使用Spring BeanDefinition手动注册Bean

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {


  /**
   * Modify the application context's internal bean definition registry after its
   * standard initialization. All regular bean definitions will have been loaded,
   * but no beans will have been instantiated yet. This allows for adding further
   * bean definitions before the next post-processing phase kicks in.
   * @param registry the bean definition registry used by the application context
   * @throws org.springframework.beans.BeansException in case of errors
   */
  void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;


}

public class Person {


    private String name ;


    public void test(){
        System.out.println("hello world!");
    }


    public void setName(String name) {
        this.name = name;
    }
}

@EnableAspectJAutoProxy
@ComponentScan("com.jimbean.spring.test")
public class BootStrap {


    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext
               = new AnnotationConfigApplicationContext(BootStrap.class);
        DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) applicationContext.getBeanFactory();
        // 这里也可以使用 BeanDefinitionBuilder
        GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
        beanDefinition.setBeanClass(Person.class);
        beanFactory.registerBeanDefinition("person", beanDefinition);
        Person person = (Person) applicationContext.getBean("person");
        person.test();
    }
}

public class Person {


    private String name ;


    @Autowired
    Animal animal;


    public void test(){
        y.test();
        System.out.println("hello world!");
    }


    public void setName(String name) {
        this.name = name;
    }
}

@Component
public class Animal {


    public Animal() {
        System.out.println("Construct Animal");
    }


    public void test(){
        System.out.println("Animal.test()...");
    }


}

/**
   * Register a new bean definition with this registry.
   * Must support RootBeanDefinition and ChildBeanDefinition.
   * @param beanName the name of the bean instance to register
   * @param beanDefinition definition of the bean instance to register
   * @throws BeanDefinitionStoreException if the BeanDefinition is invalid
   * or if there is already a BeanDefinition for the specified bean name
   * (and we are not allowed to override it)
   * @see RootBeanDefinition
   * @see ChildBeanDefinition
   */
  void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
      throws BeanDefinitionStoreException;

@Override
  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 {
                //校验传入beanDefinition的正确性
        ((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) {
            //如果已存在该bean名称的beanDefinition，并且不允许覆盖，则抛异常
      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_INFRASTRUCTURE
        if (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 (!beanDefinition.equals(oldBeanDefinition)) {
        if (this.logger.isInfoEnabled()) {
          this.logger.info("Overriding bean definition for bean '" + beanName +
              "' with a different definition: replacing [" + oldBeanDefinition +
              "] with [" + beanDefinition + "]");
        }
      }
      else {
        if (this.logger.isDebugEnabled()) {
          this.logger.debug("Overriding bean definition for bean '" + beanName +
              "' with an equivalent definition: replacing [" + oldBeanDefinition +
              "] with [" + beanDefinition + "]");
        }
      }
      this.beanDefinitionMap.put(beanName, beanDefinition);
    }
    else {
            //检查beanFactory的bean创建阶段是否已开始,可以理解为容器是否已经初始化过了
      if (hasBeanCreationStarted()) {
        // Cannot modify startup-time collection elements anymore (for stable iteration)
        synchronized (this.beanDefinitionMap) {
                    //把新加入的beanName-beanDefinition映射加入beanDefinitionMap
                    //把beanName加入的维护的beanDefinitionName列表（ArrayList）中
          this.beanDefinitionMap.put(beanName, beanDefinition);
          List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
          updatedDefinitions.addAll(this.beanDefinitionNames);
          updatedDefinitions.add(beanName);
          this.beanDefinitionNames = updatedDefinitions;
                    //如果手动注册的单例bean名称包含了beanName，需要移除
                    //这个地方默认构造的beanDefinition对象作用域也是“”，等价于单例，但是却没有把 beanName加入到manualSingletonNames集合（LinkedHashSet）中
                    //最终beanName对应的bean实例化后，manualSingletonNames还是没有这个beanName，略奇怪。。。
          if (this.manualSingletonNames.contains(beanName)) {
            Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
            updatedSingletons.remove(beanName);
            this.manualSingletonNames = updatedSingletons;
          }
        }
      }
      else {
        // Still in startup registration phase
        this.beanDefinitionMap.put(beanName, beanDefinition);
        this.beanDefinitionNames.add(beanName);
        this.manualSingletonNames.remove(beanName);
      }
      this.frozenBeanDefinitionNames = null;
    }
        //如果oldBeanDefinition不为null，且单例池缓存中已经有beanName对应的bean，则重置给定bean的所有bean定义缓存，包括从其派生的bean的缓存。
    if (oldBeanDefinition != null || containsSingleton(beanName)) {
      resetBeanDefinition(beanName);
    }
  }

void registerSingleton(String beanName, Object singletonObject);

@EnableAspectJAutoProxy
@ComponentScan("com.jimbean.spring.test")
public class BootStrap {
 
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext
               = new AnnotationConfigApplicationContext(BootStrap.class);
        DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) applicationContext.getBeanFactory();
        beanFactory.registerSingleton("person", new Person());
        Person person = (Person) applicationContext.getBean("person");
        person.test();
    }
}