304响应， CORS问题: 没有 Access-Control-Allow-Origin 这个头信息时，以前次返回的200请求为准。
示例：可能已被删除
http://7af3zm.com1.z0.glb.clouddn.com/ajax_304_cors.html
附上源码：
html
<!doctype html>
<html>
<head>
<meta charset="UTF-8">
</head>
<body>
<script type="text/javascript">
// var _ajax_34re = false;
function getAjax () {
var _ajax_34re = false;
if (_ajax_34re) {
return _ajax_34re;
}
try {
_ajax_34re = new XMLHttpRequest();
} catch (trymicrosoft) {
try {
_ajax_34re = new ActiveXObject("Msxml2.XMLHTTP");
} catch (othermicrosoft) {
try {
_ajax_34re = new ActiveXObject("Microsoft.XMLHTTP");
} catch (failed) {
_ajax_34re = false;
}
}
}
return _ajax_34re;
}
function load(url) {
request = getAjax ();
request.open("GET", url);
request.onreadystatechange = updatePage;
request.send(null);
}
function updatePage() {
if (request.readyState == 4)
if (request.status == 200)
alert("Server is done!" + request.responseText);
else if (request.status == 404)
alert("Request URL does not exist");
else
alert("Error: status code is " + request.status);
}
</script>
<pre>
access: 200、304响应都有 Access-Control-Allow-Origin:*;
access-non: 200、304响应都 没 有 Access-Control-Allow-Origin;
access-200: 200响应都有 Access-Control-Allow-Origin:*, 304响应 没 有 Access-Control-Allow-Origin;
</pre>
<input type="button" onclick='load("http://73a8eb41cb.a.passageway.io/access")' value="access" />
<input type="button" onclick='load("http://73a8eb41cb.a.passageway.io/access-non")' value="access-non" />
<input type="button" onclick='load("http://73a8eb41cb.a.passageway.io/access-200")' value="access-200" />
</body>
</html>
clojure
(ns base-web.handler
(:require [compojure.core :refer :all]
[compojure.route :as route]
[ring.middleware.defaults :refer [wrap-defaults site-defaults]]
[clojure.pprint :as log]))
(def my-route
(-> site-defaults
(assoc-in [:security :anti-forgery] false)
(assoc-in [:params] false)
))
(defn print-req [req]
(println )
(log/pprint my-route)
(log/pprint req)
(log/pprint (slurp (:body req)))
(println "done"))
(defn access-200 [req]
(let [etag "e-access-200"]
(if (not= etag (get-in req [:headers "if-none-match"]))
(do (println "200")
{:status 200,
:headers {"Content-Type" "application/json", "Access-Control-Allow-Origin" "*", "ETag" etag}
:body "{\"success\":true, \"frame\": \"ring\"}"})
(do (println "304")
{:status 304,
:headers {"Content-Type" "application/json", "ETag" etag}}))))
(defn access-non [req]
(let [etag "e-access-non"]
(if (not= etag (get-in req [:headers "if-none-match"]))
(do (println "200")
{:status 200,
:headers {"Content-Type" "application/json", "ETag" etag}
:body "{\"success\":true, \"frame\": \"ring\"}"})
(do (println "304")
{:status 304,
:headers {"Content-Type" "application/json", "ETag" etag}}))))
(defn access [req]
(let [etag "e-access"]
(if (not= etag (get-in req [:headers "if-none-match"]))
(do (println "200")
{:status 200,
:headers {"Content-Type" "application/json", "Access-Control-Allow-Origin" "*", "ETag" etag}
:body "{\"success\":true, \"frame\": \"ring\"}"})
(do (println "304")
{:status 304,
:headers {"Content-Type" "application/json", "ETag" etag}}))))
(defroutes app-routes
(GET "/access-200" req (access-200 req) )
(GET "/access-non" req (access-non req) )
(GET "/access" req (access req) )
(ANY "*" req
(print-req req)
"{\"success\":true, \"frame\": \"compojure\"}")
(route/not-found "Not Found"))
(def app
(wrap-defaults app-routes my-route))
;; lein ring server [<port>]