SpringMVC处理MySQL BLOB字段的下载

任务：

uos.docfile的content字段是longblob类型，通过Web点击链接能下载到存储在这个字段里的文件。Web点击链接类似如下形式：

http://localhost:8080/dld/downloadDocument.html?id=81&&filename=jfreechart-1.0.19.zip

1.控制器代码：

    @RequestMapping("/downloadDocument")
    public ModelAndView downloadDocument(HttpServletRequest request,HttpServletResponse response){
        try {
            // 取参数
            String id=request.getParameter("id");
            String filename=request.getParameter("filename");

            // 设置Resposne
            response.reset();
            response.setHeader("Content-disposition", "attachment; filename="+filename);
            response.setContentType("text/x-plain");

            // 获得输出流
            ServletOutputStream out = response.getOutputStream();

            // 从数据库拷贝输出流
            ByteArrayOutputStream byteOutputStream = new ByteArrayOutputStream(4096);
            service.copyDocumentOutputStream(id, byteOutputStream);
            logger.info(" call PosService.copyDocumentOutputStream successfully.");

            // 转化
            byte[] bt = null;
            bt = byteOutputStream.toByteArray();               

            // 向客户端写输出
            out.write(bt);
            out.flush();
            out.close();

            return null;
        } catch (Exception e) {
            e.printStackTrace();
            logger.error(e);

            request.setAttribute("error", e.getClass());
            request.setAttribute("reason", e.getMessage());
            StackTraceElement[] arr=e.getStackTrace();
            request.setAttribute("stackTraceElements", arr);

            return new ModelAndView("pages/error/index.jsp");
        }
    }

2.Service中代码，同样这里也只是中转

public void copyDocumentOutputStream(final String id, final OutputStream os) throws Exception{
        getPosDao().copyDocumentOutputStream(id, os);
    }

3.DAO中代码，这里是实质代码

    public void copyDocumentOutputStream(final String id, final OutputStream os) throws Exception{
        final LobHandler lobHandler=new DefaultLobHandler();

        this.getJdbcTemplate().query("select content from uos.docfile where id=?",new String[] {id},new AbstractLobStreamingResultSetExtractor(){
            protected void streamData(ResultSet rs) throws SQLException,IOException,DataAccessException{
                FileCopyUtils.copy(lobHandler.getBlobAsBinaryStream(rs,1),os);
            }
        });
    }