displaying values from database on the basis of dropdown menu selction

Question

hi i am creating a JSF application . In fact I made a dropdown list and want to display the results according to the value selected from the dropdown. if somebody can help.... thanks

here is my drop down

<h:form>
                <h:commandButton action="sample?faces-redirect=true" value="submit">
                    <h:selectOneMenu id="sampleSearch" value="#{cBean.id}">
                    <f:selectItem id="id" itemLable="idText" itemValue="By Text" />
                    <f:selectItem id="idnumeric" itemLable="idNumeric" itemValue="Number" />
                    <f:selectItem id="product" itemLable="Product" itemValue="Main Product" />
                    <f:selectItem id="lonumber" itemLable="loNumber" itemValue="LoNumber" />
                    <f:selectItem id="formula" itemLable="formula" itemValue="By Formula" />
                    </h:selectOneMenu>
                </h:commandButton>

            </h:form>

noone · Answer 1 · 2013-08-26T13:30:51.660

I advice you to read a book about JSF or at least some more tutorials about it. Your code makes not much sense. You nest a selectOneMenu inside of a commandButton. And if you want to display some values from your database, you should also call a method in your managed bean to do the query and retrieve the results.

That's how you should do it instead:

<h:form>
    <h:selectOneMenu id="sampleSearch" value="#{cBean.id}">
        <f:selectItem id="id" itemLable="idText" itemValue="By Text" />
        <f:selectItem id="idnumeric" itemLable="idNumeric" itemValue="Number" />
        <f:selectItem id="product" itemLable="Product" itemValue="Main Product" />
        <f:selectItem id="lonumber" itemLable="loNumber" itemValue="LoNumber" />
        <f:selectItem id="formula" itemLable="formula" itemValue="By Formula" />
    </h:selectOneMenu>
    <h:commandButton action="#{cBean.search}" value="submit" />
</h:form>

And your bean would look like this:

public class CBean {
    private String id; // getter+setter

    public String search() {
        // perform your query based on the id value

        return "sample?faces-redirect=true";
    }
}

score 1 · Accepted Answer · edited May 23 '17 at 12:05

First, you're not allowed to nest <h:selectOneMenu> component(s) within <h:commandButton>! Here's a proper structure of your <h:form>

<h:form>
    <h:commandButton action="sample?faces-redirect=true" value="submit" />
        <h:selectOneMenu id="sampleSearch" value="#{cBean.id}">
            <f:selectItem id="id" itemLable="idText" itemValue="By Text" />
            <f:selectItem id="idnumeric" itemLable="idNumeric" itemValue="Number" />
            <f:selectItem id="product" itemLable="Product" itemValue="Main Product" />
            <f:selectItem id="lonumber" itemLable="loNumber" itemValue="LoNumber" />
            <f:selectItem id="formula" itemLable="formula" itemValue="By Formula" />
    </h:selectOneMenu>
</h:form>

Then, in order to get the dropdown list options from the database, you can consider using the <f:selectItems> component (and get rid of those <f:selectItem>s) and pass a List<T> from the managed bean to the components value property.

The selectOneMenu would then look like this:

<h:selectOneMenu value="#{cBean.id}">
    <f:selectItems value="#{cBean.values}" 
                   var="item"
                   itemLabel="#{item.label}"
                   itemValue="#{item.value}"/>
</h:selectOneMenu>

As for the managed-bean, it's now supposed to provide a public List<T> getValues() method, which will return a list with the objects that will populate the dropdown.

When T is a complex Java object, such as Item which has a String property of label and value, then you could use the var attribute to get hold of the iteration variable which you in turn can use in itemValue and/or itemLabel attribtues (if you omit the itemLabel, then the label becomes the same as the value).

Let's say:

@ManagedBean
@RequestScoped
public class CBean {
    public List<Item> getValues() {
        List<Item> result = new ArrayList<Item>();
        //..call-back to web-service, db, etc. and populate the result variable.
        return result;
    }
}

The Item class would look like this:

public class Item {
   private String label;
   private String value;

   //getters, setters.
}

You can read more here:

How to prepopulate a from a DB?

You forgot to mention that in case he uses a complex type like `Item` in your case, he also has to write a custom `ItemConverter`. — noone, Aug 26 '13 at 13:30
`Item` has two `String` properties (which are used as item and label), so there's no need of `ItemConverter`. In the cases in which the itemValue property holds the whole variable (like `itemValue="#{item}`) then a `Converter` is needed, because the `Item` object has to be represented as a `String`. — Konstantin Yovkov, Aug 26 '13 at 13:35

displaying values from database on the basis of dropdown menu selction

2 Answers2