嵌入式Apache FTP服务器：无法使用DbUserManager对客户端进行身份验证

Question

我正在尝试使用“Apache FTP Server”创建一个具有内置/嵌入式FTP服务器的应用程序。我选择从mysql数据库管理/验证用户。因此，我使用DbUserManager来处理用户创建，删除和列表。我能够管理除身份验证之外的所有用户相关操作。我无法从FTP客户端登录。服务器甚至不询问密码，只是给出消息“连接由远程主机关闭”。还有一个观察结果是 - 如果用户不在DB中，那么它要求输入密码，但最终会给出身份验证失败的消息。

这是代码，

public class Dumper {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    FtpServerFactory serverFactory;
    FtpServer server;

    ConnectionConfigFactory connectionConfigFactory;
    ConnectionConfig connectionConfig;

    DbUserManagerFactory userManagerFactory;
    DbUserManager userManager;
    BasicDataSource bdSource;

    final Map<String, Ftplet> ftpletMap;
    Ftplet ftplet;

    // TODO code application logic here
    System.out.println("I am Dumper!!");

    connectionConfigFactory = new ConnectionConfigFactory();
    connectionConfigFactory.setAnonymousLoginEnabled(true);
    connectionConfig = connectionConfigFactory.createConnectionConfig();

    ftpletMap = new HashMap<>();
    ftplet = new DumperLet();
    ftpletMap.put("default", ftplet);

    // Data Source 
    bdSource = new BasicDataSource();
    bdSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
    bdSource.setUrl("jdbc:mysql://localhost:3306/apsdma");
    bdSource.setUsername("apsdma");
    bdSource.setPassword("apsdma");

    // Database User Manager
    userManagerFactory = new DbUserManagerFactory();
    userManagerFactory.setPasswordEncryptor(new Md5PasswordEncryptor());
    userManagerFactory.setAdminName("ambedkar");

    userManagerFactory.setDataSource(bdSource);
    userManagerFactory.setSqlUserInsert("INSERT INTO FTP_USER (userid, userpassword, homedirectory, enableflag, writepermission, idletime,uploadrate, downloadrate) VALUES ('{userid}', '{userpassword}', '{homedirectory}', {enableflag}, {writepermission}, {idletime}, {uploadrate}, {downloadrate})");
    userManagerFactory.setSqlUserUpdate("UPDATE FTP_USER SET userpassword='{userpassword}', homedirectory='{homedirectory}', enableflag={enableflag}, writepermission={writepermission}, idletime={idletime}, uploadrate={uploadrate}, downloadrate={downloadrate} WHERE userid='{userid}'");
    userManagerFactory.setSqlUserDelete("DELETE FROM FTP_USER WHERE userid = '{userid}'");
    userManagerFactory.setSqlUserSelect("SELECT userid, userpassword, homedirectory, enableflag, writepermission, idletime, uploadrate, downloadrate FROM FTP_USER WHERE userid = '{userid}'");
    userManagerFactory.setSqlUserSelectAll("SELECT userid FROM FTP_USER ORDER BY userid");
    userManagerFactory.setSqlUserAdmin("SELECT userid FROM FTP_USER WHERE userid='{userid}' AND userid='ambedkar'");
    userManagerFactory.setSqlUserAuthenticate("SELECT userpassword from FTP_USER WHERE userid='{userid}'");

    userManager = (DbUserManager) userManagerFactory.createUserManager();

    serverFactory = new FtpServerFactory();
    serverFactory.setConnectionConfig(connectionConfig);
    serverFactory.setFtplets(ftpletMap);
    serverFactory.setUserManager(userManager);
    server = serverFactory.createServer();

    try {
        server.start();
    } catch (FtpException ex) {
        Logger.getLogger(Dumper.class.getName()).log(Level.SEVERE, null, ex);
        System.out.println(ex.getMessage());
    }
}
}

这是客户端输出的屏幕截图，

有人可以指导我出了什么问题或在哪里寻找解决方案，请...