ProjectAssociation.java

@Entity
@Table(name="PROJ_EMP")
@IdClass(ProjectAssociationId.class)
public class ProjectAssociation {
  @Id
  private long employeeId;
  @Id
  private long projectId;
  @Column("IS_PROJECT_LEAD")
  private boolean isProjectLead;
  @ManyToOne
  @PrimaryKeyJoinColumn(name="EMPLOYEEID", referencedColumnName="ID")
  private Employee employee;
  @ManyToOne
  @PrimaryKeyJoinColumn(name="PROJECTID", referencedColumnName="ID")
  private Project project;

//[...]

}