About Conversion and Validation Errors

When a conversion or validation error occurs, the component whose conversion or validation failed places an error message in the queue and invalidates itself. After the Process Validations phase, JSF redisplays the current page.

To let the user know what caused the conversion or validation error, you need to display the error message next to the component that generated the message. To do this, you must assign an ID to the component. Then use the h:message tag next to the component, referencing the component's ID in the tag's for attribute. You can specify whether to display a detail message (default) or a summary message.

If you want to change the text of the standard converter message, you can set up a message bundle and supply the replacement text for the conversion failed message, using the key javax.faces.component.UIInput.CONVERSION.

[can you do the same for validation errors? what is the key for validation?]

Note: It is possible but uncommon for a component to report more than one message. In this unlikely event, the h:message tag shows only the first message generated by the component. For debugging purposes, use the h:messages tag on a page to see all messages generated by all components.