@NotNull:The annotated element must not be {@code null}.Accepts any type.
只是校驗不能爲null,任何類型的數據都可以用
@NotEmpty:Asserts that the annotated string, collection, map or array is not {@code null} or empty.
校驗String、集合等不爲null不是空的(“ ”空格被認爲非空)
@NotBlank:Validate that the annotated string is not {@code null} or empty.The difference to {@code NotEmpty} is that trailing whitespaces are getting ignored.
校驗String不能爲null也不能爲“ ”。也就是說,如果是“ ”,@NotEmpty爲true,@NotBlank爲false。
三者關係:@NotNull爲其他兩個的元註解。如下圖