用java实现文件上载 解压后提示文件头？被破坏 不可预料的压缩文件末端 请教如何解决

public static void downLoadZipAndRar(HttpServletRequest request,            HttpServletResponse response, String fileName) throws Exception,            NullPointerException {                String prjId = request.getParameter("prjId");        if(prjId!=null||!"".equals(prjId)){            PubDataManager.downloadAdd(prjId);            StringBuffer redirectString = new StringBuffer();            redirectString.append(PubDataManager.getPubDataManager().getPubResourceDesc(Constants.RSC_DOWNLOAD_HOST))            .append("prjInfo/")            .append(fileName);            response.sendRedirect(response.encodeRedirectURL(redirectString.toString()));            return;        }        String filePath = request.getSession().getServletContext().getRealPath(                "/download/prjInfo");        String codePrjStr = request.getParameter("codePrjId");        if(codePrjStr != null && !"".equals(codePrjStr)) {            long codePrjId = Long.parseLong(request.getParameter("codePrjId"));            String code_prj_flag = request.getParameter("code_prj_flag");            if(code_prj_flag != null && !"".equals(code_prj_flag) && code_prj_flag.equals("cpflag")) {                String rootPath = request.getSession().getServletContext().getRealPath("/");                filePath = rootPath.replaceAll("ruancu", "ruanko");                filePath += WebappUtil.getCodePrjZipDir(codePrjId);            }        }                BufferedOutputStream bos = null;        BufferedInputStream bis  = null;        StringBuffer sb = new StringBuffer(50);        sb.append("attachment;  filename=");        sb.append(fileName);                try {            if (fileName != null) {                response.reset();                response.setContentType("application/msword");                response.setHeader("Content-Disposition", new String(sb                        .toString().getBytes(), "ISO8859-1"));                String tmp = filePath + "/" + fileName;                File file = new File(tmp);                bis = new BufferedInputStream(                        new FileInputStream(tmp));                int i;                byte buffer[] = new byte[1024];                if (file.exists()) {                    bos = new BufferedOutputStream(response.getOutputStream());                    while ((i = bis.read(buffer)) != -1) {                        bos.write(buffer, 0, i);                    }                    bos.flush();                    }            }        } catch (Exception e) {            if(log.isDebugEnabled()){                log.debug(fileName + " download was interruppt!", e);            }        }finally{            try {                if (bis != null) {                    bis.close();                }            } catch (Exception e) {            }            try {                if (bos != null) {                    bos.close();                }            } catch (Exception e) {            }        }    }