Empty Test for String Values using Expression Language

On the OTN ADF & JDeveloper space (aka forum) I often read use cases where an action depends on the state of an af:inputText, or better the value entered in the component.
This is problematic as a String value can either be null or it can be empty. The problem is that is you want to test a String value using Expression Language (EL) in the UI, you can’t use e.g.

#{bindings.myText1.inputValue eq ''}

The solution is an existing, but mostly unknown operator of Expression Language (EL) called ’empty’. This operator checks a String value if it’s empty. Usage of the operator is a bit different from the other operators which are used after the value. The ’empty’ operator is used in front of the valeu like

#{empty bindings.myText1.inputValue}

consider the following use case: a button should be enabled only if a inputText component is not empty. For this we can use this code

            <af:panelGroupLayout layout="scroll" xmlns:af="http://xmlns.oracle.com/adf/faces/rich" id="pgl1">
              <af:inputText label="Label 1" id="it1" value="#{bindings.myText1.inputValue}" autoSubmit="true"/>
              <af:commandButton text="commandButton 1" id="cb1" disabled="#{empty bindings.myText1.inputValue}" partialTriggers="it1"/>
              <af:outputText value="Working (empty bindings.myText1.inputValue): #{empty bindings.myText1.inputValue} --- not working(bindings.myText1.inputValue eq '': #{bindings.myText1.inputValue eq ''}" id="ot1"

As you see, the af:inputText component stored it’s value in a pageDef variable (or a VO row) and submits the entered value using the autoSubmit property set to ‘true’. The af:commandButton gets enabled only if the EL
#{empty bindings.myText1.inputValue}
returns false. This is the case when you enter anything into the af:inputText. The final piece to make it work is the partial trigger on the af:button component listening to the change of the input value.
The outputText below the button is just to show that the EL
#{bindings.myText1.inputValue eq ''}
does not work correctly.

4 thoughts on “Empty Test for String Values using Expression Language

    • As I already said, it’s not always the same. If you have a string which is initialized with “” (empty string), the ‘eq null’ returns false as the string is not null. In this case only the ’empty’ works. Empty returns true if the string is null or has the length 0.

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