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1. Background

In her recent study, Lele found that others had their own definition of annotations, which she thought was very cool. Annotation is a kind of aspect, and it must be cool to realize it by herself, so Lele also wrote a custom annotation for email verification

The second practice

  1. Write an email verification note first

     @Target(ElementType.FIELD)
 @Retention(RetentionPolicy.RUNTIME)
 public @interface EmailValidate {
     String message();
 }
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  1. Write an annotation manager

    public class EmailValidateHandle { public static <T> String validator(T t) throws IllegalArgumentException, IllegalAccessException{ StringBuilder errorMessage = new StringBuilder(); Class<? extends Object> cla = t.getClass(); Field[] fields = cla.getDeclaredFields(); Field[] fields = cla.getDeclaredFields(); EmailValidate emailValidateAnnotation = f.getAnnotation(emailvalidate.class); for(Field f:fields){ if(null ! = emailValidateAnnotation){// Set some properties to be accessible. F.setaccessible (true); Object val = f.et (t); boolean flag = checkEmail(val); if(! Flag) {/ / comment on the abnormal information errorMessage. Append (emailValidateAnnotation. Message ()), append (", "); } } } return errorMessage.toString(); }}Copy the code

  2. Place the annotation on the property to validate

    /** * Recipient */ @emailValidate (message = "recipient email format is incorrect ") private String recipients; /** * @emailValidate (message = "ccEmail ") public String ccEmail;Copy the code

  3. Call it where it is needed

     String validator = EmailValidateHandle.validator(object);
 
 
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5. Custom annotations complete!