBeanDefinitionReader(this);
    this.scanner = new ClassPathBeanDefinitionScanner(this);
}
 
// 走到这里
registerAnnotationConfigProcessors(registry, null);
 
// 走到这里
// 向容器中注入一个ConfigurationClassPostProcessor,它是BeanFactoryPostProcessor
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));
}
 
// 向容器中注入一个AutowiredAnnotationBeanPostProcessor,它是BeanPostProcessor,用于解决依赖注入的
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));
}

@Override  
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {  
    // 删掉一些非关键代码
    processConfigBeanDefinitions(registry);  
}

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {  
    List<beandefinitionholder> configCandidates = new ArrayList<>(); 
    // 获取容器中已注册的bean名字,见下图,注意,这里容器中这些BeanDefinition都是容器初始化过程中容器添加进去的
    // 不是我们业务代码的beanDefinition,这段代码其实是连贯的,为了注释图片方便才分开
    String[] candidateNames = registry.getBeanDefinitionNames();  
 
    for (String beanName : candidateNames) {  
  // 获取BeanDefinition
        BeanDefinition beanDef = registry.getBeanDefinition(beanName);  
  // 判断这个BeanDefinition的configurationClass属性是不是full或者lite,如果是认为已经处理过了,第一次时默认为空,
  // 走下面分支
        if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||  
            ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {  
            // 打印日志记录下
        } else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
      // 1) 下面先分析下这个checkConfigurationClassCandidate方法,这边看方法名也可以猜到是检测该类是不是配置类
      // 是配置类的意思就是它会给容器中引入bean,这个方法判断主要就是看这个类的元信息中有没有@Configuration注解
      // 有没有@Component注解、有没有@ComponentScan、@Import、@ImportResource注解,有没有@Bean方法
      // 构造一个BeanDefinitionHolder,放入configCandidates中
            configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));  
        }  
    }  
  
    // Return immediately if no @Configuration classes were found  
    // 上图中容易默认已经引入了7个BeanDefinition,经过上面检测发现默认就一个符合条件的配置类,即我们的主配置类
    // 这里面configCandidates就一个,就是SpringBootApplication
    if (configCandidates.isEmpty()) {  
        return;  
    }  
  
    // Sort by previously determined @Order value, if applicable 
    // 排序
    configCandidates.sort((bd1, bd2) -> {  
        int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());  
        int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());  
        return Integer.compare(i1, i2);  
    });  
  
    // 删掉部分代码
  
    // Parse each @Configuration class  
    // 配置类解析工具
    ConfigurationClassParser parser = new ConfigurationClassParser(  
                                this.metadataReaderFactory, this.problemReporter, this.environment,  
                                this.resourceLoader, this.componentScanBeanNameGenerator, registry);  
    // 待处理集合
    Set<beandefinitionholder> candidates = new LinkedHashSet<>(configCandidates);  
    // 已处理集合
    Set<configurationclass> alreadyParsed = new HashSet<>(configCandidates.size());  
    // 循环处理直到candidates.isEmpty()
    do {  
  // 这边开始解析,对应步骤4
        parser.parse(candidates);  
        parser.validate();  
        // 取出第四步解析得到的一些configurationClasses集合
        Set<configurationclass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());  
        configClasses.removeAll(alreadyParsed);  
  
        // 删除一部分代码
  // 这边也会去加载BeanDefinition,对应图中步骤五
        this.reader.loadBeanDefinitions(configClasses);  
        alreadyParsed.addAll(configClasses);  
   }  
   while (!candidates.isEmpty());  
}

ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory);
 
public static boolean checkConfigurationClassCandidate(BeanDefinition beanDef, 
                                                       MetadataReaderFactory metadataReaderFactory) {  
  
    String className = beanDef.getBeanClassName();  
    // 获取下类名,如果类名为空或者该类为工厂类
    if (className == null || beanDef.getFactoryMethodName() != null) {  
        return false;  
    }  
  
