angularjs中$http异步上传Excel文件方法

<form id="fileForm" enctype="multipart/form-data">
 <button id="import_asset" type="button" ng-click="import_asset()">上传文件</button>
 <input id="file_asset" type="file" style="display: none;"/>
</form>

$scope.import_asset = function () {
 $("#file_asset").click();
};
$("#file_asset").on("change", function(){
 var formData = new FormData();
 var file = document.getElementById("file_asset").files[0];
 if(file.name){
  var fileName = file.name.substring(file.name.lastIndexOf(".") + 1);
  if(fileName =="xlsx" || fileName =="xls"){
   formData.append('file', file);
   $http({
    method:"post",
    url:monService.projectName + "/so/assetmanage/upload",
    data:formData,
    headers : {
     'Content-Type' : undefined
    },
    transformRequest : angular.identity
   }).then(function (response) {
    if(response.status == 200){
     alert("文件上传成功！！！");
    }else{
     alert("文件上传失败！！！");
    }
   });
  }else{
   alert("文件格式不正确，请上传以.xlsx，.xls 为后缀名的文件。");
   $("#file_asset").val("");
  }
 }
});