Spring中@NotNull、@NotBlank、@NotEmpty的区别

@NotNull:// 可以用在所有类型上面，带有@NotNull注解的元素不能为null。对于集合类型的，没有size的约束。

@NotEmpty:// String, Collection, Map 和 Array 对象不能是 null 并且相关对象的 size 大于 0。

@NotBlank:// String去除了前后两段的空白字符串之后是否为null或者空的。

@NotNull：

看源码可知，@NotNull可以用在所有类型上面，带有@NotNull注解的元素不能为null。

/**
 * The annotated element must not be {@code null}.
 * Accepts any type.
 *
 * @author Emmanuel Bernard
 */
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
@Retention(RUNTIME)
@Documented
@Constraint(validatedBy = { })
public @interface NotNull {

	String message() default "{javax.validation.constraints.NotNull.message}";

	Class<?>[] groups() default { };

	Class<? extends Payload>[] payload() default { };

	/**
	 * Defines several {@link NotNull} annotations on the same element.
	 *
	 * @see javax.validation.constraints.NotNull
	 */
	@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
	@Retention(RUNTIME)
	@Documented
	@interface List {

		NotNull[] value();
	}
}

@NotEmpty:

看源码可知，带有@NotEmpty注解的String, Collection, Map或者Array不能为null或者为空。

@Size(min = 1)这个注解同时约束了集合的size的最小值为1，就是说空集合也会被判空。

/**
 * Asserts that the annotated string, collection, map or array is not {@code null} or empty.
 *
 * @author Emmanuel Bernard
 * @author Hardy Ferentschik
 */
@Documented
@Constraint(validatedBy = { })
@SupportedValidationTarget(ValidationTarget.ANNOTATED_ELEMENT)
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
@Retention(RUNTIME)
@ReportAsSingleViolation
@NotNull
@Size(min = 1)
public @interface NotEmpty {
	String message() default "{org.hibernate.validator.constraints.NotEmpty.message}";

	Class<?>[] groups() default { };

	Class<? extends Payload>[] payload() default { };

	/**
	 * Defines several {@code @NotEmpty} annotations on the same element.
	 */
	@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
	@Retention(RUNTIME)
	@Documented
	public @interface List {
		NotEmpty[] value();
	}
}

@NotBlank：

看源码注释可知，@NotBlank是用于判断String去除了前后两段的空白字符串之后是否为null或者空的。

/**
 * Validate that the annotated string is not {@code null} or empty.
 * The difference to {@code NotEmpty} is that trailing whitespaces are getting ignored.
 *
 * @author Hardy Ferentschik
 */
@Documented
@Constraint(validatedBy = { })
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
@Retention(RUNTIME)
@ReportAsSingleViolation
@NotNull
public @interface NotBlank {
	String message() default "{org.hibernate.validator.constraints.NotBlank.message}";

	Class<?>[] groups() default { };

	Class<? extends Payload>[] payload() default { };

	/**
	 * Defines several {@code @NotBlank} annotations on the same element.
	 */
	@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
	@Retention(RUNTIME)
	@Documented
	public @interface List {
		NotBlank[] value();
	}
}