Filter를 상속한 OncePerRequestFilter

JWT filter 로 등록할때, OncePerRequestFilter를 상속하였는데,

public class JwtFilter extends OncePerRequestFilter {}

이 친구 들여다보면, DispatcherType 이 Error 인 경우 뭔짓거리를 하고 있음.

public abstract class OncePerRequestFilter extends GenericFilterBean {

	/**
	 * Suffix that gets appended to the filter name for the
	 * "already filtered" request attribute.
	 * @see #getAlreadyFilteredAttributeName
	 */
	public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";


	/**
	 * This {@code doFilter} implementation stores a request attribute for
	 * "already filtered", proceeding without filtering again if the
	 * attribute is already there.
	 * @see #getAlreadyFilteredAttributeName
	 * @see #shouldNotFilter
	 * @see #doFilterInternal
	 */
	@Override
	public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		if (!((request instanceof HttpServletRequest httpRequest) && (response instanceof HttpServletResponse httpResponse))) {
			throw new ServletException("OncePerRequestFilter only supports HTTP requests");
		}

		String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
		boolean hasAlreadyFilteredAttribute = request.getAttribute(alreadyFilteredAttributeName) != null;

		if (skipDispatch(httpRequest) || shouldNotFilter(httpRequest)) {
			// Proceed without invoking this filter...
			filterChain.doFilter(request, response);
		}
		else if (hasAlreadyFilteredAttribute) {
			if (DispatcherType.ERROR.equals(request.getDispatcherType())) {
				doFilterNestedErrorDispatch(httpRequest, httpResponse, filterChain);
				return;
			}

			// Proceed without invoking this filter...
			filterChain.doFilter(request, response);
		}
		else {
			// Do invoke this filter...
			request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);
			try {
				doFilterInternal(httpRequest, httpResponse, filterChain);
			}
			finally {
				// Remove the "already filtered" request attribute for this request.
				request.removeAttribute(alreadyFilteredAttributeName);
			}
		}
	}

즉, DispatcherType 이 Error인 경우에, WAS에서 오류 처리에 의한 호출인 경우에는 필요없는 필터나, 인터셉터를 거치게 된다.

이를 방지하기 위한 목적으로 OncePerRequestFilter가 사용된다.
JwtFilter 인증이 한번만 되면 OK이므로, 프로젝트에서 OncePerRequestFilter를 적용시켰다.