Is there are any java annotation(s) that can validate like the example below?
String test;
test = null; //valid
test = ""; //invalid
test = " "; //invalid
test = "Some values"; //valid
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No, but you can write one of your own. :)Konstantin Yovkov– Konstantin Yovkov2015-06-30 07:48:24 +00:00Commented Jun 30, 2015 at 7:48
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This would be some kind of assurance. This is, what mutator methods are for. I do not think that there is an annotation for this (at least not in plain Java).Turing85– Turing852015-06-30 07:48:29 +00:00Commented Jun 30, 2015 at 7:48
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1any @Pattern(regexp = xxx) ???Yash Krishnan– Yash Krishnan2015-06-30 08:35:30 +00:00Commented Jun 30, 2015 at 8:35
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7 Answers
You need to create a custom annotation: @NullOrNotBlank
First create the custom annotation: NullOrNotBlank.java
@Target( {ElementType.FIELD})
@Retention(RUNTIME)
@Documented
@Constraint(validatedBy = NullOrNotBlankValidator.class)
public @interface NullOrNotBlank {
String message() default "{javax.validation.constraints.NullOrNotBlank.message}";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default {};
}
Then the actual validator: NullOrNotBlankValidator.java
public class NullOrNotBlankValidator implements ConstraintValidator<NullOrNotBlank, String> {
public void initialize(NullOrNotBlank parameters) {
// Nothing to do here
}
public boolean isValid(String value, ConstraintValidatorContext constraintValidatorContext) {
return value == null || value.trim().length() > 0;
}
}
6 Comments
Jefferson Lima
Just a quick one-liner for the validation:
return str == null || str.trim().length() > 0;
vegemite4me
@JeffersonLima I am not sure why my code is so verbose (I don't even like regex). Your one liner is spot on.
Peroxy
Great solution, I replaced the isValid check with:
return value == null || !value.isBlank(); since I am using Java 11.
Phil
FYI, this is possible to do without a custom annotation using javax.validation.constraints.Size. I've added an answer for this.
vegemite4me
@Phil unfortunately the Size annotation will count blank spaces, so cannot be used in this instance.
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There isn't such an annotation in either javax.validation or Hibernate Validator. There was a request to add one to Hibernate Validator but it was closed as "won't fix" due to the possibility of writing your own relatively easily. The suggest solution was to either use your own annotation type defined like this:
@ConstraintComposition(OR)
@Null
@NotBlank
@ReportAsSingleViolation
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
@Retention(RUNTIME)
@Constraint(validatedBy = { })
public @interface NullOrNotBlank {
String message() default "{org.hibernate.validator.constraints.NullOrNotBlank.message}";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default { };
}
or to use the @Pattern annotation with a regular expression that requires a non-whitespace character to be present (as the Pattern annotation accepts nulls and does not match them against the pattern).
1 Comment
Poke
+1 for the
@Pattern idea. This is great because many of the built-in annotations pass for null so that they don't conflict with @NotNullThis is possible without creating a custom annotation, by using javax.validation.constraints.Size
// Null values are considered valid
@Size(min=1) String test;
However as theprogrammer points out, blank strings such as " " are considered valid, which is not the case for @NotBlank.
4 Comments
solujic
such underrated solution +1
theprogrammer
But it will break blank strings of length 1 like "_"(where _ means space)
user07
This annotation is not applied for empty string, which is a string without any character
"" . It works if you have a string with few characters, "abc" , but it doesn't work if you have an empty string "".Phil
@user07 An annotation of
Size(min=1) triggers a violation constraint when the size of the string is 0, which is the case for an empty string.Where is a nice javax.validation.constraints.Pattern annotation.
You can annotate the field with:
@Pattern(regexp = "^(?!\\s*$).+", message = "must not be blank")
This checks if field matches regex. The regex itself is something but not blank (see details here). It uses negative lookahead.
answered Jul 15, 2020 at 18:21
Vladyslav Nikolaiev
2,0593 gold badges24 silver badges44 bronze badges
1 Comment
Radioactive
This regex is valid but I tried using it and SonarQube flagged it as a security hotspot.
The best way is to create your own constraint validator,
//custom annotation
@Documented
@Constraint(validatedBy = CustomCheck.class)
@Target( { ElementType.METHOD, ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
public @interface CustomConstarint {
String message() default "Invalid data";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
//validation logic goes here
public class CustomCheck implements
ConstraintValidator<CustomConstarint, String> {
@Override
public void initialize(CustomConstarint customConstarint) {
}
@Override
public boolean isValid(String field,
ConstraintValidatorContext cxt) {
//write your logic to validate the field
}
}
1 Comment
Arnav Karforma
For optional validations you could make use of jakarta.validation.constraints.AssertTrue, like
@AssertTrue(message = "if not null, your value must not be empty or blank")
private boolean isValueValid() {
if (value != null) {
return !value.trim().isEmpty();
}
return true;
}
Comments
Did you try Hibernate-Validator? I think that's what you are looking for.
import javax.validation.constraints.NotNull;
import org.hibernate.validator.constraints.NotBlank;
import org.hibernate.validator.constraints.NotEmpty;
public class MyModel {
@NotNull
private String str1;
@NotEmpty
private String str2;
@NotBlank
private String str3;
}
5 Comments
Yash Krishnan
No, I don't think so, I want all those validation over my single variable
bhdrk
@NotBlank validates for all of your requirements on a single variable. I just added the others if you want less validation. E.g. if your variable may contain blank char then use @NotEmpty or if it may contain empty string then use @NotNull.Yash Krishnan
bhdrk
I just try to explain the details of related to your questions. Not all. What's wrong?
Jules
None of these matches the requirements in the question, which are that the value should not be empty but may still be null. All of these validation constraints fail on null.