项目问SpringDataJpa项目，在运行的过程中出现的以下错误：
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]
解决办法：
在实例类上删除掉@MappedSuperclass注解方可解决此错误，但是又会出现下面的错误：
No identifier specified for entity: com.example1.demo1.Entity.User
这个错误的原因是ID主键没有声明，程序找不到主键才报的错误。
但是有些情况下，删除这个注解也有可能会报其他的异常，请参考下面这篇博客：
https://www.cnblogs.com/itiande/p/9139161.html