开始学注解

手写一个验证邮箱字段的注解：
首先项目中需要引入包：javax.validation:validation-api-1.1.0.Final.jar

好，开始写一个注解

@Documented
@Constraint(validatedBy = EmailValidator.class)
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.ANNOTATION_TYPE, ElementType.PARAMETER, ElementType.CONSTRUCTOR})//注解作用对象
@Retention(RetentionPolicy.RUNTIME)//注解作用时间
public @interface Email {
    boolean allowEmpty() default true;

    String message() default "is not a email";

    Class[] groups() default {};

    Class[] payload() default {};
}

EmailValidator.java

public class EmailValidator implements ConstraintValidator {
    boolean allowEmpty = false;

    @Override
    public void initialize(Email email) {
        allowEmpty = email.allowEmpty();
    }

    @Override
    public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
        return (allowEmpty && StringUtils.isEmpty(s)) || (StringUtils.isNotEmpty(s) && s.matches ("^[a-z_0-9.-]{1,64}@([a-z0-9-]{1,200}.){1,5}[a-z]{1,6}$"));
    }
}

使用：在标识email的字段上添加注解@Email就能校验这个是否满足email的判断规则