怎么解决ASP.NET开发web应用遇到的javascript跨域请求问题

.ashx代码using System; using System.Collections.Generic; using System.Linq; using System.Web;  namespace KB.DSN.Web.API.Tokens {     /// <summary>     /// Summary description for Get     /// </summary>     public class Get : IHttpHandler     {           public void Proce***equest(HttpContext context)         {             setresponsecontext(context);             var token = KB.DSN.BusinessAccess.UniqueCommunicationCode.GenerateUniqueCommunicationCode();              var outputobject = new             {                 Head = new Models.KBJsonHeadResponse(),                 Body = new { Token = token }             };              var outputjsonstring = Newtonsoft.Json.JsonConvert.SerializeObject(outputobject);                           context.Response.Write(context.Request.QueryString["callback"]+"("+outputjsonstring+")");          }          private void setresponsecontext(HttpContext context)         {                         context.Response.ContentEncoding = System.Text.Encoding.UTF8;             context.Response.ContentType = "application/json";         }          public bool IsReusable         {             get             {                 return false;             }         }     } }AI代码助手复制代码html页面function getToken_jsonp(){         $.ajax({        url: "http://192.168.0.111/api/tokens/get.ashx",           type: "get",      dataType: "jsonp",     jsonp: "callback",     async: false,                contentType: "application/json",           success: function(data){       //alert("getToken success");             $("#token").text($.toJSON(data));             //console.log(data);                  },     error:function(){         alert("getToken fail");     }         });        }AI代码助手复制代码

<system.webServer>    <httpProtocol>     <customHeaders>       <add name="Access-Control-Allow-Methods" value="OPTIONS,POST,GET"/>       <add name="Access-Control-Allow-Headers" value="x-requested-with"/>       <add name="Access-Control-Allow-Origin" value="*" />     </customHeaders>   </httpProtocol> </system.webServer>

function addContact() {            var contact = new Object();            contact.FirstName = $("#firstName").attr("value");            contact.LastName = $("#lastName").attr("value");            contact.PhoneNo = $("#phoneNo").attr("value");            contact.EmailAddress = $("#emailAddress").attr("value");            $.ajax({                url: "http://localhost:10401/api/contacts/AddContact.ashx",                type: "POST",                 dataType: "json",                data: $.toJSON(contact),                  success: function () { loadAllContacts(); }            });        }

 这种方式不能设置contentType: "application/json"，否则会提示"Request header field Content-Type is not allowed by Access-Control-Allow-Headers."去掉ajax中的contentType设置就可以了！  想要设置contentType也可以，需要将web.config文件中的<add name="Access-Control-Allow-Headers" value="x-requested-with"/> 修改为<add name="Access-Control-Allow-Headers" value="x-requested-with,content-type"/>

/// <summary>    /// Summary description for FindContact    /// </summary>    public class FindContact : IHttpHandler    {        public void Proce***equest(HttpContext context)        {            context.Response.ContentEncoding = Encoding.UTF8;            context.Response.ContentType = "application/json";            var stream = context.Request.InputStream;            var reader = new StreamReader(stream);            var input=reader.ReadToEnd();            var o = Newtonsoft.Json.JsonConvert.DeserializeObject<Models.Contact>(input);            var list = new List<Models.Contact>();            list.Add(o);            list.Add(o);            context.Response.Write(Newtonsoft.Json.JsonConvert .SerializeObject ( list ));        }        public bool IsReusable        {            get            {                return false;            }        }    } 2.在请求中设置HttpHeader针对单个请求。FindContact.ashx/// <summary>    /// Summary description for FindContact    /// </summary>    public class FindContact : IHttpHandler    {         public void Proce***equest(HttpContext context)        {            context.Response.ContentEncoding = Encoding.UTF8;            context.Response.ContentType = "application/json";             var stream = context.Request.InputStream;            var reader = new StreamReader(stream);            var input=reader.ReadToEnd();             var o = Newtonsoft.Json.JsonConvert.DeserializeObject<Models.Contact>(input);            var list = new List<Models.Contact>();            list.Add(o);            list.Add(o);             #region 支持跨域请求            context.Response.ClearHeaders();            string origin = context.Request.Headers["Origin"];            context.Response.AppendHeader("Access-Control-Allow-Origin",                string.IsNullOrEmpty(origin) ? "*" : origin);            string requestHeaders = context.Request.Headers["Access-Control-Request-Headers"];            context.Response.AppendHeader("Access-Control-Allow-Headers",                string.IsNullOrEmpty(requestHeaders) ? "*" : requestHeaders);            context.Response.AppendHeader("Access-Control-Allow-Methods", "POST, OPTIONS");            #endregion             context.Response.Write(Newtonsoft.Json.JsonConvert .SerializeObject ( list ));        }         public bool IsReusable        {            get            {                return false;            }        }    }AI代码助手复制代码html pagefunction addContact() {            var contact = new Object();            contact.FirstName = $("#firstName").attr("value");            contact.LastName = $("#lastName").attr("value");            contact.PhoneNo = $("#phoneNo").attr("value");            contact.EmailAddress = $("#emailAddress").attr("value");            $.ajax({                url: "http://localhost:10401/api/contacts/AddContact.ashx",                type: "POST",                 dataType: "json",                data: $.toJSON(contact),                  success: function () { loadAllContacts(); }            });        }AI代码助手复制代码AI代码助手复制代码3.使用代理假设你有两个web应用：一个应用放html页面，给用户提供界面；一个应用放服务，使用.ASHX处理请求。你在html应用中使用ajax请求ashx应用的接口，就是ajax跨域请求。你可以在html应用中写一些后台代码，在代码中向ashx应用提交数据。然后你的html应用的页面中将收集到的数据发送到html应用的后台代码中，由后台代码发送数据到ashx应用，这就不是ajax跨域请求了。在html应用中的后台代码就被叫做“代理”，代理html应用到ashx应用的请求。