This method is implemented based on iframe. The requirement is that form form submission has input tag uploaded by file, so ajax cannot be used to submit
first:
The code copy is as follows:
<form id="form0" action="${pageContext.request.contextPath}/news/baikeAdd.form" enctype="multipart/form-data" method="POST" target="hidden_frame">
... ...
</form>
<iframe name='hidden_frame' id="hidden_frame" style='display:none'></iframe>
The attribute values in the red character must be the same