@Entity
@Table(name = "project_info")
public class Project {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private Integer project_id;

   private ProjectBasicInfo project_basic_info;

   @ElementCollection(targetClass = String.class)
   @CollectionTable(name = "project_extra_info", joinColumns = @JoinColumn(name = "project_id", nullable = false))
   @Column(name="extra_info_name")
   private List<String> project_extra_info = new LinkedList<String>();

   @ManyToMany(targetEntity=Student.class)
   @JoinTable(name="project22student",

      joinColumns=@JoinColumn(name="project_id"
         , referencedColumnName="project_id"),

      inverseJoinColumns=@JoinColumn(name="student_id"
         , referencedColumnName="student_id")
   )
   private Set<Student> stundet
      = new HashSet<Student>();

@Embeddable
public class ProjectBasicInfo {
   
   @Column(name="project_name", nullable=false)
   private String project_name;
   
   @Column(name="project_manager", nullable=false)
   private String project_manager;
   
   @Column(name="hoster")
   private   String hoster;
   @Parent
   private Project owner;
}

@Entity
@Table(name = "student_info")
public class Student {
   @Id
   @Column(name="student_id")
   private String student_id;
   
   private StudentBasicInfo student_basic_info;
   
   @ElementCollection(targetClass=String.class)
   @CollectionTable(name="student_project_info", joinColumns = @JoinColumn(name="student_id", nullable = false))
   @Column(name="extra_info_value", nullable=false)
   @MapKeyClass(StudentProjectInfoKey.class)
   private Map<StudentProjectInfoKey, String> studentProjectInfo = new HashMap<StudentProjectInfoKey, String>();
   
   @ManyToMany(targetEntity=Project.class)
   
   @JoinTable(name="project22student",
      
      joinColumns=@JoinColumn(name="student_id"
         , referencedColumnName="student_id"),
      
      inverseJoinColumns=@JoinColumn(name="project_id"
         , referencedColumnName="project_id")
   )
   private Set<Project> project
      = new HashSet<Project>();

@Embeddable
public class StudentBasicInfo {
   @Column(name="name")
   private String name;
   @Column(name="id")
   private String id;
   @Column(name="clazz")
   private String clazz;
   @Column(name="major")
   private String major;
   @Column(name="academy")
   private String academy;
   @Column(name="grade")
   private String grade;
   @Parent
   private Student owner;

@Embeddable
public class StudentProjectInfoKey {
   @Column(name="project_id")
   private Integer project_id;
   @Column(name="project_extra_info_name")
   private String project_extra_info_name;
   @Parent
   private Student owner;