CorsStuff.java

private static final HashMap<String, String> corsHeaders = new HashMap<String, String>();

static {
    corsHeaders.put("Access-Control-Allow-Methods", "GET,PUT,POST,DELETE,OPTIONS");
    corsHeaders.put("Access-Control-Allow-Origin", "*");
    corsHeaders.put("Access-Control-Allow-Headers", "Content-Type,Authorization,X-Requested-With,Content-Length,Accept,Origin,");
    corsHeaders.put("Access-Control-Allow-Credentials", "true");
}

public final static void apply() {
    Filter filter = new Filter() {
        @Override
        public void handle(Request request, Response response) throws Exception {
            corsHeaders.forEach((key, value) -> {
                response.header(key, value);
            });
        }
    };
    Spark.after(filter);
}