public static void writeAvatarToDisk(Blob blob, String name) throws IOException {

        byte[] data = null;
        try {
            InputStream inStream = blob.getBinaryStream();
            
              BufferedImage bimage = null;                   //缓存图片对象
              BufferedInputStream ins = new BufferedInputStream(inStream);       //生成缓存输入流
              bimage=ImageIO.read(ins);                      //由ImageIO对象读成缓存图片对象。ImageIO是个很重要的对象
              FileOutputStream sos=new FileOutputStream(new File("d:/111.jpg"));
              BufferedOutputStream bos = new BufferedOutputStream(sos);    //生成输出缓存
              JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(bos);  //生成JPEG图片对象
              encoder.encode(bimage);                         //按格式把图片流进行编码
              bos.close();
              sos.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

------解决方案--------------------

我来手写一下

Blob blob = rs.getBlob("imageField");

InputStream is = blob.getInputStream();

FileOutputStream fos = new FileOutputStream("D:/a.jpg");

byte[] data = new byte[8096];
int length = 0;
while((length = is.read(data, length,8096)) != -1) {
  fos.write(data, 0 ,length);
  fos.flush();
}

fos.close();
is.close();