java - Spring自定义注解：如何继承属性？

Question

我正在创建自己的自定义快捷方式注释，如Spring 文档中所述：

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Transactional(value = "Custom", readOnly = true)
public @interface CustomTransactional {
}

是否有可能，通过我的自定义注释，我还可以设置任何其他属性，这些属性在@Transactional? 我希望能够使用我的注释，例如，像这样：

@CustomTransactional(propagation = Propagation.REQUIRED)
public class MyClass {

}

Answer 1

不，如果您想要以这种方式在自定义注释本身上设置的其他属性，那将不起作用：

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Transactional(value = "Custom", readOnly = true, propagation = Propagation.REQUIRED)
public @interface CustomTransactional {
}

一个解决方案（不好的一个:-)）可能是使用您在场景中看到的基本案例集定义多个注释：

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Transactional(value = "Custom", readOnly = true, propagation = Propagation.REQUIRED)
public @interface CustomTransactionalWithRequired {
}

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Transactional(value = "Custom", readOnly = true, propagation = Propagation.SUPPORTED)
public @interface CustomTransactionalWithSupported {
}

Answer 2

In (at least) Spring 4, you can do this by specifying the element inside the annotation, e.g.:

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Transactional(value = "Custom", readOnly = true)
public @interface CustomTransactional {
    Propagation propagation() default Propagation.SUPPORTED;
}

Source: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/beans.html#beans-meta-annotations