后台通过读取流的形式，实现下载功能

jsp前台：jsp代码内潜入隐藏的form

                 <div class="accordion">
				<map name="FPMap0">
					<area  href="/go.html?url=#" onclick="downloads();"  shape="rect" coords="7, 198, 181, 250">
				</map>
				<ul style="display: inline-block;">
					<img src="${ctx}/images/lc.gif"  usemap="#FPMap0"/>
				</ul>
			</div>
			<span style="color:#ff0000;"><form id="uploadForm" action="${ctx}/upload/downloadFile" method="post">
				<input type="hidden" name="fileName" id="fileName" />
			</form></span>                 <di