using ExternalContext.dispatch in JSF error handler causes corrupt page rendering

Question

Simplified, my error handler looks like this: ``` @Override public void handle() throws FacesException { Iterator unhandledExceptionQueuedEvents = getUnhandledExceptionQueuedEvents().iterator(); FacesContext context = FacesContext.getCurrentInstance(); if (unhandledExceptionQueuedEvents.hasNext()) { Throwable exception = unhandledExceptionQueuedEvents.next().getContext().getException(); unhandledExceptionQueuedEvents.remove(); context.getExternalContext().dispatch("/error.jsf"); } while (unhandledExceptionQueuedEvents.hasNext()) { unhandledExceptionQueuedEvents.next(); unhandledExceptionQueuedEvents.remove(); } } ``` simplified template.xhtml ```

``` error.xhtml ``` ERROR

Accepted Answer

You should not use `ExternalContext#dispatch()` to render a JSF view. It should only be used to forward to a non-JSF resource. You should instead set the desired JSF view by `FacesContext#setViewRoot()` and let JSF render it.

```
ViewHandler viewHandler = context.getApplication().getViewHandler();
UIViewRoot viewRoot = viewHandler.createView(context, viewId);
context.setViewRoot(viewRoot);
context.renderResponse();
```

Or, if you're currently already sitting in the render response, then it's too late to let JSF re-render it. You'd need to build and render the new view manually. In that case, replace the last line by:

```
ViewDeclarationLanguage vdl = viewHandler.getViewDeclarationLanguage(context, viewId);
vdl.buildView(context, viewRoot);
context.getApplication().publishEvent(context, PreRenderViewEvent.class, viewRoot);
vdl.renderView(context, viewRoot);
context.responseComplete();
```

Note that this is in turn too late if the response is already committed. You may want to check that beforehand as well.

You may find the source code of the OmniFaces `FullAjaxExceptionHandler` helpful to get some insight.

using ExternalContext.dispatch in JSF error handler causes corrupt page rendering

Solution

Problem