protected SparkApplication[] getApplications(final FilterConfig filterConfig) throws ServletException {

        String applications = filterConfig.getInitParameter(APPLICATION_CLASS_PARAM);
        SparkApplication[] solvedApplications = null;

        if (StringUtils.isNotBlank(applications)) {
            final String[] sparkApplications = applications.split(",");

            if (sparkApplications != null && sparkApplications.length > 0) {
                solvedApplications = new SparkApplication[sparkApplications.length];

                for (int index = 0; index < sparkApplications.length; index++) {
                    solvedApplications[index] = getApplication(sparkApplications[index].trim());
                }
            } else {
                throw new ServletException("There are no Spark applications configured in the filter.");
            }
        }

        return solvedApplications;
    }
Returns the instances of {@link SparkApplication} which on which {@link SparkApplication#init() init()} will be called.
Default implementation looks up the class names in the filterConfig using the key {@value #APPLICATION_CLASS_PARAM}.
Subclasses can override this method to use different techniques to obtain an instance (i.e. dependency injection).

@param filterConfig the filter configuration for retrieving parameters passed to this filter.
@return the spark applications containing the configuration.
@throws ServletException if anything went wrong.
src/main/java/spark/servlet/SparkFilter.java