Catch parsing exception during bean creation for @RequestParameter in Seam 2.2.2

Question

I have a simple java bean which uses request parameters for property initialization. For this, seam provides a convenient @RequestParameter annotation which injects the request parameter directly in a bean property which is great except for error handling. Is there any way to catch parsing exceptions (NumberFormatException, ...) if the request parameters are broken to provide a more user friendly error output?

I'm aware of exception handling in pages.xml but I don't want to put a NumberFormatException there, as it is way to generic without further context.

Minimal example for a bean, where parsing exceptions for entityId should be caught:

@Name("apiPresenter")
@Scope(ScopeType.PAGE)
public class MyBean {

  @RequestParameter
  private Long entityId;
  ...
}

Answer 1

@RequestParameter is handy sometimes but is not very flexible. When you need to map parameters that require conversion and/or validation, it is adviced to use page parameter definitions, as these let you specify a JSF converter or validator to apply during parameter decoding, for example:

<page view-id="/myview.xthml">
  <param name="entityId" value="#{apiPresenter.entityId}" converterId="javax.faces.Long" />
</page>

If there are conversion or validation errors, the converter adds a message to the JSF FacesMessages component, which can be used to render the error condition in an error page. Note that you can use your own converters and/or validators here, you can even indicate that a parameter is required, as in:

<page view-id="/myview.xhtml">
  <!-- parameter is required, issue error if it is not provided -->
  <param name="entityId" value="#{apiPresenter.entityId}" validatorId="your.validator" required="true" />
</page>

Alternatively, you can use @RequestParameter to assign the parameter to a String variable and then perform the conversion (and eventual redirection to an error page) by hand.