从netty源码里拿到的关于http错误码，自己学习下

     public static HttpResponseStatus valueOf(int code) {
         switch (code) {
         case 100:
             return CONTINUE;
         case 101:
             return SWITCHING_PROTOCOLS;
         case 102:
             return PROCESSING;
         case 200:
             return OK;
         case 201:
             return CREATED;
         case 202:
             return ACCEPTED;
         case 203:
             return NON_AUTHORITATIVE_INFORMATION;
         case 204:
             return NO_CONTENT;
         case 205:
             return RESET_CONTENT;
         case 206:
             return PARTIAL_CONTENT;
         case 207:
             return MULTI_STATUS;
         case 300:
             return MULTIPLE_CHOICES;
         case 301:
             return MOVED_PERMANENTLY;
         case 302:
             return FOUND;
         case 303:
             return SEE_OTHER;
         case 304:
             return NOT_MODIFIED;
         case 305:
             return USE_PROXY;
         case 307:
             return TEMPORARY_REDIRECT;
         case 400:
             return BAD_REQUEST;
         case 401:
             return UNAUTHORIZED;
         case 402:
             return PAYMENT_REQUIRED;
         case 403:
             return FORBIDDEN;
         case 404:
             return NOT_FOUND;
         case 405:
             return METHOD_NOT_ALLOWED;
         case 406:
             return NOT_ACCEPTABLE;
         case 407:
             return PROXY_AUTHENTICATION_REQUIRED;
         case 408:
             return REQUEST_TIMEOUT;
         case 409:
             return CONFLICT;
         case 410:
             return GONE;
         case 411:
             return LENGTH_REQUIRED;
         case 412:
             return PRECONDITION_FAILED;
         case 413:
             return REQUEST_ENTITY_TOO_LARGE;
         case 414:
             return REQUEST_URI_TOO_LONG;
         case 415:
             return UNSUPPORTED_MEDIA_TYPE;
         case 416:
             return REQUESTED_RANGE_NOT_SATISFIABLE;
         case 417:
             return EXPECTATION_FAILED;
         case 422:
             return UNPROCESSABLE_ENTITY;
         case 423:
             return LOCKED;
         case 424:
             return FAILED_DEPENDENCY;
         case 425:
             return UNORDERED_COLLECTION;
         case 426:
             return UPGRADE_REQUIRED;
         case 428:
             return PRECONDITION_REQUIRED;
         case 429:
             return TOO_MANY_REQUESTS;
         case 431:
             return REQUEST_HEADER_FIELDS_TOO_LARGE;
         case 500:
             return INTERNAL_SERVER_ERROR;
         case 501:
             return NOT_IMPLEMENTED;
         case 502:
             return BAD_GATEWAY;
         case 503:
             return SERVICE_UNAVAILABLE;
         case 504:
             return GATEWAY_TIMEOUT;
         case 505:
             return HTTP_VERSION_NOT_SUPPORTED;
         case 506:
             return VARIANT_ALSO_NEGOTIATES;
         case 507:
             return INSUFFICIENT_STORAGE;
         case 510:
             return NOT_EXTENDED;
         case 511:
             return NETWORK_AUTHENTICATION_REQUIRED;
         }

         final String reasonPhrase;

         if (code < 100) {
             reasonPhrase = "Unknown Status";
         } else if (code < 200) {
             reasonPhrase = "Informational";
         } else if (code < 300) {
             reasonPhrase = "Successful";
         } else if (code < 400) {
             reasonPhrase = "Redirection";
         } else if (code < 500) {
             reasonPhrase = "Client Error";
         } else if (code < 600) {
             reasonPhrase = "Server Error";
         } else {
             reasonPhrase = "Unknown Status";
         }

         return new HttpResponseStatus(code, reasonPhrase + " (" + code + ')');
     }