Spring框架中ImportBeanDefinitionRegistrar的应用详解

public interface ImportBeanDefinitionRegistrar {
	//虽然是俩方法，但是等于一个方法
	default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry,
         BeanNameGenerator importBeanNameGenerator) {
	//直接调用了下面的方法
      registerBeanDefinitions(importingClassMetadata, registry);
   }
   default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
   }
}

registry.registerBeanDefinition(String beanName, BeanDefinition beanDefinition)

public interface ImportTestDao {
   public void query();
}

@Component
public class ImportTestService {
    @Autowired
    ImportTestDao importTestDao;
    public void find(){
        System.out.println("ImportTestService importTestDao.query()");
        importTestDao.query();
    }
}

@ComponentScan("com.demo")
public class AppConfig {
}

public class Test {
   public static void main(String[] args) {
     AnnotationConfigApplicationContext anno= new AnnotationConfigApplicationContext(AppConfig.class);
     ImportTestDao importTestDao= (ImportTestDao) anno.getBean("importTestDao");
     importTestDao.query();
   }
}

public class MyImportDBR implements ImportBeanDefinitionRegistrar {
   @Override
   public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
   }
}

public class MyImportDBR implements ImportBeanDefinitionRegistrar {
   @Override
   public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
      //得到BD，扫描接口
      BeanDefinitionBuilder builder= BeanDefinitionBuilder.genericBeanDefinition(ImportTestDao.class);
      GenericBeanDefinition beanDefinition= (GenericBeanDefinition) builder.getBeanDefinition();
      beanDefinition.getConstructorArgumentValues().addGenericArgumentValue(beanDefinition.getBeanClassName());
      registry.registerBeanDefinition("importTestDao",beanDefinition);
   }
}

public class MyfactoryBean implements FactoryBean {
   private Class clazz;
   public MyfactoryBean(Class clazz) {
      this.clazz=clazz;
   }
   @Override
   public Object getObject() throws Exception {
      Class[] clazzes=new Class[]{this.clazz};
      Object proxy= Proxy.newProxyInstance(this.getClass().getClassLoader(),clazzes,new MyInvocation());
      return proxy;
   }
   @Override
   public Class<?> getObjectType() {
      return this.clazz;
   }
   @Override
   public boolean isSingleton() {
      return false;
   }
}

public class MyInvocation implements InvocationHandler {
   public MyInvocation() {
   }
   @Override
   public Object invoke(Object proxy, Method method, Object[] args) {
   	  System.out.println("This is a proxy of ImportTestDao");
      return null;
   }
}

public class MyImportDBR implements ImportBeanDefinitionRegistrar {
   @Override
   public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
      //得到BD，扫描接口，这里笔者写死了，但是其实可以做一个包扫描，把某一个包下的所有类都扫描进来，就像Mybatis的@MapperScan注解一样
      BeanDefinitionBuilder builder= BeanDefinitionBuilder.genericBeanDefinition(ImportTestDao.class);
      //拿到一个BeanDefinition, 这里使用一个其中一个子类来接收，代表这里构建的就是一个普通的BeanDefinition
      GenericBeanDefinition beanDefinition= (GenericBeanDefinition) builder.getBeanDefinition();
      //这里打印是因为笔者当时不确定类名要不要包含包名
      System.out.println(beanDefinition.getBeanClassName());
      //给我们的beanDefinition添加一个构造方法，并且传入我们需要的bean名字
      beanDefinition.getConstructorArgumentValues().addGenericArgumentValue(beanDefinition.getBeanClassName());
      //把代理对象给赋予给BeanDefinition
      beanDefinition.setBeanClass(MyfactoryBean.class);
      //这里的名字可以随便取，这里是随着Spring名规范取的。话说这个接口的另一个方法有BeanNameGenerator这个参数就是让大家自由发挥的
      registry.registerBeanDefinition("importTestDao",beanDefinition);
   }
}

@Retention(RetentionPolicy.RUNTIME)
@Import(MyImportDBR.class)
public @interface MyScaner {
}

@ComponentScan("com.demo")
@MyScaner
public class AppConfig {
}
运行，拿到结果：
This is a proxy of ImportTestDao
query

<bean id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
  <property name="mapperInterface" value="org.mybatis.spring.sample.mapper.UserMapper" />
  <property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {
//通过这个接口反射代理对象，就是我们例子中的clazz
   private Class<T> mapperInterface;  
   public MapperFactoryBean() {
      // intentionally empty
   }
   public MapperFactoryBean(Class<T> mapperInterface) {
      this.mapperInterface = mapperInterface;
   }
   ...无关，略...
   /**
    * {@inheritDoc}
    */
   @Override
   public T getObject() throws Exception {
	//通过传入接口反射得到代理对象，如果没有接口你就没有办法获取代理对象
	//这个接口怎么拿到，就是通过上面的xml配置的
      return getSqlSession().getMapper(this.mapperInterface);
   }
   /**
    * {@inheritDoc}
    */
   @Override
   public Class<T> getObjectType() {
      return this.mapperInterface;
   }
   /**
    * {@inheritDoc}
    */
   @Override
   public boolean isSingleton() {
      return true;
   }
 // ...无关，略...
}