同时上传文件

I want to upload files at the same time. When I select 2 files and submit them, req.getParts().size() is 1, however I expected it to be 2. How do I get two parts?

<input type="file" name="file" multiple>
<input type="button" onclick="upload()">

function upload() {

var formData = new FormData();
fd.append('file',  jQuery("input[name=file]").get(0).files);

jQuery.ajax({
    url : url,
    type: "POST",
    dataType : "json",
    contentType : false,
    processData : false,
    data : formData,

    success : function() {...}
});

}