Android FTP下载损坏

Question

我通过FileZilla将.db文件上传到我的FTP服务器。然后我写了一些代码，使用Apache ftp commons将文件下载到我的设备。在我下载并尝试查询后，它会一直显示错误。然后我发现下载文件的文件大小只是0.我不知道发生了什么，因为这是我第一次处理FTP问题。

下载代码如下所示。

public void run() {
            //Download the database here
            String networkName="abc.net";
            //User name and password. CONFIDENTIAL!
            String user="a1234";
            String pw="123455";
            String dir="/public_html/word_enhancement_db.db";
            FTPClient client=new FTPClient();
try{
                //Connect the server and log in.
                client.connect(networkName);
                if (client.login(user,pw))
                    Log.w("InternetThread","Logged in");
                else Log.w("InternetThread","Cannot log in!");

                //Set the location for the database.
                String DB_PATH="/data/data/com.android.luftschlafer.wordenhancement/databases";
                String DB_NAME="/word_enhancement.db";
                Log.w("DB location",DB_PATH+DB_NAME);
                Log.w("InternetThread", "Old DB not found");
                    File newDB = new File(DB_PATH, DB_NAME);
                    if (newDB.mkdirs()) {
                        Log.w("InternetThread", "New DB dir has been produced");
                    }
                    Log.w("InternetThread", "New DB has been built");
                    FileOutputStream fos = new FileOutputStream(DB_PATH + DB_NAME);
                    client.setBufferSize(1024);
                    client.setFileType(FTP.BINARY_FILE_TYPE);
                    client.retrieveFile(dir, fos);

                    fos.close();
                    Log.w("InternetThread", "New database has been written");
                    Log.w("InternetThread"," New database file size: "+Long.toString(newDB.length()));
                }
            } catch (Exception e){
                e.printStackTrace();
                Log.e("InternetThread","Client connection error");
            } finally {
                try{
                    client.disconnect();
                    Log.w("InternetThread","Logged out");
                } catch (Exception e){
                    e.printStackTrace();
                    Log.w("InternetThread","Cannot disconnect");
                }
            }