Question

我需要Java代码来从CSV格式下载数据库中的特定行。我正在使用Netbeans IDE和Structs。

我在动作类中使用了以下代码：

else if (mode.equalsIgnoreCase("download"))
{
    if(null !=request.getParameter("batchid")){
        batch_id=request.getParameter("batchid");
    }
     UploadVO uploadvo= new UploadVO();          
        filetype = uploadform.getFiletype();
        filename = uploadform.getFilename(); 
    try{
        String sqls = "select ROW_NUMBER() over(order by id) as  row,trx_batch_id,account_id,"
                    + "(select name from [user] where id=tt.user_id) as Uploadedby,(SELECT CONVERT(VARCHAR(10),GETDATE(),101) ) as date_of_transaction,"
                    + "amount,(select description from [_transaction_type] where type=tt.type) as type,note,reverse_transaction_id from"
                    + " [transaction] tt  "+ "where trx_batch_id= '" +batch_id+ "'" ;

            Statement stmts = con.createStatement();

            ResultSet rss = stmts.executeQuery(sqls);
            while (rss.next()) {

            byte[] ba;
            Blob b = rss.getBlob("content");
            ba = b.getBytes(1, (int) b.length());
            uploadvo.setDocfile(ba);
            }
    }
    catch(Exception e){

    }
   if (filetype.trim().equalsIgnoreCase("text/plain")) {
        response.setContentType("text/plain");
    } else if (filetype.trim().equalsIgnoreCase("application/ms-doc")) {
        response.setContentType("application/ms-doc");
    } else if (filetype.trim().equalsIgnoreCase("application/ms-excel")) {
        response.setContentType("application/ms-excel");
    } else if (filetype.trim().equalsIgnoreCase("pdf")) {
        response.setContentType("application/pdf");
    } else if (filetype.trim().equalsIgnoreCase("ppt")) {
        response.setContentType("application/ppt");
    } else if (filetype.trim().equalsIgnoreCase("application/vnd.ms-excel")) {
        response.setContentType("application/vnd.ms-excel");
    } else if (filetype.trim().equalsIgnoreCase("image/jpeg")) {
        response.setContentType("image/jpeg");
    } else {
        response.setContentType("application/octet-stream");
    }


    String disHeader = "Attachment; Filename= " + filename + "";
    System.out.println(disHeader);
    response.setHeader("Content-Disposition", disHeader);
    response.setHeader("cache-control", "no-cache");

    ServletOutputStream outs = response.getOutputStream();
    outs.write(uploadvo.getDocfile());
    outs.flush();
    outs.close();
    return mapping.findForward("success");

}

但我得到一个空指针异常。

Answer 1

您正在调用fileType.trim()而不检查它是否为空。

你不要求的东西，但应该被提及。

Apache Commons有一个StringUtils类，非常适合检查字符串是否为空，所以不要写

if (null !=request.getParameter("batchid"))

你会写

if (StringUtils.isNotEmpty(request.getParameter("batchid"))

因为你可能有兴趣知道它是否包含空格。

另外，你的

else if (mode.equalsIgnoreCase("download"))

表示您正在启用mode（我不确定您是否已检查null）。在struts 1.x中，您可以使用DispatchAction来指定参数，例如mode，它将是被调用方法的名称，因此在您的示例中，您将实现一个方法

public ActionForward download(...) {
...
}

将在"download".equals(request.getParameter("mode")时调用。

另请注意，编写"download".equals(request.getParameter("mode")而不是request.getParameter("mode").equals("download")可以使您免于潜在的空指针

从struts中的csv文件中下载数据库中的特定行

1 个答案: