JavaWeb项目中使用ajax上传文件

1.jsp

$("#cxsc").click(function(){
				var bankId = $("#bankId").val();
				var formdata = new FormData();
				formdata.append('logo', $('#btnFile').get(0).files[0]);
				formdata.append('bankId', bankId);
				$.ajax({
		            type: 'POST',
		            url: './uploadLogo',
		            contentType : false,
					data : formdata,
					processData : false,
		            dataType: "json",
		            success: function (data) {
		            	$("#logoImg").attr('src','${_b}/upload/banklogo/'+data.msg);
		            },
		            error : function(data) {
						alert('上传失败！');
					}
		        });

<#if formData?exists>
	          				<#if (formData.logoImg??)>
	             				<img src="${_b}/upload/banklogo/${formData.logoImg}" style="120px;height:120px;margin-bottom:5px;" id="logoImg"/>
	         					<br/>
	         					<input type="file" name="logo" id="btnFile" style="border:none;display:inline">
	         					<button type="button" id="cxsc" style="display:inline">上传</button>
	          				<#else>
	          					<input type="file" name="logo" style="border:none">
	          				</#if>
	          			<#else>
	          				<input type="file" name="logo" style="border:none">
	          			</#if>

2.controller

@RequestMapping(value = "/uploadLogo", method = {RequestMethod.POST})
    public void uploadLogo(
        @RequestParam(value = "bankId", required = true) String bankId,
        @RequestParam("logo") MultipartFile logo,
        HttpServletRequest request, HttpServletResponse response, ModelMap model) {
		Json json = new Json();
		BankManage bankManage = bankManageService.getById(bankId);
		if (bankManage != null) {
			try {
				if (!logo.isEmpty()) {
					String relativePath = "/upload/banklogo";
					// 旧图片路径
					String absolutePath = request.getSession().getServletContext().getRealPath(relativePath)+"\"+bankManage.getLogoImg();
					File oldfile = new File(absolutePath);
					if (oldfile.exists()) {
						oldfile.delete(); // 删除旧图片
					}
					String newPath = request.getSession().getServletContext().getRealPath(relativePath)+"\"+logo.getOriginalFilename();
					File newFile = new File(newPath);
					logo.transferTo(newFile);
					bankManage.setLogoImg(logo.getOriginalFilename());
					bankManageService.update(bankManage);
					json.setMsg(logo.getOriginalFilename());
					writeJson(request, response, json);
				}else {
					json.setMsg("上传失败！");
					writeJson(request, response, json);
				}
			}catch (Exception e) {
				e.printStackTrace();
	            logger.error(e);
			}
		}
    }