как сравнить, чтобы избежать вставки повторяющихся данных в arraylist

у меня есть класс, в котором я вставляю данные в список массивов на основе предоставленного идентификатора. Я передаю bookId в свой класс и, сравнивая bookid, получаю объект книги. И после получения этого объекта (книги) я вставляю его в свой массив. Теперь я не хочу вставлять одни и те же данные более одного раза. Если в классе проходит один и тот же идентификатор книги, то он должен храниться только один раз.
Я сохраняю свой список массивов в сеансе.

пожалуйста, проверьте мой код. И предложите мне решение моей проблемы.Как избежать повторной вставки данных в мой arraylist?

Аддбуктосессион.java

   ..................
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    ...................
    private Integer bid;  HttpServletRequest request = ServletActionContext.getRequest();  
    private Map<String, Object> session; 
    List<Bookdetails> books = new ArrayList<Bookdetails>();
    private BookdetailsDAO dao = new BookdetailsDAO(); 

    public String execute() 
    {  
           String bookid = request.getParameter("bid");    
        Bookdetails book = dao.listBookDetailsById(Integer.parseInt(bookid));
        int checkduplicate=1;

           //getting list from session to compare with the id
        List list = (List) session.get( VisionBooksConstants.USER );  
           Iterator itr = list.iterator(); 
           int bidd=0;

        while(itr.hasNext())
        { 
            Bookdetails bks=(Bookdetails) itr.next();
            bidd=bks.getId(); //getting bookid from arraylist,which was stored in session
            if (bidd==Integer.parseInt(bookid))
            {
           checkduplicate=0; //returns 0 ,so that i can compare it below to avoid duplicate data
         }
        }
         //
        if (book != null && checkduplicate==1  ) 
        { 
            books = sessionBooks();
            HttpServletRequest request = ServletActionContext.getRequest();  
            books.add(book);
            System.out.println("books size"+books.size()); 
        }

        return SUCCESS;
    } 
       ........................
        ...................... 

Альтернативное решение обновление HashSet()

  public String execute() 
    {    HashSet<Bookdetails> books = new HashSet<Bookdetails>();
          String bookid = request.getParameter("bid");    
          Bookdetails book = dao.listBookDetailsById(Integer.parseInt(bookid));
          books =  (HashSet<Bookdetails>) session.get(BillTransactionBooksConstants.BOK);
          if ( books == null ) books = new HashSet<Bookdetails>();
           boolean already_exists = false; 
            books.add(book);
            System.out.println("books size"+books.size()); 
            session.put(BillTransactionBooksConstants.BOK,books);

        return SUCCESS;
    } 

Bookdetails.java(Pojo)

        package v.esoft.pojos;

    // Generated Nov 5, 2012 9:37:14 PM by Hibernate Tools 3.4.0.CR1

    import java.util.Date;
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import static javax.persistence.GenerationType.IDENTITY;
    import javax.persistence.Id;
    import javax.persistence.Table;
    import javax.persistence.Temporal;
    import javax.persistence.TemporalType;


    /**
     * Bookdetails generated by hbm2java
     */
    @Entity
    @Table(name = "bookdetails", catalog = "vbsoftware")
    public class Bookdetails implements java.io.Serializable {

        private Integer id;
        private String isbn;
        private String bookTitile;
        private String authFirstname;
        private String authLastname;
        private String editionYear;
        private Integer subjectId;
        private Integer coverId;
        private Integer languageId;
        private String publisherName;
        private Integer editionId;
        private Float price;
        private String quantity;
        private String description;
        private Integer locationId;
        private String remarks;
        private String img1;
        private String img2;
        private String videoUrl;
        private Integer createrId;
        private Date createdDate;
        private Integer updateId;
        private Date updatedDate;

        public Bookdetails() {
        }

        public Bookdetails(String isbn, String bookTitile, String authFirstname,
                String authLastname, String editionYear, Integer subjectId,
                Integer coverId, Integer languageId, String publisherName,
                Integer editionId, Float price, String quantity,
                String description, Integer locationId, String remarks,
                String img1, String img2, String videoUrl, Integer createrId,
                Date createdDate, Integer updateId, Date updatedDate) {
            this.isbn = isbn;
            this.bookTitile = bookTitile;
            this.authFirstname = authFirstname;
            this.authLastname = authLastname;
            this.editionYear = editionYear;
            this.subjectId = subjectId;
            this.coverId = coverId;
            this.languageId = languageId;
            this.publisherName = publisherName;
            this.editionId = editionId;
            this.price = price;
            this.quantity = quantity;
            this.description = description;
            this.locationId = locationId;
            this.remarks = remarks;
            this.img1 = img1;
            this.img2 = img2;
            this.videoUrl = videoUrl;
            this.createrId = createrId;
            this.createdDate = createdDate;
            this.updateId = updateId;
            this.updatedDate = updatedDate;
        }

