public class FlashMapFilter extends OncePerRequestFilter {
@Override
@SuppressWarnings("unchecked")
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
HttpSession session = request.getSession(false);
if (session != null) {
Map<String, ?> flash = (Map<String, ?>) session.getAttribute(FlashMap.FLASH_MAP_ATTRIBUTE);
if (flash != null) {
for (Map.Entry<String, ?> entry : flash.entrySet()) {
Object currentValue = request.getAttribute(entry.getKey());
if (currentValue == null) {
request.setAttribute(entry.getKey(), entry.getValue());
}
}
session.removeAttribute(FlashMap.FLASH_MAP_ATTRIBUTE);
}
}
filterChain.doFilter(request, response);
}
}
而不是每個請求顯示一次Flash消息,這會顯示一條消息,消息之前的兩個完整請求的持續時間。這是爲什麼?爲什麼我的FlashMapFilter顯示兩個請求,即使它擴展了OncePerRequestFilter?