    // 获取类的元数据信息
    AnnotationMetadata metadata; 
    // 上图的7个candidateNames中只有一个springbootApplication是AnnotatedBeanDefinition,其余全返回false
    if (beanDef instanceof AnnotatedBeanDefinition &&
                  className.equals(((AnnotatedBeanDefinition) beanDef).getMetadata().getClassName())) {  
        // Can reuse the pre-parsed metadata from the given BeanDefinition... 
  // springbootApplication走到这里
        metadata = ((AnnotatedBeanDefinition) beanDef).getMetadata();  
    }  
    else if (beanDef instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) beanDef).hasBeanClass()) {  
        // Check already loaded Class if present...  
        // since we possibly can't even load the class file for this Class.  
  Class<?> beanClass = ((AbstractBeanDefinition) beanDef).getBeanClass();  
        metadata = new StandardAnnotationMetadata(beanClass, true);  
    }  
    else {  
        try {  
            MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(className);  
      // 读取类的元数据信息,这里面包括注解等信息
            metadata = metadataReader.getAnnotationMetadata();  
        }  
        catch (IOException ex) {  
            return false;  
        }  
    }  
  
    // metadata.isAnnotated(Configuration.class.getName()),这个就是判断类上面有没有@Configuration注解
    if (isFullConfigurationCandidate(metadata)) {  
  // 如果true的话设置下这个属性,那么就标记为处理过了
        beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);  
    } else if (isLiteConfigurationCandidate(metadata)) {  
        beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);  
    }  
    else {  
  // 其余6个返回false
        return false;  
    }  
  
    // It's a full or lite configuration candidate... Let's determine the order value, if any.  
    Integer order = getOrder(metadata);  
    if (order != null) { 
       // 获取下类上的@Order信息
       beanDef.setAttribute(ORDER_ATTRIBUTE, order);  
    }  
    return true;  
}

public static boolean isLiteConfigurationCandidate(AnnotationMetadata metadata) {  
    // Do not consider an interface or an annotation...  
    if (metadata.isInterface()) {  
        return false;  
    }  
  
    // Any of the typical annotations found?  
    for (String indicator : candidateIndicators) {  
  // 判断下类上面有没有这几个注解
        if (metadata.isAnnotated(indicator)) {  
           return true;  
        }  
    }  
  
    // Finally, let's look for @Bean methods...  
    try {  
        // 判断有没有@Bean的方法
        return metadata.hasAnnotatedMethods(Bean.class.getName());  
    }  
    return false;  
  }  
}
 
private static final Set<string> candidateIndicators = new HashSet<>();  
  
static {  
    candidateIndicators.add(Component.class.getName());  
    candidateIndicators.add(ComponentScan.class.getName());  
    candidateIndicators.add(Import.class.getName());  
    candidateIndicators.add(ImportResource.class.getName());  
}

public void parse(Set<beandefinitionholder> configCandidates) {  
    // 删除部分代码，实际执行时这里的configCandidates就一个springBootApplication代表的主配置类
    for (BeanDefinitionHolder holder : configCandidates) {
        // 获取BeanDefinition
        BeanDefinition bd = holder.getBeanDefinition();  
        // 我们的SpringBootApplication会走到这边,下面先分析这边
        parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName()); 
    }  
    // (**)处这边也要留意下,这边会处理DeferredImportSelector,我们前面说的AutoConfigurationImportSelector就是在这边处理
    // 给容器中导入xxxAutoConfiguration
    this.deferredImportSelectorHandler.process();  
}
 
protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {  
     processConfigurationClass(new ConfigurationClass(metadata, beanName));  
}
 
protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {  
     // 根据当前类上面的@Conditional注解标注的条件判断是否要解析这个配置类
     if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {  
        return;  
     }  
     // 以configClass作为key去获取,第一次来肯定是获取不到的,走下面逻辑
     ConfigurationClass existingClass = this.configurationClasses.get(configClass);  
     if (existingClass != null) {  
         if (configClass.isImported()) {  
             if (existingClass.isImported()) {  
                 existingClass.mergeImportedBy(configClass);  
             }  
             // Otherwise ignore new imported config class; existing non-imported class overrides it.  
             return;  
         }  
         else {  
             // Explicit bean definition found, probably replacing an import.  
             // Let's remove the old one and go with the new one.  this.configurationClasses.remove(configClass);  
             this.knownSuperclasses.values().removeIf(configClass::equals);  
          }  
      }  
  
