I was working with spring 4 integration with hibernate 4 and encountered and error:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory' defined in ...CustomConfiguration: Invocation of init method failed; nested exception is org.hibernate.AnnotationException: No identifier specified for entity: ...

I was trying to load a table user with primary key Id. While I marked the id as @Id i was still getting the above error.       

    @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 @Column(name = "id", unique = true, nullable = false)
 public int getId() {
  return this.id;
 }

Solution:

Always add

import javax.persistence.Id;

Not to use :

import org.springframework.data.annotation.Id;