Business logic inside an accessor / getter method in JSF

Question

I have three tables in MySQL database.

• category (excluded from this question)
• sub_category
• product

The relationship between these tables is intuitive - one-to-many in the order in which they appear.

---

I'm iterating through a list of SubCategory, List<SubCategory> using <p:dataGrid> as follows.

<p:dataGrid var="row" value="#{featuredProductManagedBean}" rows="4" first="0" columns="1" rowIndexVar="rowIndex" paginator="true" paginatorAlwaysVisible="false" pageLinks="10" lazy="true" rowsPerPageTemplate="5,10,15">
    <h:panelGrid columns="1" style="width:100%;">
        <p:carousel value="#{featuredProductManagedBean.getProducts(row.subCatId)}" var="prodRow" numVisible="4" pageLinks="5" headerText="#{row.subCatName}" style="text-align: left;">

            <!--Display product image in <p:graphicImage>-->

        </p:carousel>
        <h:outputLink rendered="#{featuredProductManagedBean.count gt 4}" value="xxx">View More</h:outputLink>
    </h:panelGrid>

    <p:ajax event="page" onstart="PF('blockDataPanelUIWidget').block()" oncomplete="PF('blockDataPanelUIWidget').unblock()"/>
</p:dataGrid>

There is a parameterized getter method associated with the value attribute of </p:carousel> featuredProductManagedBean.getProducts(row.subCatId).

The method is called several times causing the expensive business service(s) to be invoked several times.

The managed bean:

@ManagedBean
@ViewScoped
public final class FeaturedProductManagedBean extends LazyDataModel<SubCategory> implements Serializable
{
    @EJB
    private final FeaturedProductBeanLocal service=null;
    private Product selectedProduct;  //Getter and setter.
    private Long count;               //Getter and setter.  
    private static final long serialVersionUID = 1L;

    public FeaturedProductManagedBean() {}

    public List<Product>getProducts(Long subCatId)
    {
        List<Product>products=null;

        if(FacesContext.getCurrentInstance().getCurrentPhaseId().getOrdinal()==6)
        {
            setCount(service.countProducts(subCatId));
            products=service.getProductList(subCatId);
        }

        return products;
    }

    @Override
    public List<SubCategory> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String, String> filters)
    {
        int rowCount = service.rowCount().intValue();
        setRowCount(rowCount);

        if(pageSize<=0)
        {
            FacesMessage message = new FacesMessage(FacesMessage.SEVERITY_FATAL, Utility.getMessage("faces.message.error"), Utility.getMessage("pageSize.error.message"));
            FacesContext.getCurrentInstance().addMessage(null, message);
            return Collections.emptyList();
        }
        else if(first>=pageSize&&rowCount<=Utility.currentPage(first, pageSize)*pageSize-pageSize) {
            first-=pageSize;
        }

        setPageSize(pageSize);
        return service.getList(first, pageSize);
    }
}

Neither @PostConstruct not lazy loading can be used here. Currently I have put a conditional check if(FacesContext.getCurrentInstance().getCurrentPhaseId().getOrdinal()==6) to prevent the service methods from being called multiple times. Does this conditional check perform the right thing? Does it have some side effects?

This answer maintains a Map but maintaining a Map for large data sources is expensive.

Is there a precise way to prevent such business logic from being executed multiple times?

Answer 1

I suggest to store the products of the currently loaded subCategory in a Map, just after they are loaded by the lazy model of <p:dataGrid>. The Map will never grow too much because you'll empty it at each invocation of the load method:

@ManagedBean
@ViewScoped
public final class FeaturedProductManagedBean extends LazyDataModel<SubCategory> implements Serializable
{
    @EJB
    private final FeaturedProductBeanLocal service=null;
    private Product selectedProduct;  //Getter and setter.
    private Long count;               //Getter and setter.  
    private Map<Long, Product> productsBySubCategory = new HashMap<>(); //Getter only.
    private static final long serialVersionUID = 1L;

    @Override
    public List<SubCategory> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String, String> filters)
    {
        int rowCount = service.rowCount().intValue();
        setRowCount(rowCount);

        List<SubCategory> subCategories = service.getList(first, pageSize);
        productsBySubCategory.clear();
        for (SubCategory sc : subCategories) 
        {
            productsBySubCategory.put(sc.getSubCatId(), service.getProductList(sc.getSubCatId());
        }
        return subCategories;
    }
}

And access directly the Map from EL:

<p:carousel value="#{featuredProductManagedBean.productsBySubCategory[row.subCatId]}" />

Note that you don't need all that boilerplate that checks page boundaries and sets pagesize.