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spring-bootannotations

Using annotations in spring boot for putting data in correct format

I have a field in my entity that holds phone-number. According to the conventions of the project, I need to save it in E.164 format in the DB. At the moment I use @PrePersist and @PreUpdate annotations for changing the phone number to the specified format. This method is good for one or two entities but it becomes very error-prone when you have to repeat it over and over.

I was thinking that it would be awesome if I could put the code in annotation and the annotation reads the fields and changes its value just before the persistence something like what @LastModifiedDate and annotation do. I searched the web for the codes of this annotation but I didn't understand how they managed it.

How I can write an annotation that reads the value of a field and changes it before persistence, and how I can do it before some specific operations like delete (I want to set some params before deleting the object too)

Solution

  • Take a look at EntityListeners.

    You can create a listener that checks your custom annotation and triggers the appropriate methods.

    @Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface TheCustomAnnotation{
}

    @Entity
@EntityListeners(TheListener.class)
public class TheEntity {

    @TheCustomAnnotation
    private String phoneNumber;


    
public class TheListener {

    @PrePersist
    public void prePersist(Object target) {
        for(Field field : target.getClass().getDeclaredFields()){
          Annotation[] annotations = field.getDeclaredAnnotations();
          // Iterate annotations and check if yours is in it.
        }
    }

    This is just an example.