java 检查注释是否属于特定类型
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Checking if an annotation is of a specific type
提问by Vivin Paliath
I am using reflection to see if an annotation that is attached to a property of a class, is of a specific type. Current I am doing:
我正在使用反射来查看附加到类属性的注释是否属于特定类型。目前我正在做：
if("javax.validation.Valid".equals(annotation.annotationType().getName())) {
...
}
Which strikes me as a little kludgey because it relies on a string that is a fully-qualified class-name. If the namespace changes in the future, this could cause subtle errors.
这让我觉得有点笨拙，因为它依赖于一个完全限定类名的字符串。如果命名空间在未来发生变化，这可能会导致细微的错误。
I would like to do:
我想要做：
if(Class.forName(annotation.annotationType().getName()).isInstance(
new javax.validation.Valid()
)) {
...
}
But javax.validation.Validis an abstract class and cannot be instantiated. Is there a way to simulate instanceof(or basically use isInstance) against an interface or an abstract class?
但是javax.validation.Valid是抽象类，不能实例化。有没有办法针对接口或抽象类模拟instanceof（或基本上使用isInstance）？
回答by Affe
Are you just looking for
你只是在寻找
if (annotation.annotationType().equals(javax.validation.Valid.class)){}
?
?
回答by yurez
Or even simpler:
或者更简单：
if (annotation instanceof Valid) { /* ... */ }
回答by sleske
Just for completeness' sake, another possibility is
为了完整起见，另一种可能性是
if (this.getClass().isAnnotationPresent(MyCustomAnnotation.class)) {
回答by Vivin Paliath
Ok, I guess I should have done a little more research before posting the question. I discovered that I could use Class.isAssignableFrom(Class<?> cls):
好的，我想我应该在发布问题之前做更多的研究。我发现我可以使用Class.isAssignableFrom(Class<?> cls)：
import javax.validation.Valid;
if(Valid.class.isAssignableFrom(annotation.annotationType())) {
...
}
This seems to do the job. I'm not sure if there are any caveats to using this approach, though.
这似乎可以完成工作。不过，我不确定使用这种方法是否有任何注意事项。
回答by Jorn
Since an annotation is just a class, you can simply use an == compare:
由于注释只是一个类，您可以简单地使用 == 比较：
if (annotation.annotationType() == Valid.class) { /* ... */ }
