无法使用EC2通过SFTP传输文件

Question

    String SFTPHOST = "10.20.30.40";
    int    SFTPPORT = 22;
    String SFTPUSER = "kodehelp";

    // this file can be id_rsa or id_dsa based on which algorithm is used to create the key
    String privateKey = "/home/kodehelp/.ssh/id_rsa"; 
    String SFTPWORKINGDIR = "/home/kodehelp/";

    JSch jSch = new JSch();
    Session     session     = null;
    Channel     channel     = null;
    ChannelSftp channelSftp = null;
    try {
        jSch.addIdentity(privateKey);
        System.out.println("Private Key Added.");
        session = jSch.getSession(SFTPUSER,SFTPHOST,SFTPPORT);
        System.out.println("session created.");

        java.util.Properties config = new java.util.Properties();
        config.put("StrictHostKeyChecking", "no");
        session.setConfig(config);
        session.connect();
        channel = session.openChannel("sftp");
        channel.connect();
        System.out.println("shell channel connected....");
        channelSftp = (ChannelSftp)channel;
        channelSftp.cd(SFTPWORKINGDIR);
        System.out.println("Changed the directory...");
    } catch (JSchException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (SftpException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }finally{
        if(channelSftp!=null){
            channelSftp.disconnect();
            channelSftp.exit();
        }
        if(channel!=null) channel.disconnect();

        if(session!=null) session.disconnect();
    }

我正在使用Amazon EC2通过SFTP进行文件传输。但是我无法从我的Android应用程序传输文件。请帮我解决这个问题。