在Springboot项目中，我们时常要对从前端传入的domain对象进行验证，检验它是否合法然后再进行后续的操作，这个时候我们就可以使用Springboot自带的验证功能来完成这一操作。

步骤

I. 创建domain类并附上@SomeConstraint注解：

import java.io.Serializable;
import javax.validation.constraints.NotBlank;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.extern.slf4j.Slf4j;

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Slf4j
@StudentSearchConstraint
public class Search implements Serializable {

    private String name;
    private String age;
    private String gender;

    @NotBlank
    private String uniNo;

}

II. 创建Constraint注解：

@Documented
@Constraint(validatedBy = StudentSearchValidator.class)
@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
public @interface StudentSearchConstraint {
    String message() default "Error 400 - Uni No. is missing or empty in student search request";

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

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

III. 创建Validator类，用于实现Constraint注解：

package com.schwarzit.dmm.core.validator;

import com.schwarzit.dmm.core.domain.Search;
import java.util.Objects;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import org.apache.commons.lang3.StringUtils;

public class StudentSearchValidator implements ConstraintValidator<SearchConstraint, Student> {

    @Override
    public boolean isValid(Student student, ConstraintValidatorContext context) {

        if (StringUtils.isBlank(student.getUniNo())) {
            return false;
        }

        return hasOneRequiredField(student);
    }

    private static boolean hasOneRequiredField(Student student) {
        return StringUtils.isNotBlank(search.getUniNo()) ||
            StringUtils.isNotBlank(search.getName()) ||
            StringUtils.isNotBlank(search.getAge()) ||
            StringUtils.isNotBlank(search.getGender());
    }
}

完成之后，当传入的domain对象不符合要求时程序就会抛出异常。