      // Recursively process the configuration class and its superclass hierarchy.
      // 这一步其实没有做啥,重点还是看下一步骤
      SourceClass sourceClass = asSourceClass(configClass);  
      do {  
    // 这里是重点,里面具体分为8大步骤,单独拿一小节分析
    // b) doProcessConfigurationClass
          sourceClass = doProcessConfigurationClass(configClass, sourceClass);  
      }  
      while (sourceClass != null);  
     // 放入configurationClasses中
      this.configurationClasses.put(configClass, configClass);  
}

// 上面的asSourceClass最终其实就是封装了一个SourceClass对象
public SourceClass(Object source) {  
    this.source = source;  
    if (source instanceof Class) {  
        this.metadata = new StandardAnnotationMetadata((Class<?>) source, true);  
    }  
    else {  
        this.metadata = ((MetadataReader) source).getAnnotationMetadata();  
    }  
}

protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)  
      throws IOException {  
    // 判断这个类上面有没有@Component注解 
    if (configClass.getMetadata().isAnnotated(Component.class.getName())) {  
        // Recursively process any member (nested) classes first  
  // 如果有的话,遍历其内部类,然后也是调用doProcessConfigurationClass递归处理
        processMemberClasses(configClass, sourceClass);  
    }  
  
    // Process any @PropertySource annotations
    // 处理PropertySource注解,之前讲解属性配置也分析过,就是将该注解对应的属性文件加载到Environment中
    for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(  
                                               sourceClass.getMetadata(), PropertySources.class,  
                                               org.springframework.context.annotation.PropertySource.class)) {  
        if (this.environment instanceof ConfigurableEnvironment) {  
            processPropertySource(propertySource);  
        }  
    }  
  
    // Process any @ComponentScan annotations 
    // 处理@ComponentScan注解,将其指定的包下的bean注册到框架中
    Set<annotationattributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(  
                                         sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);  
    if (!componentScans.isEmpty() &&
             !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {  
        for (AnnotationAttributes componentScan : componentScans) {  
            // The config class is annotated with @ComponentScan -&gt; perform the scan immediately  
            Set<beandefinitionholder> scannedBeanDefinitions =  
                         this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());  
            // Check the set of scanned definitions for any further config classes and parse recursively if needed  
            for (BeanDefinitionHolder holder : scannedBeanDefinitions) {  
                 BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();  
                 if (bdCand == null) {  
                     bdCand = holder.getBeanDefinition();  
                 }  
                 if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {  
                     parse(bdCand.getBeanClassName(), holder.getBeanName());  
                 }  
            }  
        }  
    }  
  
    // Process any @Import annotations  
    // 处理Import注解
    processImports(configClass, sourceClass, getImports(sourceClass), true);  
  
    // Process any @ImportResource annotations  
    // 处理@ImportResource注解,可以通过它来指定xml文件,BeanFactory就会读取这个xml文件将bean注册进去
    AnnotationAttributes importResource =  
                           AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);  
    if (importResource != null) {  
        String[] resources = importResource.getStringArray("locations");  
        Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");  
        for (String resource : resources) {  
            String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);  
            configClass.addImportedResource(resolvedResource, readerClass);  
        }  
    }  
  
    // Process individual @Bean methods  
    // 处理我们的类中使用@Bean注解的方法,添加到configClass的beanMethod中
    Set<methodmetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);  
    for (MethodMetadata methodMetadata : beanMethods) {  
        configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));  
    }  
  
    // Process default methods on interfaces  
    // 处理接口的默认方法,遍历这个类的接口,判断有没有使用@Bean注解的非抽象方法,添加到configClass的beanMethod中
    processInterfaces(configClass, sourceClass);  
  
    // Process superclass, if any  
    // 递归处理父类,这边返回父类上层方法会递归处理
    if (sourceClass.getMetadata().hasSuperClass()) {  
       // 判断父类不为null且不在knownSuperclasses中且不以Java开头
       String superclass = sourceClass.getMetadata().getSuperClassName();  
       if (superclass != null && !superclass.startsWith("java") &&
                                              !this.knownSuperclasses.containsKey(superclass)) {  
           this.knownSuperclasses.put(superclass, configClass);  
           // Superclass found, return its annotation metadata and recurse  
           return sourceClass.getSuperClass();  
       }  
    }  
  
    // No superclass -&gt; processing is complete  
    return null;  
}

if (configClass.getMetadata().isAnnotated(Component.class.getName())) {  
    // Recursively process any member (nested) classes first  
    processMemberClasses(configClass, sourceClass);  
}
 
