@Override
    public void init(FilterConfig filterConfig) throws ServletException {
        ServletFlag.runFromServlet();

        applications = getApplications(filterConfig);

        for (SparkApplication application : applications) {
            application.init();
        }

        filterPath = FilterTools.getFilterPath(filterConfig);

        matcherFilter = new MatcherFilter(ServletRoutes.get(), StaticFilesConfiguration.servletInstance, ExceptionMapper.getServletInstance(), true, false);
    }
It contains all the Spark application instances that was declared in the filter configuration. They can be one or more
class names separated by commas.
src/main/java/spark/servlet/SparkFilter.java