Spring Framework之扫描注册机制（五）

一、前言

声明：Spring Framework将以本篇带来末结

通过前面五篇，我们对Bean加载、Bean依赖都有了深刻的认识，关于扫描Spring Framework是怎么做的了？通过下面2点我们将了解简单的Spring：
1.扫描注册机制的应用
2.游走ClassPathBeanDefinitionScanner扫描机制源码

二、扫描注册机制的应用

下面将会给未接触过的人也能一眼看懂，给接触过的人一个简短的温故

准备
类结构图

类结构

package mybean;

import org.springframework.stereotype.Component;

@Component
public class Bean1 {

}
-------------------------------------------------------------
package mybean;

import org.springframework.stereotype.Component;

@Component
public class Bean2 {

}
-------------------------------------------------------------
package mybean;

import org.springframework.context.annotation.ComponentScan;

@ComponentScan
public class ScanBean {

}

手动上下文扫描

• junit代码块

  @Test
  public void Test(){
    // 构建应用上下文
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
    context.scan("mybean");
    // 刷新应用上下文
    context.refresh();
    Arrays.asList(context.getBeanDefinitionNames())
      .forEach(System.out::println);
  }

• 执行输出结果

  缺少scanBean原因：Spring Framework是过滤掉了一些Bean，原生的默认支持@Component扫描自动注册

  org.springframework.context.annotation.internalConfigurationAnnotationProcessor
  org.springframework.context.annotation.internalAutowiredAnnotationProcessor
  org.springframework.context.event.internalEventListenerProcessor
  org.springframework.context.event.internalEventListenerFactory
  bean1
  bean2

自动Bean配置扫描

• junit代码块

  @Test
  public void Test(){
    // 构建应用上下文
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
    context.register(ScanBean.class);
    // 刷新应用上下文
    context.refresh();
    Arrays.asList(context.getBeanDefinitionNames())
      .forEach(System.out::println);
  }

• 执行输出结果

  org.springframework.context.annotation.internalConfigurationAnnotationProcessor
  org.springframework.context.annotation.internalAutowiredAnnotationProcessor
  org.springframework.context.event.internalEventListenerProcessor
  org.springframework.context.event.internalEventListenerFactory
  scanBean
  bean1
  bean2

三、游走ClassPathBeanDefinitionScanner扫描机制源码

由于扫描注册有两套机制，下文呼应所有Spring Framework文章，全面对自动Bean配置扫描进行解析，其中手动上下文扫描也会走到其中，下面会重点说明；主要类为ConfigurationClassPostProcessor，执行时机为上下文刷新中invokeBeanFactoryPostProcessors(beanFactory);

ConfigurationClassPostProcessor结构图

ConfigurationClassPostProcessor

这是Spring的内置Bena配置对象，前文学了BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry();回调流程，这边直接跟进

由于processConfigBeanDefinitions代码过多，直接贴出源码（删除了一些不明确的源码）

//处理配置bean定义
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
  List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
  String[] candidateNames = registry.getBeanDefinitionNames();

  //筛选配置Bean
  for (String beanName : candidateNames) {
    BeanDefinition beanDef = registry.getBeanDefinition(beanName);
    if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) {
      //...
    }
    //检查配置bean
    else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
      //装载ScanBean
      configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
    }
  }

  //没有配置需要处理 -> 跳出
  if (configCandidates.isEmpty()) {
    return;
  }

  //优先级排序
  configCandidates.sort((bd1, bd2) -> {
    int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
    int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
    return Integer.compare(i1, i2);
  });

  //为registry绑定BeanName生成器
  SingletonBeanRegistry sbr = null;
  if (registry instanceof SingletonBeanRegistry) {
    sbr = (SingletonBeanRegistry) registry;
    if (!this.localBeanNameGeneratorSet) {
      BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(
        AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR);
      if (generator != null) {
        this.componentScanBeanNameGenerator = generator;
        this.importBeanNameGenerator = generator;
      }
    }
  }

  //共享环境绑定
  if (this.environment == null) {
    this.environment = new StandardEnvironment();
  }

  //配置类解析器 -> 解析配置
  ConfigurationClassParser parser = new ConfigurationClassParser(
    this.metadataReaderFactory, this.problemReporter, this.environment,
    this.resourceLoader, this.componentScanBeanNameGenerator, registry);

  Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
  Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
  do {
    StartupStep processConfig = this.applicationStartup.start("spring.context.config-classes.parse");
    parser.parse(candidates);//解析ScanBean⬅️
    parser.validate();//验证

    Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
    configClasses.removeAll(alreadyParsed);

    if (this.reader == null) {
      this.reader = new ConfigurationClassBeanDefinitionReader(
        registry, this.sourceExtractor, this.resourceLoader, this.environment,
        this.importBeanNameGenerator, parser.getImportRegistry());
    }
    //注册配置解析出来的Bean定义
    this.reader.loadBeanDefinitions(configClasses);
    //...
  }
  while (!candidates.isEmpty());

  if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
    //注册导入单例
    sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
  }
  //...
}

ConfigurationClassParser




ComponentScanAnnotationParser

ClassPathBeanDefinitionScanner

其中注册的逻辑就不进行说明了，可以看前面更系统的了解

ClassPathScanningCandidateComponentProvider

当前为单个包的扫描机制，与手动上下文扫描对应