ajax中的contentType有多种类型，默认是contentType=application/x-www-form-urlencoded;charset=utf-8;，如果设置contentType=application/json;charset=utf-8;那就会发生在后台无法通过context.Request.Form[]获取参数的情况，下面我就post、get两种方式进行梳理。

post传值

前台代码，data是json字符串：

function PostSendParams() {
    $.ajax({
        type: "post",url: "Handler1.ashx",contentType: "application/json;charset=utf-8;",data: "{ \"contentType\": \"application/json\",\"param2\": \"18\" }",dataType: "json",success:function(data) {
            alert("data=" + data);
        },error:function(error) {
            alert("error=" + error);
        }
    });
}

后台取值：

public void ProcessRequest(HttpContext context)
{
    try
    {
        #region Form取值(不行)
        //string contentType = context.Request.Form["contentType"].ToString();
        //string param2 = context.Request.Form["param2"].ToString();
        #endregion

        #region InputStream取值（可以）
        Stream stream = context.Request.InputStream;
        byte[] bytes = new byte[stream.Length];
        stream.Read(bytes,0,bytes.Length);
        string parameters = Encoding.Default.GetString(bytes);
        JObject jObject = (JObject)JsonConvert.DeserializeObject(parameters);
        string contentType = jObject["contentType"].ToString();
        string param2 = jObject["param2"].ToString(); 
        #endregion 
    }
    catch (Exception ex)
    {
        context.Response.Write("error");
    }
}

前台代码，data是json对象：

function PostSendParams() {
    $.ajax({
        type: "post",data: { contentType: "application/json",param2: 18 },error:function(error) {
            alert("error=" + error);
        }
    });
}

后台取值：

public void ProcessRequest(HttpContext context)
{
    try
    {
        #region Form取值(不行)
        //string contentType = context.Request.Form["contentType"].ToString();
        //string param2 = context.Request.Form["param2"].ToString();
        #endregion

        #region InputStream取值（不行）
        Stream stream = context.Request.InputStream;
        byte[] bytes = new byte[stream.Length];
        stream.Read(bytes,bytes.Length);
        string parameters = Encoding.Default.GetString(bytes);
        JObject jObject = (JObject)JsonConvert.DeserializeObject(parameters);
        string contentType = jObject["contentType"].ToString();
        string param2 = jObject["param2"].ToString(); 
        #endregion 
    }
    catch (Exception ex)
    {
        context.Response.Write("error");
    }
}

get传值

前台代码，data是json字符串：

function GetSendParams() {
    $.ajax({
        type: "get",success: function (data) {
            alert("data=" + data);
        },error: function (error) {
            alert("error=" + error);
        }
    });
}

后台取值：

public void ProcessRequest(HttpContext context)
{
    try
    {
        #region QueryString取值（不行）
        //string contentType = context.Request.QueryString["contentType"].ToString();
        //string param2 = context.Request.QueryString["param2"].ToString();
        #endregion

        #region InputStream取值（不行）
        Stream stream = context.Request.InputStream;
        byte[] bytes = new byte[stream.Length];
        stream.Read(bytes,bytes.Length);
        string parameters = Encoding.Default.GetString(bytes);
        JObject jObject = (JObject)JsonConvert.DeserializeObject(parameters);
        string contentType = jObject["contentType"].ToString();
        string param2 = jObject["param2"].ToString();
        #endregion
    }
    catch (Exception ex)
    {
        context.Response.Write("error");
    }
}

前台代码，data是json对象：

function GetSendParams() {
    $.ajax({
        type: "get",error: function (error) {
            alert("error=" + error);
        }
    });
}

后台取值：

public void ProcessRequest(HttpContext context)
{
    try
    {
        #region QueryString取值（可以）
        string contentType = context.Request.QueryString["contentType"].ToString();
        string param2 = context.Request.QueryString["param2"].ToString();
        #endregion

        #region InputStream取值（不行）
        //Stream stream = context.Request.InputStream;
        //byte[] bytes = new byte[stream.Length];
        //stream.Read(bytes,bytes.Length);
        //string parameters = Encoding.Default.GetString(bytes);
        //JObject jObject = (JObject)JsonConvert.DeserializeObject(parameters);
        //string contentType = jObject["contentType"].ToString();
        //string param2 = jObject["param2"].ToString();
        #endregion
    }
    catch (Exception ex)
    {
        context.Response.Write("error");
    }
}

总结

当contentType=application/json;charset=utf-8;时，post传值只有在data是json字符串后台用InputStream进行解析，才能获取参数； 当contentType=application/json;charset=utf-8;时，get传值只有在data是json对象后台用QueryString进行解析，才能获取参数。