Session scoped beans and @PostConstruct in JSF

Question

A quite simple and straight-forward question.

I have a session scoped managed bean as follows (demonstrating a PrimeFaces range slider).

@ManagedBean
@SessionScoped
public final class RangeSliderBean implements Serializable
{
    private static final long serialVersionUID = 1L;
    private static final byte scale=2;

    private BigDecimal maxPrice;
    private BigDecimal minPrice;

    public RangeSliderBean()
    {
        maxPrice=new BigDecimal(100).setScale(scale, RoundingMode.HALF_UP);
        minPrice=new BigDecimal(5).setScale(scale, RoundingMode.HALF_UP);
    }

    @PostConstruct
    private void init()
    {

    }

    //Mutators and accessors
}

The given two fields in the above session scoped managed bean are bound to an XHTML page.

<h:form id="rangeForm" prependId="true">
    <p:panel header="Shop by Price">
        <h:panelGrid id="rangeSliderPanelGrid" columns="1" style="margin-bottom:10px">
            <h:outputText id="displayRange" value="Min : #{rangeSliderBean.minPrice.toPlainString()} Max : #{rangeSliderBean.maxPrice.toPlainString()}"/>

            <p:slider for="txtMinPrice, txtMaxPrice" 
                      minValue="#{rangeSliderBean.minPrice}" 
                      maxValue="#{rangeSliderBean.maxPrice}" 
                      display="displayRange" 
                      style="width:170px" 
                      range="true" displayTemplate="Min : {min} Max : {max}"/>
        </h:panelGrid>

        <h:inputHidden id="txtMinPrice" value="#{rangeSliderBean.minPrice}" converter="#{bigDecimalConverter}"/>
        <h:inputHidden id="txtMaxPrice" value="#{rangeSliderBean.maxPrice}" converter="#{bigDecimalConverter}"/>
        <p:commandButton value="Submit"/> <!--Update/process is temporarily omitted.-->
    </p:panel>
</h:form>

If these fields are initialized in the method annotated by @PostConstruct i.e init(), in this case (instead of initializing them in the constructor as shown in the snippet), their specified values are not set unless and until a user logs in (unless a session is created).

How can they be initialized in the constructor then, just a little confusion? (I know that the constructor is called before the method annotated by @PostConstruct is invoked).

Answer 1

How can they be initialized in the constructor then, just a little confusion? (I know that the constructor is called before the method annotated by @PostConstruct is invoked).

Use the @PostConstruct's init method only to initialize fields which are being injected (i.e Ejbs). If you don't have any injections and dependencies, init method becomes pretty useless. The bean's constructor is used to initialize bean's own properties. In your example, you don't have any injection, so you can safely remove that @PostConstruct's init method.

If these fields are initialized in the method annotated by @PostConstruct i.e init(), in this case (instead of initializing them in the constructor as shown in the snippet), their specified values are not set unless and until a user logs in (unless a session is created).

It's the normal behavior, there is no reason to emphasize on the not, because a @SessionScoped bean is created and initialized only when a new session is created.

For more info check the link, the question has already been answered : Why use @PostConstruct?