springboot~为接口添加动态代理

为接口添加动态代理，不需要添加接口实现，通过定义FactoryBean的方式实现，将自定义业务在InvocationHandler接口实现即可

ImportBeanDefinitionRegistrar

ImportBeanDefinitionRegistrar注入FactoryBean到SpringIOC中，而在FactoryBean中定义了类型T的动态代理，通过对InvocationHandler接口
的实现来添加自定义行为，这里使用jdk默认的代理，只支持接口类型。

使用场景

当需要为某个接口动态添加一种行为时，不需要建立它的实现类，可以通过动态代理去建立它的实现类，在代理中添加自定义的逻辑。

RunFactoryBean

public class RunFactoryBean<T> implements FactoryBean<T> {
  private Class<T> interfaceType;

  public Class<T> getInterfaceType() {
    return interfaceType;
  }

  public void setInterfaceType(Class<T> interfaceType) {
    this.interfaceType = interfaceType;
  }

  @Override
  public T getObject() throws Exception {
    InvocationHandler handler = (proxy, method, args) -> {
      System.out.println("代理T类型做一些事情");
      return null;
    };
    return (T) Proxy.newProxyInstance(interfaceType.getClassLoader(),
        new Class[]{interfaceType}, handler);
  }

  @Override
  public Class<?> getObjectType() {
    return interfaceType;
  }

RunFactoryBeanDefinitionRegistry

public class RunFactoryBeanDefinitionRegistry implements ImportBeanDefinitionRegistrar {
  @SneakyThrows
  @Override
  public void registerBeanDefinitions(AnnotationMetadata annotationMetadata,
                                      BeanDefinitionRegistry beanDefinitionRegistry) {
    Class beanClazz= Demo.Bird.class;
    BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(beanClazz);
    GenericBeanDefinition definition = (GenericBeanDefinition) builder.getRawBeanDefinition();

    MutablePropertyValues propertyValues = definition.getPropertyValues();
    propertyValues.add("interfaceType", beanClazz);
    definition.setBeanClass(RunFactoryBean.class);
    definition.setAutowireMode(GenericBeanDefinition.AUTOWIRE_BY_TYPE);
    beanDefinitionRegistry.registerBeanDefinition(beanClazz.getSimpleName(), definition);
  }
}

unit test

@Import({RunFactoryBeanDefinitionRegistry.class})
public class Demo {
  @Test
  public void run() {
    ApplicationContext applicationContext=new AnnotationConfigApplicationContext(Demo.class);
    Bird bird= applicationContext.getBean(Bird.class);
    bird.run();
  }

  interface Bird {
    void run();
  }
}

结果