Null 但既不是 Empty 也不是 Blank 的 Java 注释

Question

是否有任何 java 注释可以像下面的示例一样进行验证？

String test;
test = null; //valid
test = ""; //invalid
test = " "; //invalid
test = "Some values"; //valid

Answer 1

您需要创建自定义注解:@NullOrNotBlank

首先创建自定义注解: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 {};
}

然后是实际的 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;
    }
}