Programmatically Modifying Components

In all examples you’ve seen so far, component property values are pulled in from a bean, like here:

<h:commandButton value="New" disabled="#{reportHandler.newDisabled}" />

I personally like this model, because it provides a clean separation between application logic and user interface components, but it’s not the only model supported by JSF. Some people are used to manipulating component properties programmatically instead. For instance, say you want to highlight an invalid value by turning the text in an input field red and adding a custom error message next to the field. To do so programmatically, you need references to the input component and the output component that holds the error message. Then you need to call the appropriate property setter method on the components.

The most convenient and easiest way to get a reference to a JSF component is using a component binding. A component binding is a special type of value binding that JSF uses to bind a component instance to a property in a bean. Here’s an example:

<%@ page contentType="text/html" %>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<f:view>
  <html>
    <body bgcolor="white">
      <h:form>
        Everything but "the kitchen sink": 
        <h:inputText validator="#{myBean.validateText}" />
        <h:outputText binding="#{myBean.errorComp}" />
        <br>
        <h:commandButton value="Test" />
      </h:form>
    </body>
  </html>
</f:view>

This page contains a form with ...

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