NullableLength.java

package validator;

import javax.validation.Constraint;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import javax.validation.Payload;
import java.lang.annotation.Documented;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static validator.NullableLength.*;
import static validator.NullableLength.StringValidator;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * 可以为null，如果不为null必须满足(min <= len <= max)条件
 */
@Constraint(validatedBy = {StringValidator.class})
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
@Retention(RUNTIME)
@Repeatable(List.class)
public @interface NullableLength {

    /**
     * 默认不对下限做校验
     * 检查空请用
     * {@link javax.validation.constraints.NotBlank}
     * {@link javax.validation.constraints.NotEmpty}
     * 相关注解
     */
    int min() default -1;

    int max() default Integer.MAX_VALUE;

    /**
     * 是否trim后进行判断
     * 如果trim=true，请确认是否和
     * {@link javax.validation.constraints.NotBlank}
     * {@link javax.validation.constraints.NotEmpty}
     * 等注解重复
     */
    boolean trim() default false;

    String message() default "{validator.NullableLength.message}";

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

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

    class StringValidator implements ConstraintValidator<NullableLength, String> {

        private NullableLength annotation;

        @Override
        public void initialize(NullableLength annotation) {
            this.annotation = annotation;
        }

        @Override
        public boolean isValid(String value, ConstraintValidatorContext context) {
            if (value == null) {
                return true;
            }
            int len = annotation.trim()
                    ? value.trim().length()
                    : value.length();
            return len >= annotation.min() && len <= annotation.max();
        }

    }

    @Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE })
    @Retention(RUNTIME)
    @Documented
    @interface List {
        NullableLength[] value();
    }

}