@ GeneratedValue
it is usually convenient to allow persistence implementations to automatically assign unique values to identity fields. JPA contains GeneratedValue annotations for this purpose. It has the following properties:

GenerationType policy: enumerates values that specify how field values are automatically generated. The GenerationType enumeration has the following values:

GeneratorType.AUTO: default value. Assigning the generated value to the field is up to the JPA vendor to decide the implementation (such as hibernate).

the GenerationType.IDENTITY: database will assign an identity value, such as MySQL's auto_increment, at insert time.

GenerationType.SEQUENCE: uses database sequences to generate field values, such as oracle.

GenerationType.TABLE: uses sequence tables to generate field values. As in the following example

@Entity
@Table(name = "JPAGEN_PERSON")
public class Person implements Serializable {
     
    @Id
    @GeneratedValue(strategy = GenerationType.TABLE,
            generator = "personGen")
    @TableGenerator(name = "personGen",
            table = "JPAGEN_GENERATORS",
            pkColumnName = "NAME",
            pkColumnValue = "JPAGEN_PERSON_GEN",
            valueColumnName = "VALUE")
    private long id;
 
    // other fields and methods are omitted 
}

as to which method you say is related to the implementation of jpa, you can take a look at this link

https://docs.spring.io/spring.

but since the underlying implementation is still hibernate, you can refer to the implementation of hibernate

ide/html_single/Hibernate_User_Guide.html-sharpannotations-hibernate-generatortype" rel=" nofollow noreferrer "> http://docs.jboss.org/hiberna.