一般文件上传并不会放在数据库上，我这是为了测试一下咯

if ("post".equalsIgnoreCase(request.getMethod())) {        DiskFileUpload diskFileUpload = new DiskFileUpload();//文件上传的类        diskFileUpload.setHeaderEncoding("UTF-8");//设置utf-8        List
     
       list = diskFileUpload.parseRequest(request);//解析request        for (FileItem fileItem : list) {            if (!fileItem.isFormField()) {                String filename = fileItem.getName().replace("\\", "/");//                filename = filename                        .substring(filename.lastIndexOf("/") + 1);//拼接名字                Connection con = null;                PreparedStatement preparedStatement = null;                try {                    String sql = "insert into blobTest values(?,?,?)";                    con = DbManager.getConnection();                    preparedStatement = con.prepareStatement(sql);                    preparedStatement.setString(1, filename);//第一个参数和第二个参数放名字和文件类型                    preparedStatement.setString(2,                            fileItem.getContentType());                    preparedStatement.setBinaryStream(3,                            fileItem.getInputStream(),//fileItem直接打开流输入进去                            (int) fileItem.getSize());                    preparedStatement.executeUpdate();                }
     

下载类

in1 = resultSet.getBinaryStream("file");//从数据库获得字段名为file的文件

out1 = response.getOutputStream();