出现错误无法加载资源：请求的资源上不存在“ Access-Control-Allow-Origin”标头

Question

I am getting the following error:
Failed to load resource: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'domain' is therefore not allowed access. domain/api/login XMLHttpRequest cannot load api/login. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'domain' is therefore not allowed access.

<script type="text/javascript">


function ajax_trial() {

    var user_name="admin@abc.com";
    var passcode = "1233";
    var client_app_code = "1";
    var ip_address = "someIP";




    var json_string = '{"user_name" : "'+user_name+'","passcode":"'+passcode+'","client_app_code":"'+client_app_code+'","ip_address":"'+ip_address+'"}';

        alert(json_string);
    $.ajax({

        'accept': 'application/json',
        'contentType': 'application/json',
         type: "POST",
        dataType: "json",
        'data': json_string,
        cache: true,
        crossDomain: true,
        url: "/api/login",
        success: function(data) {
            alert("data "+data);
        },
        error: function(xhr, status, error) {
            alert(xhr.responseText);
        }
    });

}

i user a rest client and this is code i get when i send the json {"user_name":"admin@domain.com","passcode":"1233","client_app_code":"1","ip_address":"1323"}

Request headers 
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko)
Chrome/31.0.1650.63 Safari/537.36
Origin: chrome-extension://hgmloofddffdnphfgcellkdfbfbjeloo
Content-Type: application/json
Accept: */*
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8,it;q=0.6
Response headers 
Server: Apache-Coyote/1.1
sessionId: 94c16db2-6bb8-11e3-a4e7-7845c4b4
Access-Control-Allow-Origin: *
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Type: application/json
Transfer-Encoding: chunked
Date: Mon, 23 Dec 2013 09:57:06 GMT 

Answer 1

I think you are sending an AJAX request to a different domain. That is, you are sending a request from your "localhost" to "something.com". This is limited by the browsers due to Same Origin Policy .

The web browser is blocking it as it usually allows request in the same origin for security reason.

You'll need to do something different to do a cross-domain XHR. JSON-P is one way of achieving it.

Answer 2

在克服开发过程中，您可以在浏览器中使用名为CORS的插件。