聊聊Spring的bean覆盖（存在同名name/id问题），介绍Spring名称生成策略接口BeanNameGenerator【享学Spring】（上）

public interface SingletonBeanRegistry {
  ...
  // ===注意它没有remove方法====
  void registerSingleton(String beanName, Object singletonObject);
  Object getSingleton(String beanName);
  boolean containsSingleton(String beanName);
  int getSingletonCount();
  ...
}

public interface BeanDefinitionRegistry extends AliasRegistry {
  ...
  void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException;
  // 请注意：SingletonBeanRegistry 可没有移除方法~
  void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
  BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
  boolean containsBeanDefinition(String beanName);
  int getBeanDefinitionCount();
  ...
}

// @since 2.0.3  是2.0后出来的
public interface BeanNameGenerator {
  // 入参竟然有两个  definition和bean定义注册器
  String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry);
}

// @since 2.0.3
public class DefaultBeanNameGenerator implements BeanNameGenerator {
  @Override
  public String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) {
    // isInnerBean 如果是内部类表示true，这个工具类也能处理
    return BeanDefinitionReaderUtils.generateBeanName(definition, registry);
  }
}

public abstract class BeanDefinitionReaderUtils {
  // unique, "#1", "#2" etc will be appended, until the name becomes 
  public static final String GENERATED_BEAN_NAME_SEPARATOR = BeanFactoryUtils.GENERATED_BEAN_NAME_SEPARATOR;
  // isInnerBean：是为了区分内部bean(innerBean）和顶级bean（top-level bean).
  public static String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry, boolean isInnerBean) throws BeanDefinitionStoreException {
    // 拿到Bean定义信息里面的BeanClassName全类名
    // 注意这个不是必须的，因为如果是继承关系，配上父类的依旧行了
    String generatedBeanName = definition.getBeanClassName();
    if (generatedBeanName == null) {
      // 若没有配置本类全类名，去拿到父类的全类名+$child"俩表示自己
      if (definition.getParentName() != null) {
        generatedBeanName = definition.getParentName() + "$child";
      }
      // 工厂Bean的  就用方法的名字+"$created"
      else if (definition.getFactoryBeanName() != null) {
        generatedBeanName = definition.getFactoryBeanName() + "$created";
      }
    }
    // 若一个都没找到，抛错~
    if (!StringUtils.hasText(generatedBeanName)) {
      throw new BeanDefinitionStoreException("Unnamed bean definition specifies neither " + "'class' nor 'parent' nor 'factory-bean' - can't generate bean name");
    }
    //isInnerBean=true表示你是内部类的话，名字又增加了如下变化
    String id = generatedBeanName;
    if (isInnerBean) {
      // Inner bean: generate identity hashcode suffix.
      id = generatedBeanName + GENERATED_BEAN_NAME_SEPARATOR + ObjectUtils.getIdentityHexString(definition);
    }
    // 如果不是内部类（绝大多数情况下都如此）
    // 此方法注意：一定能够保证到你的BeanName是唯一的~~~~
    else {
      // Top-level bean: use plain class name with unique suffix if necessary.
      // Top-level表示最外层的Bean，也就是说非内部类  这里生成绝对唯一的BeanName~~~~
      return uniqueBeanName(generatedBeanName, registry);
    }
    return id;
  }
  public static String uniqueBeanName(String beanName, BeanDefinitionRegistry registry) {
    String id = beanName;
    int counter = -1;
    // Increase counter until the id is unique.
    while (counter == -1 || registry.containsBeanDefinition(id)) {
      counter++;
      id = beanName + GENERATED_BEAN_NAME_SEPARATOR + counter;
    }
    return id;
  }
}

// @since 11.12.2003
public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader, EnvironmentCapable {
  private BeanNameGenerator beanNameGenerator = new DefaultBeanNameGenerator();
  public void setBeanNameGenerator(@Nullable BeanNameGenerator beanNameGenerator) {
    this.beanNameGenerator = (beanNameGenerator != null ? beanNameGenerator : new DefaultBeanNameGenerator());
  } 
}

//  @since 2.5 它的出现是伴随着@Component出现
public class AnnotationBeanNameGenerator implements BeanNameGenerator {
  // 支持的最基本的注解（包含其派生注解）
  private static final String COMPONENT_ANNOTATION_CLASSNAME = "org.springframework.stereotype.Component";
  @Override
  public String generateBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) {
    // //判断是否是否是AnnotatedBeanDefinition的子类， AnnotatedBeanDefinition是BeanDefinition的一个子类
    // 显然这个生成器只为AnnotatedBeanDefinition它来自动生成名称
    if (definition instanceof AnnotatedBeanDefinition) {
      // determineBeanNameFromAnnotation这个方法简而言之，就是看你的注解有没有标注value值，若指定了就以指定的为准
      // 支持的所有注解：上面已经说明了~~~
      // 此处若配置了多个注解且都指定了value值，但发现value值有不同的，就抛出异常了~~~~~
      String beanName = determineBeanNameFromAnnotation((AnnotatedBeanDefinition) definition);
      if (StringUtils.hasText(beanName)) {
        // Explicit bean name found.
        return beanName;
      }
    }
    // Fallback: generate a unique default bean name.
    // 若没指定，此处叫交给生成器来生成吧~~~
    return buildDefaultBeanName(definition, registry);
  }
  // 它的方法是protected 由此可见若我们想自定义生成器的话  可以继承它  然后复写
  protected String buildDefaultBeanName(BeanDefinition definition, BeanDefinitionRegistry registry) {
    return buildDefaultBeanName(definition);
  }
  // 这里是先拿到ClassUtils.getShortName 短名称
  protected String buildDefaultBeanName(BeanDefinition definition) {
    String beanClassName = definition.getBeanClassName();
    Assert.state(beanClassName != null, "No bean class name set");
    String shortClassName = ClassUtils.getShortName(beanClassName);
    // 调用java.beans.Introspector的方法  首字母小写
    return Introspector.decapitalize(shortClassName);
  }
}

public class AnnotatedBeanDefinitionReader {
  ...
  private BeanNameGenerator beanNameGenerator = new AnnotationBeanNameGenerator();
  ...
}