通过Ajax上载文件实际上是不可能的。您仍然可以使用隐藏的iframe在后台上传文件，并评估响应（位于iframe内）或在上传完成后触发另一个ajax调用。

<g:form name="upload-form" action="upload" method="post" enctype="multipart/form-data" target="hidden-upload-frame">
    File: <input type="file" name="myFile" />
    <button type="submit">Upload</button>
</g:form>

<iframe id="hidden-upload-frame" name="hidden-upload-frame" style="display: none" onload="onUploadComplete">
</iframe>

<script type="text/javascript">
    function onUploadComplete(e) {
        // Handle upload complete
        alert("upload complete");
        // Evaluate iframe content or fire another ajax call to get the details for the previously uploaded file
    }
</script>

另一种选择是使用基于Flash的上传机制（例如swfupload）代替iframe。