解决EasyPoi导出Excel文件后提示无法打开文件的问题

本来项目中导出Excel文件借助EasyPoi用得好好的，今天测试时发现对要导出的数据做了筛选后，导出的Excel文件打开就会弹出“无法打开文件”的提示，如图所示：

 经过网上寻找答案，发现问题出在downLoadExcel这个方法里，原代码如下：

/**
     * excel下载
     *
     * @param fileName 下载时的文件名称
     * @param response
     * @param workbook excel数据
     */
    private static void downLoadExcel(String fileName, HttpServletResponse response, Workbook workbook) throws IOException {
        try {
            response.setCharacterEncoding("UTF-8");
            response.setHeader("content-Type", "application/vnd.ms-excel");
            response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName + ".xls", "UTF-8"));
            workbook.write(response.getOutputStream());
        } catch (Exception e) {
            throw new IOException(e.getMessage());
        }
    }

修改后的代码：

/**
     * excel下载
     *
     * @param fileName 下载时的文件名称
     * @param response
     * @param workbook excel数据
     */
    private static void downLoadExcel(String fileName, HttpServletResponse response, Workbook workbook) throws IOException {
        try (OutputStream out = response.getOutputStream()) {
            response.setCharacterEncoding("UTF-8");
            response.setHeader("content-Type", "application/vnd.ms-excel");
            response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName + ".xls", "UTF-8"));
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            workbook.write(baos);
            response.setHeader("Content-Length", String.valueOf(baos.size()));
            out.write( baos.toByteArray() );
        } catch (Exception e) {
            try {
                throw new Exception(e.getMessage());
            } catch (Exception e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
        }
    }

问题原因：请求头的Content-Length，在未设置的情况在是-1，下载时需重新定义Content-Length