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

Question

The following is a simple use case of <f:viewAction>.

<f:metadata>
    <f:viewParam name="id" value="#{testManagedBean.id}" maxlength="20"/>
    <f:viewAction action="#{testManagedBean.viewAction}"/>
</f:metadata>

The managed bean involved.

@ManagedBean
@ViewScoped
public final class TestManagedBean implements Serializable {

    private static final long serialVersionUID = 1L;
    private Long id; //Getter and setter.

    public void viewAction() {
        System.out.println("viewAction() called : " + id);
    }
}

The parameter id is passed through a URL. There is a conversion error, when a non-numeric value like xxx is passed through the URL in question and the viewAction() method associated with the listener of <f:viewAction> is not invoked.

The value of id is null in this case. I would like to redirect to another page, when id is not convertible to a desired target type (like in this case) or id is not validated against the specified validation criteria to avoid potential exceptions which are likely to be thrown in the LazyDataModel#load() method of PrimeFaces or somewhere else in the associated managed bean whenever access to these parameters is attempted in the corresponding managed bean. For this to be so, the viewAction() method should be invoked.

How to proceed with this? Should I use

<f:event type="preRenderView">

in conjunction with <f:viewAction>?

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 <h:form>. Think of <f:viewParam> as a <h:inputText> and a <f:viewAction> as a <h:commandButton> 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 <f:event listener>. I'd rather hook on postValidate event instead for better self-documentability.

   <f:metadata>
       <f:viewParam name="id" value="#{bean.id}" maxlength="20" />
       <f:event type="postValidate" listener="#{bean.redirectIfNecessary}" />
       <f:viewAction action="#{bean.viewAction}" />
   </f:metadata>
   

   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).

   <f:metadata>
       <f:viewParam name="id" value="#{bean.id}" converter="idConverter" />
       <f:viewAction action="#{bean.viewAction}" />
   </f:metadata>
   

   @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 <f:attribute> inside <f:viewParam> to "pass" parameters to the converter.

   <f:viewParam name="id" value="#{bean.id}" converter="idConverter">
       <f:attribute name="redirect" value="some.xhtml" />
   </f:viewParam>
   

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

   ---

3. Create a custom taghandler which does basically the same as <f:event listener> but without the need for an additional backing bean method.

   <html ... xmlns:my="http://example.com/ui">
   
   <f:metadata>
       <f:viewParam name="id" value="#{bean.id}" maxlength="20" />
       <my:viewParamValidationFailed redirect="some.xhtml" />
       <f:viewAction action="#{bean.viewAction}" />
   </f:metadata>
   

   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

   <?xml version="1.0" encoding="UTF-8"?>
   <facelet-taglib
       xmlns="http://java.sun.com/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facelettaglibrary_2_0.xsd"
       version="2.0"
   >
       <namespace>http://example.com/ui</namespace>
   
       <tag>
           <tag-name>viewParamValidationFailed</tag-name>
           <handler-class>com.example.taghandler.ViewParamValidationFailed</handler-class>
       </tag>  
   </facelet-taglib>
   

   /WEB-INF/web.xml

   <context-param>
       <param-name>javax.faces.FACELETS_LIBRARIES</param-name>
       <param-value>/WEB-INF/my.taglib.xml</param-value>
   </context-param>
   

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

Answer 2

Why not simply validate id yourself?

@ManagedBean
@ViewScoped
public final class TestManagedBean implements Serializable
{
    private String id;     //Getter and setter.
    private Long validId;  //Getter and setter.

    public void viewAction() {
        try {
            validId = Long.parseLong(id);
        } catch (NumberFormatException ex) {
            FacesContext facesContext = FacesContext.getCurrentInstance();
            String outcome = "redirect.xhtml";
            facesContext.getApplication().getNavigationHandler().handleNavigation(facesContext, null, outcome);
        }
    }
}