The difference between @notnull, @notblank, @notempty of commonly used verification annotations

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Entity field verification @NotNull、@NotEmpty、@NotBlank

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Not for null, But it can be empty, Generally used in Integer On the non empty check of the basic data type of type , And the fields marked by it can use @size、@Max、@Min Control the size of field values

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Not for null, And the length must be greater than 0, Generally used on collection classes or arrays

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It can only act on the received String On type , Note that Can only , Not for null, And call trim() after , The length must be greater than 0 namely ： There must be actual characters

• Pay attention to use @NotBlank When waiting for comments , Be sure to and @valid Use it together , otherwise @NotBlank It doesn't work .
• One BigDecimal The field verification label used by the field should be @NotNull.
• In the use of @Length Generally used in String In terms of type, the maximum length limit of field value can be controlled .
• In the use of @Range Generally used in Integer In terms of type, you can control the size range of field values .

As shown in the figure below ：

The following example ：

1.String name = null;

@NotNull: false
@NotEmpty:false 
@NotBlank:false 



2.String name = "";

@NotNull:true
@NotEmpty: false
@NotBlank: false



3.String name = " ";

@NotNull: true
@NotEmpty: true
@NotBlank: false



4.String name = "Hello World！";

@NotNull: true
@NotEmpty:true
@NotBlank:true

Common verification notes

javax.validation.constraints.xxx

annotation	explain
@Null	The limit can only be null
@NotNull	The limit must not be null
@AssertTrue	The limit must be true
@AssertFalse	The limit must be false
@Min(value)	The limit must be a number not less than the specified value
@Max(value)	The limit must be a number no greater than the specified value
@DecimalMin(value)	The restricted element must be a number , Its value must be greater than or equal to the specified minimum value
@DecimalMax(value)	The restricted element must be a number , Its value must be less than or equal to the specified maximum value
@Size(max,min)	The limit character length must be in min To max Within the specified range
@Digits(integer,fraction)	The limit must be a decimal , And the number of digits in the integer part cannot exceed integer、 The number of decimal places cannot exceed fraction Within the acceptable range
@Past	Restricted elements ( The date type ) It must be a date in the past
@Future	Restricted elements ( The date type ) It must be a future date
@Pattern(value)	The restriction must conform to the specified regular expression
@Email	The restricted element value is email address , You can also use regular expressions and flag Specify custom email
@Length	The size of the restricted string must be within the specified range
@NotEmpty	The restricted string must be non empty ( Not for null It's not empty )
@Range	The restricted elements must be within the appropriate range

• attach @JsonFormat

Sometimes use @JsonFormat When the annotation , The search time may be eight hours less than that in the database , This is caused by the time zone difference ,JsonFormat The default time zone is Greenwich Time, The default is Greenwich mean time , And we're in the East eighth District , So the time will be eight hours less than we actually want . You need to add a time zone after it , The following example ：

@JsonFormat(pattern="yyyy-MM-dd",timezone="GMT+8")
private Date date;

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