UISelectOne

UISelectOne is a user interface component used in JavaServer Faces (JSF) to allow a user to select a single value from a set of choices. The component is defined by the javax.faces.component.UISelectOne class and is typically rendered as a drop‑down menu, radio buttons, or a custom widget depending on the chosen renderer. It serves as the basis for the <h:selectOneMenu>, <h:selectOneRadio>, and <h:selectOneListBox> tag families in the standard JSF component library.

The UISelectOne component inherits from the UIInput base class, accepting a single submitted value and converting it into a Java object via the JSF conversion and validation framework. Developers can add validators and converters to enforce constraints or transform input data. When rendering, the component consults its children UISelectItem or UISelectItemGroup elements to generate the list of available options. The component also supports dynamic population of options through value expressions that return a Collection, Map, or array of objects.

In tag library usage, the value attribute binds the selected value to a backing bean property, while the "label" attribute can be used for accessibility. Developers often pair UISelectOne with a f:selectItems tag to supply options from a list or enum. When localization is required, the javax.faces.component.UISelectOne implements the LocalizedProperties interface, allowing action components such as value changes to be internationalized.

The component's life cycle is integrated with JSF’s per-request processing model: during the APPLY_REQUEST_VALUES phase the submitted value is stored; during PROCESS_VALIDATIONS, the component’s validators run; and during UPDATE_MODEL_VALUES, the new value is written back to the backing bean. This design enables efficient data binding and validation in web applications.