 
 // Register member (nested) classes that happen to be configuration classes themselves.
 private void processMemberClasses(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {  
     Collection<SourceClass> memberClasses = sourceClass.getMemberClasses(); 
     // 判断是否有内部类,没有的话直接不处理
     if (!memberClasses.isEmpty()) {  
         List<SourceClass> candidates = new ArrayList<>(memberClasses.size());  
         for (SourceClass memberClass : memberClasses) {  
       // 判断是否是配置类,判断也很简单,之前分析过,判断类上面有没有@Configuration注解、@Import、@ImportResource
       // @Component、@ComponentScan以及@Bean标注的方法
             if (ConfigurationClassUtils.isConfigurationCandidate(memberClass.getMetadata()) &&  
                     !memberClass.getMetadata().getClassName().equals(configClass.getMetadata().getClassName())) {  
      // 加入到candidates中然后排个序
                  candidates.add(memberClass);  
             }  
         }  
         OrderComparator.sort(candidates);  
         for (SourceClass candidate : candidates) {     
       // 防止A引入防止A引入B,B引入A
             if (this.importStack.contains(configClass)) {  
                this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));  
             }  
             else {  
                this.importStack.push(configClass);  
                try {  
        // 放入栈中并遍历处理这些配置类,也是递归处理,调用之前的doProcessConfigurationClass处理这个配置类
                    processConfigurationClass(candidate.asConfigClass(configClass));  
                }  
                finally {  
                    this.importStack.pop();  
                }  
             }  
         }  
    }  
}

@SpringBootApplication  
@PropertySource({"demo.properties"})  
public class Springboot2Application {

for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(  
                                                sourceClass.getMetadata(), PropertySources.class,  
                                                org.springframework.context.annotation.PropertySource.class)) {  
    if (this.environment instanceof ConfigurableEnvironment) {  
  // 这边就不进去看了,主要是读取@PropertySource注解指定的文件,将其封装成一个属性集放入到环境中
        processPropertySource(propertySource);  
    }  
}

Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(  
                                       sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);  
if (!componentScans.isEmpty() &&  
          !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {  
    for (AnnotationAttributes componentScan : componentScans) {  
        // The config class is annotated with @ComponentScan -> perform the scan immediately  
  // 下面先分析这个parse方法
        Set<BeanDefinitionHolder> scannedBeanDefinitions =  
                     this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());  
        // Check the set of scanned definitions for any further config classes and parse recursively if needed  
        for (BeanDefinitionHolder holder : scannedBeanDefinitions) {  
            BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();  
            if (bdCand == null) {  
                bdCand = holder.getBeanDefinition();  
            }  
      // 如果是配置类,再递归处理
            if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {  
                parse(bdCand.getBeanClassName(), holder.getBeanName());  
            }  
        }  
    }  
}

public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {  
    ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,  
                           componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);  
  
    Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");  
    boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass); 
    // 设置一个bean名字生成器,默认就是使用org.springframework.beans.factory.support.BeanNameGenerator
    scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :  
                                                                      BeanUtils.instantiateClass(generatorClass));  
  
    // 就是默认的
    ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");  
    if (scopedProxyMode != ScopedProxyMode.DEFAULT) {  
        scanner.setScopedProxyMode(scopedProxyMode);  
    }  
    else {  
        Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");  
  // 理解是元数据解析器
        scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));  
    }  
  
    // 设置下扫描的资源模式,是**/*.class
    scanner.setResourcePattern(componentScan.getString("resourcePattern"));  
  
    // 添加IncludeFilter和ExcludeFilter
    for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {  
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {  
            scanner.addIncludeFilter(typeFilter);  
        }  
    }  
    for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {  
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {  
            scanner.addExcludeFilter(typeFilter);  
        }  
    }  
    // 设置是否懒加载
    boolean lazyInit = componentScan.getBoolean("lazyInit");  
    if (lazyInit) {  
        scanner.getBeanDefinitionDefaults().setLazyInit(true);  
    }  
  
