[Java] Check if the character string is composed only of blanks (= Blank)

I was curious about the contents of the validator of javax.validation.constraints.NotBlank, so I checked it.


A code that returns true if it is blank.

public boolean isBlank(CharSequence charSequence) {
    if ( charSequence == null ) {
        return true;

    return charSequence.toString().trim().length() == 0;

Reference source

This code is borrowed from the implementation of  Ľorg.hibernate.validator.internal.constraintvalidators.bv.NotBlankValidator`.

 * Hibernate Validator, declare and validate application constraints
 * License: Apache License, Version 2.0
 * See the license.txt file in the root directory or <http://www.apache.org/licenses/LICENSE-2.0>.
package org.hibernate.validator.internal.constraintvalidators.bv;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import javax.validation.constraints.NotBlank;

 * Check that a character sequence is not {@code null} nor empty after removing any leading or trailing whitespace.
 * @author Guillaume Smet
public class NotBlankValidator implements ConstraintValidator<NotBlank, CharSequence> {

	 * Checks that the character sequence is not {@code null} nor empty after removing any leading or trailing
	 * whitespace.
	 * @param charSequence the character sequence to validate
	 * @param constraintValidatorContext context in which the constraint is evaluated
	 * @return returns {@code true} if the string is not {@code null} and the length of the trimmed
	 * {@code charSequence} is strictly superior to 0, {@code false} otherwise
	public boolean isValid(CharSequence charSequence, ConstraintValidatorContext constraintValidatorContext) {
		if ( charSequence == null ) {
			return false;

		return charSequence.toString().trim().length() > 0;

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