Sample Store Catalog Application using Visual Web Pack and the Java Persistence APIs

   
    private Item item; 
    private int firstItem = 0;
    private int size=0;
    private int lastBatchItem=0;
    private int batchIndex=0;
    private int index=0;
    private List items=null;
    private int batchSize = 10;
    @PersistenceUnit(unitName = "vwp-sessionpaginationPU")
    private EntityManagerFactory emf;
    
    private EntityManager getEntityManager() {
        return emf.createEntityManager();
    }
    public Item getItem() {
        return item;
    }
    
    public void setItem(Item item) {
        this.item = item;
    }
    public Item findItem(String id) {
        EntityManager em = getEntityManager();
        try{
            item = (Item) em.find(Item.class, id);
            return item;
        } finally {
            em.close();
        }
    }
    


    public int getIndex() {
        return this.index;
    }
    public void setIndex(int index) {
        this.index = index;
    }
    public Item getItem(int index){
        items=getItems();
        if( index >= firstItem)
            batchIndex= index-firstItem;
        else if( firstItem < batchSize){
            batchIndex= firstItem;
        }
        if (batchIndex>=batchSize) batchIndex=batchSize-1;
        item=items.get(batchIndex);
        return item;
    }
    
    public List getItems(){
        if (items==null || items.isEmpty() ){
            items = getItems( firstItem,batchSize);
        }
        return this.items;
    }
    
    public List getNextItems() {
        if (size > batchSize) {
            items = getItems( firstItem,batchSize);
        }
        return this.items;
    }
    public List  getItems(int firstItem,int batchSize) {
        EntityManager em = getEntityManager();
        try{
            Query q = em.createQuery("select object(o) from Item as o");
            q.setMaxResults(batchSize);
            q.setFirstResult(firstItem);
            items=q.getResultList();
            return items;
        } finally {
            em.close();
        }
    }
    public int getItemCount() {
        EntityManager em = getEntityManager();
        try{
            int count = ((Long) em.createQuery("select count(o) from Item as o").getSingleResult()).intValue();
            return count;
        } finally {
            em.close();
        }
    }
    public void setItem(int index) {
        item=getItem(index);
    }
    public int getFirstItem() {
        index=firstItem;
        return firstItem;
    }
    public void first() {
        firstItem=0;
        index=firstItem;
        getNextItems();
    }
    public void last() {
        firstItem=size-batchSize;
        index=size-1;
        getNextItems();
    }
    
    public int getLastBatchItem() {
        lastBatchItem= firstItem + batchSize > size ? size : firstItem + batchSize;
        lastBatchItem--;
        return lastBatchItem;
    }
    public int getBatchSize() {
        return batchSize;
    }
    public void nextBatch() {
        if (firstItem + batchSize < getItemCount()) {
            firstItem += batchSize;
            index=firstItem;
            getNextItems();
        } else{
            index=getLastBatchItem();
        }
    }
    
    public void prevBatch() {
        firstItem -= batchSize;
        if (firstItem < 0) {
            firstItem = 0;
        }
        index=firstItem;
        getNextItems();
    }
    public void next() {
        if (index < size) {
            index++;
        }
        if (index > firstItem + batchSize) {
            nextBatch();
        }
    }
    
    public void prev() {
        if (index>0){
            index--;
        }
        if (index < firstItem) {
            prevBatch();
        }
    }

 
 public void init() {
  . . .
 
  
       items=getItems();
       size = getItemCount();
       if (size < batchSize){
           batchSize=size;
       }
       setItem(firstItem);

  }