    // 解析扫描的包路径加入到basePackages中
    Set<String> basePackages = new LinkedHashSet<>();  
    String[] basePackagesArray = componentScan.getStringArray("basePackages");  
    for (String pkg : basePackagesArray) {  
        String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),  
                                                 ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);  
        Collections.addAll(basePackages, tokenized);  
    }  
    for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {  
  // 解析basePackageClasses所在的包并加入到basePackages
        basePackages.add(ClassUtils.getPackageName(clazz));  
    }  
     // 如果是空的,将声明该注解所在的类的包加入到basePackages
    if (basePackages.isEmpty()) {  
  // 通常我们的主配置类是没有声明包扫描的路径的,所以这里会将主配置类所在的包加到这里面
        basePackages.add(ClassUtils.getPackageName(declaringClass));  
    }  
  
    // 添加一个ExcludeFilter,跳过声明该注解的类
    scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {  
       @Override  
       protected boolean matchClassName(String className) {  
           return declaringClass.equals(className);  
       }  
    });  
    return scanner.doScan(StringUtils.toStringArray(basePackages));  
}

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {  
     Assert.notEmpty(basePackages, "At least one base package must be specified");  
     Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();  
     // 遍历所有的包路径
     for (String basePackage : basePackages) {  
   // 获取该包下面所有符合条件的BeanDefinition,然后遍历处理,下面会分析
         Set<BeanDefinition> candidates = findCandidateComponents(basePackage);  
         for (BeanDefinition candidate : candidates) {  
             ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);  
             candidate.setScope(scopeMetadata.getScopeName());  
       // 通过beanNameGenerator生成beanName
             String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
       // 这两个if判断逻辑比较简单,就是设置一些Lazy、DependsOn属性
             if (candidate instanceof AbstractBeanDefinition) {  
                postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);  
             }  
             if (candidate instanceof AnnotatedBeanDefinition) {  
                AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);  
             }  
       // 这边是检查下有没有之前定义过这个BeanDefinition
             if (checkCandidate(beanName, candidate)) {  
                BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);  
                definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, 
                                                      definitionHolder, this.registry);  
                // 将该beanDefinition加入到集合中,并注册到容器中
                beanDefinitions.add(definitionHolder);  
                registerBeanDefinition(definitionHolder, this.registry);  
             }  
        }  
    }  
    return beanDefinitions;  
}

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {  
     Set<BeanDefinition> candidates = new LinkedHashSet<>();  
     try {  
         // 扫描指定包路径及其子包下面的class文件,将其封装成Resource对象
   // classpath*:com/lwh/springboot/**/*.class
   String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +  
                                          resolveBasePackage(basePackage) + '/' + this.resourcePattern;  
         Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);  
   
         for (Resource resource : resources) {  
             if (resource.isReadable()) {  
                try {  
                    MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);  
                    if (isCandidateComponent(metadataReader)) {  
                         ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);  
                         sbd.setResource(resource);  
                         sbd.setSource(resource);  
                         if (isCandidateComponent(sbd)) {  
                             candidates.add(sbd);  
                         }  
                    }  
                }  
            }  
         }
    }
    return candidates;  
}

// 通过之前设置的几个filter进行过滤
protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {  
    for (TypeFilter tf : this.excludeFilters) {  
        if (tf.match(metadataReader, getMetadataReaderFactory())) {  
            return false;  
        }  
    }  
    for (TypeFilter tf : this.includeFilters) {  
        if (tf.match(metadataReader, getMetadataReaderFactory())) {  
            return isConditionMatch(metadataReader);  
        }  
    }  
    return false;  
}

// Process any @Import annotations  
// getImports方法就是去递归扫描configClass上面所有的注解,将@Import注解标注的值放入importCandidates中,见下图
processImports(configClass, sourceClass, getImports(sourceClass), true);

private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,  
                                     Collection<SourceClass> importCandidates, boolean checkForCircularImports) {  
  
