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Custom Error Handling

Customizing error views related to navigation between routes.

You can customize the error views related to navigation between different routes, as described in the Router Exception Handling documentation page.

For other unhandled runtime exceptions, an ErrorHandler class can be used to let users know that something went wrong. To do so, first create a custom ErrorHandler class. Then use that class to override the default error handler.

For example, the following CustomErrorHandler class logs the error and displays a notification to the user:

public class CustomErrorHandler implements ErrorHandler {

    private static final Logger logger = LoggerFactory.getLogger(CustomErrorHandler.class);

    @Override
    public void error(ErrorEvent errorEvent) {
        logger.error("Something wrong happened", errorEvent.getThrowable());
        if(UI.getCurrent() != null) {
            UI.getCurrent().access(() -> {
                Notification.show("An internal error has occurred." +
                        "Contact support for assistance.");
            });
        }
    }
}

Next, assign the custom error handler to the current user session like this:

VaadinSession.getCurrent().setErrorHandler(new CustomErrorHandler());

To apply the custom error handler to all user sessions, you can use a SessionInitListener, which receives an event each time a new VaadinSession is initialized. See the Session and UI Listeners documentation page to learn how to create a SessionInitListener.

ErrorEvent has method getComponent() to get the handled Component, and the getElement() method to get the handled Element when the error is thrown if available.

For example, the following button click listener would have ErrorEvent getComponent() return the clicked button:

Button button = new Button("Click me", event -> {
    throw new IllegalArgumentException("No clicking");
});

Show Error Parameter Views for Non-Navigation Exceptions

In the DefaultErrorHandler, it’s possible to enable transitioning to an HasErrorParameter<T extends Exception> error view on exceptions. This is done by setting the enableErrorHandlerRedirect parameter to true. See Error Resolving for more information on the HasErrorParameter.

For a customized error handler, the same can be done by using the ErrorHandlerUtil method, handleErrorByRedirectingToErrorView like so:

public class CustomErrorHandler implements ErrorHandler {

    private static final Logger logger = LoggerFactory.getLogger(CustomErrorHandler.class);

    @Override
    public void error(ErrorEvent errorEvent) {
        boolean redirected = ErrorHandlerUtil
            .handleErrorByRedirectingToErrorView(event.getThrowable());
        if (!redirected) {
            // We did not have a matching error view, logging and showing notification.
            logger.error("Something wrong happened", errorEvent.getThrowable());
            if(UI.getCurrent() != null) {
                UI.getCurrent().access(() -> {
                    Notification.show("An internal error has occurred." +
                            "Contact support for assistance.");
                });
            }
        }
    }
}

Calling handleErrorByRedirectingToErrorView shows the error view with the exact matching exception. As a result, for AccountingException, only the exact match MyAccountingException implements HasErrorParameter<AccountingException> is accepted and rendered.

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