校驗類注解的區別 @NotNull、@NotEmpty、@NotBlank

使用場景

• @NotEmpty用在集合類
• @NotBlank 用在String
• @NotNull 用在基本類型

注解的探究

@NotEmpty

/**
 * The annotated element must not be {@code null} nor empty.
 * <p>
 * Supported types are:
 * <ul>
 * <li>{@code CharSequence} (length of character sequence is evaluated)</li>
 * <li>{@code Collection} (collection size is evaluated)</li>
 * <li>{@code Map} (map size is evaluated)</li>
 * <li>Array (array length is evaluated)</li>
 * </ul>
 *
 * @author Emmanuel Bernard
 * @author Hardy Ferentschik
 *
 * @since 2.0
 */
@Documented
@Constraint(validatedBy = { })
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
@Retention(RUNTIME)
@Repeatable(List.class)
public @interface NotEmpty {

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

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

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

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

@NotEmpty的String類、Collection、Map、數組，是不能為null並且長度必須大於0的（String、Collection、Map的isEmpty()方法）。

@NotBlank

/**
 * The annotated element must not be {@code null} and must contain at least one
 * non-whitespace character. Accepts {@code CharSequence}.
 *
 * @author Hardy Ferentschik
 * @since 2.0
 *
 * @see Character#isWhitespace(char)
 */
@Documented
@Constraint(validatedBy = { })
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
@Retention(RUNTIME)
@Repeatable(List.class)
public @interface NotBlank {

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

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

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

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

@NotBlank用於String，只能作用在String上，不能為null，而且調用trim()后，長度必須大於0。

@NotNull

/**
 * The annotated element must not be {@code null}.
 * Accepts any type.
 *
 * @author Emmanuel Bernard
 */
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
@Retention(RUNTIME)
@Repeatable(List.class)
@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, TYPE_USE })
	@Retention(RUNTIME)
	@Documented
	@interface List {

		NotNull[] value();
	}
}

接受任何類型，要求非空

常用注解示例

String

@NotBlank(message = "姓名不能為空！")
@Length(min = 2, max = 10, message = "姓名的長度只能在{min}到{max}之間！")
@Pattern(regexp = "^(((13[0-9])|(14[579])|(15([0-3]|[5-9]))|(16[6])|(17[0135678])|(18[0-9])|(19[89]))\\d{8})$", message = "手機號格式不正確")

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