    if (importCandidates.isEmpty()) {  
        return;  
    }  
  
    if (checkForCircularImports && isChainedImportOnStack(configClass)) {  
        this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));  
    }  
    else {  
        this.importStack.push(configClass);  
        try {  
            for (SourceClass candidate : importCandidates) {  
    // 依次遍历判断类型
    // 其中有一个是这个类型,@Import(AutoConfigurationImportSelector.class)
    // 这个就是自动配置原理,导入xxxAutoConfiguration这些类
                if (candidate.isAssignable(ImportSelector.class)) {  
                    // Candidate class is an ImportSelector -> delegate to it to determine imports  
                    Class<?> candidateClass = candidate.loadClass();  
        // 实例化并调用xxxAware的方法并注入相关属性
                    ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);  
                    ParserStrategyUtils.invokeAwareMethods(  
                                            selector, this.environment, this.resourceLoader, this.registry); 
        // 它是DeferredImportSelector类型的
                    if (selector instanceof DeferredImportSelector) {  
                  // deferredImportSelectors = new ArrayList<>()
      // 这边会将两个参数封装下加入到deferredImportSelectors中,后面处理
      // 加入到deferredImportSelectors中后,具体的处理是this.deferredImportSelectorHandler.process();
                        this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);  
                    }  
                    else {  
      // 不是的话获取@Import导入的类名数组
                        String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());  
                        Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames); 
      // 然后再递归处理
                        processImports(configClass, currentSourceClass, importSourceClasses, false);  
                    }  
                }  
    // @Import(AutoConfigurationPackages.Registrar.class),我们的主配置类上面的注解就是这个类型
    // 这个是用于导入主配置类所在包及其子包下的BeanDefinition
                else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {  
                     // Candidate class is an ImportBeanDefinitionRegistrar ->  
                     // delegate to it to register additional bean definitions  
                     Class<?> candidateClass = candidate.loadClass();  
                     ImportBeanDefinitionRegistrar registrar =  
                                BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);  
                     ParserStrategyUtils.invokeAwareMethods(  
                                               registrar, this.environment, this.resourceLoader, this.registry);  
         // 这边就是将这两个参数作为key,value放入了一个map中
               // this.importBeanDefinitionRegistrars.put(registrar, importingClassMetadata);
                     configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());  
                }  
                else {  
                     // Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->  
                     // process it as an @Configuration class  
               this.importStack.registerImport(  
                                     currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());  
         // 当做一个普通类处理,判断是不是配置类,递归处理
                     processConfigurationClass(candidate.asConfigClass(configClass));  
                }  
         }  
      }  
      finally {  
         this.importStack.pop();  
      }  
   }  
}

// 这种就是Spring中常用的通过XML形式注入的方式
@SpringBootApplication  
@ImportResource("test.xml")  
public class Springboot2Application {

// Process any @ImportResource annotations
// 可以使用@ImportResource注解指定xml文件,导入BeanDefinition
AnnotationAttributes importResource =  
                AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);  
if (importResource != null) {  
     String[] resources = importResource.getStringArray("locations");  
     Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");  
     for (String resource : resources) {  
   // 就是test.xml
         String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);  
         configClass.addImportedResource(resolvedResource, readerClass);  
     }  
}
 
public void addImportedResource(String importedResource, Class<? extends BeanDefinitionReader> readerClass) {  
     // 这边就是放入到了map中,这边是先统一存放起来,在步骤五的4)在真正进行导入BeanDefinition
     this.importedResources.put(importedResource, readerClass);  
}
 
private final Map<String, Class<? extends BeanDefinitionReader>> importedResources = new LinkedHashMap<>();

// Process individual @Bean methods  
// 获取当前类中的Bean方法
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);  
for (MethodMetadata methodMetadata : beanMethods) {  
     // 这边也是加入到set中,见下面代码,也是在步骤五的3)中进行处理
     configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));  
}
 
private final Set<BeanMethod> beanMethods = new LinkedHashSet<>();

// 默认方法举例,主配置类实现这个接口就可以
public interface ConfigurationInterface {
 
    @Bean
    default Pig pig(){
        return new Pig();
    }
}

// Process default methods on interfaces  
 processInterfaces(configClass, sourceClass);
 
 // Register default methods on interfaces implemented by the configuration class.
 // 这边也是递归处理其父接口,判断父接口中默认方法是不是@Bean方法
 private void processInterfaces(ConfigurationClass configClass, SourceClass sourceClass) throws IOException {  
     for (SourceClass ifc : sourceClass.getInterfaces()) {  
         Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(ifc);  
         for (MethodMetadata methodMetadata : beanMethods) {  
             if (!methodMetadata.isAbstract()) {  
                 // 也是在步骤五的3)中进行处理
                 configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));  
             }  
         }  
         processInterfaces(configClass, ifc);  
     }  
}