I suggest this solution below.
public void doFilter(ServletRequest req, ServletResponse res,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
final String val = request.getHeader(FOO_TOKEN)
if (val == null || !val.equals("FOO")) {
((HttpServletResponse) response).sendError(HttpServletResponse.SC_UNAUTHORIZED, "The token is not valid.");
} else {
chain.doFilter(req, res);
}
}