java IO流下载.xlsx .docx 文件时报文件损坏的错误修复

由于用IO流下载.xlsx .docx 文件时报文件损坏的错误修复，找了半天原因，终于解决了，记录一下原因，以及解决方案
一.出现损坏的原因：
并不是每次都能读到1024个字节，所有用len作为每次读取数据的长度，否则会出现文件损坏的错误

二.解决方法（注意红的部分代码）
1.原本文件下载代码如下：
public void Downloads(HttpServletResponse response , String url){
    try {

        File file = new File(url);
        String str = new SimpleDateFormat("yyyyMMddHHmmss").format(new Date());
        String name=str+".xlsx";
        if(file.exists()){ //判断文件父目录是否存在
            response.setContentType("application/force-download");
            response.setHeader("Content-Disposition", "attachment;fileName=" + URLEncoder.encode(name, "UTF-8"));
            response.setHeader("Pragma", URLEncoder.encode(name, "UTF-8"));
            byte[] buffer = new byte[1024];
            FileInputStream fis = null; //文件输入流
            BufferedInputStream bis = null;
            OutputStream os = null; //输出流
            os = response.getOutputStream();
            fis = new FileInputStream(file);
            bis = new BufferedInputStream(fis);
            while(bis.read(buffer) != -1){
                os.write(buffer);
            }
            bis.close();
            fis.close();
        }
    }catch (Exception e){
        e.printStackTrace();
        logger.warn("sys:zydownload:Downloads--userId:"+ ShiroUtils.getUserId()+"===="+e.getMessage());
    }
}
注：这种写法会出现IO流下载.xlsx .docx 文件时报文件损坏的错误修复，改成下面的写法则可以解决

2.改进后的代码

public void Downloads(HttpServletResponse response , String url){
    try {
        File file = new File(url);
        String str = new SimpleDateFormat("yyyyMMddHHmmss").format(new Date());
        String name=str+".xlsx";
        if(file.exists()){ //判断文件父目录是否存在
            response.setCharacterEncoding("UTF-8");
            response.setHeader("content-Type", "application/vnd.ms-excel");
            response.setHeader("Content-Disposition", "attachment;fileName=" + URLEncoder.encode(name, "UTF-8"));
            response.setHeader("Pragma", URLEncoder.encode(name, "UTF-8"));
            byte[] buffer = new byte[1024];
            FileInputStream fis = null; //文件输入流
            BufferedInputStream bis = null;
            OutputStream os = null; //输出流
            os = response.getOutputStream();
            fis = new FileInputStream(file);
            bis = new BufferedInputStream(fis);

            int len = 0; while((len = bis.read(buffer)) >0){ os.write(buffer, 0, len); }
            bis.close();
            fis.close();
        }
    }catch (Exception e){
        e.printStackTrace();
        logger.warn("sys:zydownload:Downloads--userId:"+ ShiroUtils.getUserId()+"===="+e.getMessage());
    }
}