利用ajax上传文件

<input type="file" id="file"><br/>
<button class="btn btn-danger"  id="btn_upload_excel"> 上传</button>

$("#btn_upload_excel").click(function () {
    var fileObj =document.getElementById('file').files; // js 获取文件对象
    if (typeof (fileObj) == "undefined" || fileObj.size <= 0) {
        alert("请选择文件");
        return;
    }
    var formFile = new FormData();
    //formFile.append("action", "emp/import");
    formFile.append("excel_file", fileObj[0]); //加入文件对象

    var data = formFile;
    $.ajax({
        url: "emp/import",
        data: data,
        type: "Post",
        dataType: "json",
        cache: false,//上传文件无需缓存
        processData: false,//用于对data参数进行序列化处理 这里必须false
        contentType: false, //必须
        success: function (result) {
            alert("上传完成!");
        },
    })
})

java后台：
@RequestMapping(value = "/emp/import", method = RequestMethod.POST)
public void importExcel(@RequestParam("excel_file") MultipartFile files, HttpServletRequest request, HttpServletResponse response) throws Exception {

    String fileName = null;
    String tempPath=null;
    try {
        fileName = files.getOriginalFilename();
        byte[] bytes = files.getBytes();
        String savePath = request.getServletContext().getRealPath("/WEB-INF/upload");
        //上传时生成的临时文件保存目录
        tempPath = request.getServletContext().getRealPath("/WEB-INF/temp");
        File tmpFile = new File(tempPath);
        if (!tmpFile.exists()) {
            //创建临时目录
            tmpFile.mkdir();
        }
        BufferedOutputStream buffStream = new BufferedOutputStream(new FileOutputStream(new File(tempPath + fileName)));
        buffStream.write(bytes);
        buffStream.close();
    } catch (Exception e) {
        throw new Exception( "You failed to upload " + fileName + ": " + e.getMessage());
    }
}