項目問SpringDataJpa項目，在運行的過程中出現的以下錯誤：
Caused by: org.hibernate.AnnotationException: An entity cannot be annotated with both @Entity and @MappedSuperclass: com.example1.demo1.Entity.User at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:493) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final] at org.hibernate.boot.model.source.internal.annotations.AnnotationMetadataSourceProcessorImpl.processEntityHierarchies(AnnotationMetadataSourceProcessorImpl.java:249) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final] at org.hibernate.boot.model.process.spi.MetadataBuildingProcess$1.processEntityHierarchies(MetadataBuildingProcess.java:222) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final] at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:265) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final] at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:861) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final] at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:888) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final] at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:57) ~[spring-orm-5.0.6.RELEASE.jar:5.0.6.RELEASE]
解決辦法：
在實例類上刪除掉@MappedSuperclass注解方可解決此錯誤，但是又會出現下面的錯誤：
No identifier specified for entity: com.example1.demo1.Entity.User
這個錯誤的原因是ID主鍵沒有聲明，程序找不到主鍵才報的錯誤。
但是有些情況下，刪除這個注解也有可能會報其他的異常，請參考下面這篇博客：
https://www.cnblogs.com/itiande/p/9139161.html