ExternalContext#redirect() with includeViewParams=true - jsf

Question

Using a list of currencies in the form of strings as follows.
<p:selectOneMenu id="currency"
value="#{currencyRateBean.currency}"
onchange="changeCurrency([{name: 'currency', value: this.value}]);">
<f:selectItems var="row"
value="#{currencyBean.currencies}"
itemLabel="#{row}"
itemValue="#{row}"/>
</p:selectOneMenu>
Along a <p:remoteCommand>.
<p:remoteCommand ignoreAutoUpdate="true"
name="changeCurrency"
partialSubmit="true"
process="#this"
update="#none"
action="#{currency.currencyAction}"/>
The managed bean setting a currency value being passed through the above <p:remoteCommand> as a parameter to a JavaScript function.
#Named
#RequestScoped
public class Currency {
#Inject
#HttpParam
private String currency;
#Inject
private CurrencyRateBean currencyRateBean;
public Currency() {}
public String currencyAction() throws MalformedURLException, IOException {
try (Scanner scanner = new Scanner(new URL("http://www.exchangerate-api.com/INR/" + currency + "/1?k=FQRxs-xT2tk-NExQj").openConnection().getInputStream(), "UTF-8");) {
currencyRateBean.setCurrencyRate(scanner.nextBigDecimal());
currencyRateBean.setCurrency(currency);
} catch (UnknownHostException | ConnectException e) {}
return FacesContext.getCurrentInstance().getViewRoot().getViewId() + "?faces-redirect=true&includeViewParams=true";
}
}
The supplied currency value is then set to another session scoped managed bean CurrencyRateBean from within the action method currencyAction() above which finally makes a redirect based on the current value of viewId along with includeViewParams=true which is important.
Now, the story changes, when #{currencyRateBean.currencies} has been changed to have a list of composite objects which has been a list of Strings so far.
The following scenario will not work with includeViewParams=true which is significant.
<p:selectOneMenu value="#{currencyRateBean.currencyHolder}">
<f:selectItems var="row" value="#{currencyBean.currencies}"
itemLabel="#{row.currency}"
itemValue="#{row}"/>
<p:ajax event="change"
listener="#{currency.currencyAction}"
partialSubmit="true"
process="#this"
update="#none"/>
</p:selectOneMenu>
public void currencyAction() throws IOException {
// ...
FacesContext facesContext = FacesContext.getCurrentInstance();
String viewId = facesContext.getViewRoot().getViewId();
ExternalContext externalContext = facesContext.getExternalContext();
externalContext.redirect(externalContext.getRequestContextPath() + viewId + "?includeViewParams=true");
}
includeViewParams=true has been added for decoration only. It is not going to work.
Since listener in <p:ajax> is incapable of making a redirect based on a navigation case outcome as done by action of <p|h:commandXxx>, ExternalContext#redirect() has to be used anyway.
<p:remoteCommand> can be used on complete of <p:ajax> but this will involve two round trips to the server unnecessarily, first to set the currency value to the associated managed bean and then to make a redirect.
How to make a redirect with includeViewParams=true in the example given?

Answer 1

Like faces-redirect=true, includeViewParams=true works only in navigation outcomes, not in "plain" URLs which you pass to ExternalContext#redirect().
Use NavigationHandler#handleNavigation().
FacesContext context = FacesContext.getCurrentInstance();
String outcome = viewId + "?includeViewParams=true";
context.getApplication().getNavigationHandler().handleNavigation(context, null, outcome);
Or, with OmniFaces.
Faces.navigate(viewId + "?includeViewParams=true");
A dubious alternative is to collect all view parameters yourself and convert them to query string so you can use ExternalContext#redirect() anyway. This is easier with OmniFaces.
Faces.redirect(viewId + "?" + Servlets.toQueryString(Faces.getViewParameterMap()));