jquery ajax如何上传文件

function doUpload() {
var formData = new FormData($( "#importForm" )[0]);
$.ajax({
url:"${path}/codes/uploadExcl.do",
type: 'POST',
data: formData,
async: false,
cache: false,
contentType: false,
processData: false,
success: function (returndata) {
var flag = eval(returndata);
//var flag = returndata;
if(flag!="SUCCESS"){
alert(flag);
} else{
alert("导入成功！");
window.location.href="${path}/pc/list.do";
}
},
error: function (returndata) {
alert("导入失败:"+JSON.stringify(returndata));
}
});
}

<form id="importForm"  method="post" enctype="multipart/form-data"
class="form-search" style="padding-left:20px;text-align:center;"><br/>
<input id="uploadFile" name="file" type="file" style="width:330px" accept="application/vnd.ms-excel"/><br/><br/>　　
<input id="btnImportSubmit" class="btn btn-primary" type="button" value="导    入   " onclick="doUpload()"/>
</form>