Full tutorial here: https://cedricleruth.com/how-to-set-a-binding-value-on-a-button-click-in-jsf-and-oracle-adf/

SetBindingValueOnButtonClick.xml

<!-- use xmlns:f="http://java.sun.com/jsf/core" in the f:view at the top of your jsf file -->
<!-- e.g: <f:view xmlns:f="http://java.sun.com/jsf/core" xmlns:af="http://xmlns.oracle.com/adf/faces/rich" -->

<!-- Here's how to set binding values one a button click - useful when you want to set values right before commiting a user form -->
<af:commandButton text="YOUR_BUTTON" id="bid1" action="#{YOUR_SCOPE.YOUR_BEAN.YOUR_ACTION_FUNC}">
    <!-- You can either set a custom value YOUR_VALUE or the value of another binding #{bindings.YOUR_SOURCE_BINDING.inputValue} -->
    <!-- or even the value of an attribute of YOUR_BEAN with getter and setter generated-->
    <f:setPropertyActionListener value="YOUR_VALUE" target="#{bindings.YOUR_TARGET_BINDING1.inputValue}"/>
    <f:setPropertyActionListener value="#{bindings.YOUR_SOURCE_BINDING.inputValue}" target="#{bindings.YOUR_TARGET_BINDING2.inputValue}"/>
    <f:setPropertyActionListener value="#{YOUR_SCOPE.YOUR_BEAN.YOUR_ATTRIBUTE}" target="#{bindings.YOUR_TARGET_BINDING3.inputValue}"/>
</af:commandButton>