Java中的FTPClient类问题

Question

我正在使用org.apache.commons.net.ftp.FTPClient，看到的行为令人困惑。

下面的方法打算浏览一个FTPFile列表，读入它们，然后对内容进行一些处理。都可以了 （真正）不起作用的是FTPClient对象执行以下操作…

1) Properly retrieves and stores the FIRST file in the list  
2) List item evaluates to NULL for x number of successive iterations of the loop (x varies on successive attempts  
3) manages to retrieve exactly 1 more file in the list  
4) reports that it is null for exactly 1 more file in the list  
5) hangs indefinitely, reporting no further activity.

public static String mergeXMLFiles(List<FTPFile> files, String rootElementNodeName, FTPClient ftp){
        String ret = null;
        String fileAsString   = null; 
        //InputStream inStream;
        int c;

        if(files == null || rootElementNodeName == null)
            return null;
        try {
            System.out.println("GETTING " + files.size() + " files");
            for (FTPFile file : files) {
                fileAsString = "";
                InputStream inStream = ftp.retrieveFileStream(file.getName());

                if(inStream == null){
                    System.out.println("FtpUtil.mergeXMLFiles() couldn't initialize inStream for file:" + file.getName());

                    continue;//THIS IS THE PART THAT I SEE FOR files [1 - arbitrary number (usually around 20)] and then 1 more time for [x + 2] after [x + 1] passes successfully.
                }
                while((c = inStream.read()) != -1){

                    fileAsString += Character.valueOf((char)c);
                }
                inStream.close();


                System.out.println("FILE:" + file.getName() + "\n" + fileAsString);
            }


        } catch (Exception e) {
            System.out.println("FtpUtil.mergeXMLFiles() failed:" + e);
        }
        return ret;
    }

有没有人看到这样的东西？我是FTPClient的新手，我在做错什么吗？

Answer 1

根据该API
FTPClient.retrieveFileStream()，该方法返回null时，它无法打开数据连接，在这种情况下，你应该检查答复代码（例如getReplyCode()，getReplyString()，getReplyStrings()），看看它为什么失败。另外，您假设通过调用completePendingCommand()并验证传输确实成功来完成文件传输。