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

        public void setId(Integer id) {
            this.id = id;
        }


        //########################################################################### 
                        //  FOR HASHSETS EQUALS
        //########################################################################### 
        public Bookdetails(int i){ id = i; }

        public boolean equals(Object obj){
            System.err.println("called"); // Never happens
            return id == ((Bookdetails)obj).id;
        }


        @Column(name = "isbn", length = 90)
        public String getIsbn() {
            return this.isbn;
        }

        public void setIsbn(String isbn) {
            this.isbn = isbn;
        }

        @Column(name = "book_titile")
        public String getBookTitile() {
            return this.bookTitile;
        }

        public void setBookTitile(String bookTitile) {
            this.bookTitile = bookTitile;
        }

        @Column(name = "auth_firstname", length = 120)
        public String getAuthFirstname() {
            return this.authFirstname;
        }

        public void setAuthFirstname(String authFirstname) {
            this.authFirstname = authFirstname;
        }

        @Column(name = "auth_lastname", length = 120)
        public String getAuthLastname() {
            return this.authLastname;
        }

        public void setAuthLastname(String authLastname) {
            this.authLastname = authLastname;
        }

        @Column(name = "edition_year", length = 20)
        public String getEditionYear() {
            return this.editionYear;
        }

        public void setEditionYear(String editionYear) {
            this.editionYear = editionYear;
        }

        @Column(name = "subject_id")
        public Integer getSubjectId() {
            return this.subjectId;
        }

        public void setSubjectId(Integer subjectId) {
            this.subjectId = subjectId;
        }

        @Column(name = "cover_id")
        public Integer getCoverId() {
            return this.coverId;
        }

        public void setCoverId(Integer coverId) {
            this.coverId = coverId;
        }

        @Column(name = "language_id")
        public Integer getLanguageId() {
            return this.languageId;
        }

        public void setLanguageId(Integer languageId) {
            this.languageId = languageId;
        }

        @Column(name = "publisher_name", length = 70)
        public String getPublisherName() {
            return this.publisherName;
        }

        public void setPublisherName(String publisherName) {
            this.publisherName = publisherName;
        }

        @Column(name = "edition_id")
        public Integer getEditionId() {
            return this.editionId;
        }

        public void setEditionId(Integer editionId) {
            this.editionId = editionId;
        }

        @Column(name = "price", precision = 12, scale = 0)
        public Float getPrice() {
            return this.price;
        }

        public void setPrice(Float price) {
            this.price = price;
        }

        @Column(name = "quantity", length = 40)
        public String getQuantity() {
            return this.quantity;
        }

        public void setQuantity(String quantity) {
            this.quantity = quantity;
        }

        @Column(name = "description", length = 65535)
        public String getDescription() {
            return this.description;
        }

        public void setDescription(String description) {
            this.description = description;
        }

        @Column(name = "location_id")
        public Integer getLocationId() {
            return this.locationId;
        }

        public void setLocationId(Integer locationId) {
            this.locationId = locationId;
        }

        @Column(name = "remarks", length = 65535)
        public String getRemarks() {
            return this.remarks;
        }

        public void setRemarks(String remarks) {
            this.remarks = remarks;
        }

        @Column(name = "img1")
        public String getImg1() {
            return this.img1;
        }

        public void setImg1(String img1) {
            this.img1 = img1;
        }

        @Column(name = "img2")
        public String getImg2() {
            return this.img2;
        }

        public void setImg2(String img2) {
            this.img2 = img2;
        }

        @Column(name = "video_url", length = 65535)
        public String getVideoUrl() {
            return this.videoUrl;
        }

        public void setVideoUrl(String videoUrl) {
            this.videoUrl = videoUrl;
        }

        @Column(name = "creater_id")
        public Integer getCreaterId() {
            return this.createrId;
        }

        public void setCreaterId(Integer createrId) {
            this.createrId = createrId;
        }

        @Temporal(TemporalType.TIMESTAMP)
        @Column(name = "created_date", length = 19)
        public Date getCreatedDate() {
            return this.createdDate;
        }

        public void setCreatedDate(Date createdDate) {
            this.createdDate = createdDate;
        }

        @Column(name = "update_id")
        public Integer getUpdateId() {
            return this.updateId;
        }

        public void setUpdateId(Integer updateId) {
            this.updateId = updateId;
        }

        @Temporal(TemporalType.TIMESTAMP)
        @Column(name = "updated_date", length = 19)
        public Date getUpdatedDate() {
            return this.updatedDate;
        }

        public void setUpdatedDate(Date updatedDate) {
            this.updatedDate = updatedDate;
        }

    }