Performing a redirect, when conversion / validation associated with query parameters fails

Question

The following is a simple use case of .

Answer 1

This is specified behavior. When PROCESS_VALIDATIONS phase ends with a validation failure, both the UPDATE_MODEL_VALUES and INVOKE_APPLICATION phases are skipped. Exactly like as in "regular" forms with . Think of as a and a as a and it will become more clear.

For your particular requirement, performing a redirect when conversion/validation has failed, there are at least 3 solutions:

1. As you found out, add a . I'd rather hook on postValidate event instead for better self-documentability.

   public void redirectIfNecessary() throws IOException {
       FacesContext context = FacesContext.getCurrentInstance();
   
       if (!context.isPostback() && context.isValidationFailed()) {
           context.getExternalContext().redirect("some.xhtml");
       }
   }
   

   The check on FacesContext#isPostback() prevents the redirect being performed on validation failures of "regular" forms in the same view (if any).

   ---

2. Extend the builtin LongConverter whereby you perform the redirect in getAsObject() (a validator is insuitable as the default converter for Long would already fail on non-numeric inputs; if a converter fails, the validators are never fired). This is however poor design (tight-coupling).

   @FacesConverter("idConverter")
   public class IdConverter extends LongConverter {
   
       @Override
       public Object getAsObject(FacesContext context, UIComponent component, String value) {
           if (value == null || !value.matches("[0-9]{1,20}")) {
               try {
                   context.getExternalContext().redirect("some.xhtml");
                   return null;
               }
               catch (IOException e) {
                   throw new FacesException(e);
               }
           }
           else {
               return super.getAsObject(context, component, value);
           }
       }
   
   }
   

   You could if necessary play around with inside to "pass" parameters to the converter.

   String redirect = (String) component.getAttributes().get("redirect");
   context.getExternalContext().redirect(redirect);
   

   ---

3. Create a custom taghandler which does basically the same as but without the need for an additional backing bean method.

   com.example.taghandler.ViewParamValidationFailed

   public class ViewParamValidationFailed extends TagHandler implements ComponentSystemEventListener {
   
       private String redirect;
   
       public ViewParamValidationFailed(TagConfig config) {
           super(config);
           redirect = getRequiredAttribute("redirect").getValue();
       }
   
       @Override
       public void apply(FaceletContext context, UIComponent parent) throws IOException {
           if (parent instanceof UIViewRoot && !context.getFacesContext().isPostback()) {
               ((UIViewRoot) parent).subscribeToEvent(PostValidateEvent.class, this);
           }
       }
   
       @Override
       public void processEvent(ComponentSystemEvent event) throws AbortProcessingException {
           FacesContext context = FacesContext.getCurrentInstance();
   
           if (context.isValidationFailed()) {
               try {
                   context.getExternalContext().redirect(redirect);
               }
               catch (IOException e) {
                   throw new AbortProcessingException(e);
               }
           }
       }
   
   }
   

   /WEB-INF/my.taglib.xml

   
   
       http://example.com/ui
   
       
           viewParamValidationFailed
           com.example.taghandler.ViewParamValidationFailed
         
   
   

   /WEB-INF/web.xml

   
       javax.faces.FACELETS_LIBRARIES
       /WEB-INF/my.taglib.xml
   
   

   True, it's a bit of code, but it ends up in clean and reusable tag and is actually a good fit for a new OmniFaces feature.