@Entity(name = "Comment")
@Table(name = "tbl_comment")
public class CommentBean implements Serializable {

	@Id
	@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_comment_id")
	@SequenceGenerator(name = "seq_comment_id", sequenceName = "seq_comment_id", allocationSize = 1)
	private Long id = null;

  ...
}


@Entity(name = "Product")
@Table(name = "tbl_product")
public class CommentBean implements Serializable {

	@Id
	@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_product_id")
	@SequenceGenerator(name = "seq_product_id", sequenceName = "seq_product_id", allocationSize = 1)
	private Long id = null;

@ManyToMany(cascade = CascadeType.MERGE)
	@JoinTable(name = "tbl_product_comments", joinColumns = {
			@JoinColumn(name = "product_id", referencedColumnName = "id") }, inverseJoinColumns = {
					@JoinColumn(name = "comment_id", referencedColumnName = "id") }, uniqueConstraints = {
							@UniqueConstraint(columnNames = { "product_id", "comment_id" }) })
	@IndexedEmbedded
	@OrderBy(value = "createdDate ASC")
	private Set<CommentBean> comments = new LinkedHashSet<>();

  ...
}

@Entity(name = "ProductComment")
@Table(name = "tbl_product_comments")
public class ProductCommentBean implements Serializable {

	private static final long serialVersionUID = 4730115318809856150L;

	@ManyToOne(optional = false)
	@JoinColumn(name = "productID", referencedColumnName = "id", nullable = false, insertable = false, updatable = false)
	@NotNull
	private ProductBean answer = null;

	@ManyToOne(optional = false)
	@JoinColumn(name = "comment_id", referencedColumnName = "id", nullable = false, insertable = false, updatable = false)
	@NotNull
	private CommentBean comment = null;

	@EmbeddedId
	private ID id = new ID();

	@Embeddable
	public static class ID implements Serializable {

		@Column(name = "product_id")
		private Long productID = null;

		@Column(name = "comment_id")
		private Long commentID = null;

		@Override
		public boolean equals(final Object other) {
			if (this == other) {
				return true;
			}
			if (!(other instanceof ID)) {
				return false;
			}
			ID castOther = (ID) other;
			return new EqualsBuilder().append(productID, castOther. productID).append(commentID, castOther.commentID)
					.isEquals();
		}

		@Override
		public int hashCode() {
			return new HashCodeBuilder(-2081682373, -1619249).append(productID).append(commentID).toHashCode();
		}

		public ID() {
			super();
			// TODO Auto-generated constructor stub
		}

		public ID(Long productID, Long commentID) {
			super();
			this.productID = productID;
			this.commentID = commentID;
		}

	}

	public ProductCommentBean(ProductBean product, CommentBean comment) {
		super();
		this.product = product;
		this.comment = comment;

		this.id.productID =product.getId();
		this.id.commentID = comment.getId();
             }
	}

  ...
}