Ajax请求(415 Unsupported Media Type)

 Unsupported media type-415(不支持的媒体类型)

该错误类型是后台接收参数为json类型的，然而ajax提交的类型不对，如下：

异常代码：

$.ajax({
            url: api + "/sendMessage",
            type: "post",
            dataType : "json",
            cache: false,
            data: {
                mobile: base.encode(phone),
                message: base.encode(sms)
            },
            success: function(data) {
                if(data.ret == "0") {
                    layer.msg('短信已发到您手机', {icon: 1}); 
                } else {
                    countdown=0;
                    layer.msg('发送失败，请稍后重试', {icon: 2}); 
                }
            },
            error: function(data) {
                countdown=0;
                layer.msg('发送异常，请稍后重试', {icon: 2}); 
            }
        });

正确代码：

$.ajax({
            url: api + "/sendMessage",
            type: "post",
            dataType : "json",
            contentType: 'application/json',
            cache: false,
            data: JSON.stringify({
                mobile: base.encode(phone),
                message: base.encode(sms)
            }),
            success: function(data) {
                if(data.ret == "0") {
                    layer.msg('短信已发到您手机', {icon: 1}); 
                } else {
                    countdown=0;
                    layer.msg('发送失败，请稍后重试', {icon: 2}); 
                }
            },
            error: function(data) {
                countdown=0;
                layer.msg('发送异常，请稍后重试', {icon: 2}); 
            }
        });