jsonp请求返回前面带有个null

 正确写法：

$.ajax({
    type: "get",
    url: '<%=APP_URL_ZZGRID%>/zzgl/map/data/situation/getPlayRtspJsonp.json',
    dataType: "jsonp",
    jsonp: "jsoncallback",
    data: {
        monitorId: monitorId
    },
    success: function (data) {
        if (data.rtspUrl != '' && data.rtspUrl != undefined ) {
            var rtsp = data.rtspUrl.replace(/?/g, '%3F').replace(/&/g, '%26').replace(/=/g, '%3D');
            var url="<%=skyDomain%>/shequ/video/index.jhtml?streamAddr="+rtsp;
            $('#monitor_1').html('<iframe  src="'+url+'" allowfullscreen="true" allowtransparency="true" webkitallowfullscreen="true" width="100%" height="100%" scrolling="no"></iframe>');
        } else {
            $.messager.alert('错误','获取播放链接失败！','error');
        }
    },
    error:function(data){
        $.messager.alert('错误','获取rtsp异常！','error');
    }
错误写法：

$.ajax({
    type: "POST",
    url: '<%=APP_URL_ZZGRID%>/zzgl/map/data/situation/getPlayRtspJsonp.json',
    dataType: "jsonp",
    data: {
        monitorId: monitorId
    },
    success: function (data) {
        if (data.rtspUrl != '' && data.rtspUrl != undefined ) {
            var rtsp = data.rtspUrl.replace(/?/g, '%3F').replace(/&/g, '%26').replace(/=/g, '%3D');
            var url="<%=skyDomain%>/shequ/video/index.jhtml?streamAddr="+rtsp;
            $('#monitor_1').html('<iframe  src="'+url+'" allowfullscreen="true" allowtransparency="true" webkitallowfullscreen="true" width="100%" height="100%" scrolling="no"></iframe>');
        } else {
            $.messager.alert('错误','获取播放链接失败！','error');
        }
    },
    error:function(data){
        $.messager.alert('错误','获取rtsp异常！','error');
    }
});
原因：接口带有

});