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?

In order to prevent the business logic being executed several times you should move it out of the getter and place in a PostConstruct method. It's not clear why you say you can't. — perissf, Apr 02 '14 at 05:45
possible duplicate of [Primefaces dataTable call method multiple times when click commandButton. why?](http://stackoverflow.com/questions/22662276/primefaces-datatable-call-method-multiple-times-when-click-commandbutton-why) — Danubian Sailor, Apr 02 '14 at 06:50
Because it is presumably not possible using [criteria/JPQL](http://stackoverflow.com/q/22523074/1391249), @perissf — Tiny, Apr 02 '14 at 10:28
If a query is not doable with JPA there are many workarounds simpler than what you are trying to do: changing the db schema, splitting the query into trunks and handling the trunks in java, etc... If I were you I'd avoid if possible to increase complexity in the app just for this reason. But obviously I don't know all the business requirements of your app... — perissf, Apr 02 '14 at 11:14
This is just an attempt to split a query into chunks as you said, @perissf — Tiny, Apr 02 '14 at 11:18

score 1 · Accepted Answer · edited Apr 02 '14 at 19:08

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.

Business logic inside an accessor / getter method in JSF

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