Getting session and SFTP channel in Java using JSch library

问题

I am using JSch library for SFTP. I need to do several operations on SFTP server like move remote files in other directory, pull files, etc. For all these operations I need Session and from it I get Channel an then cast it to ChannelSftp. This is redundant step. So I thought of abstracting it into a private method.

private ChannelSftp getChannelSftp() throws JSchException
    {
        java.util.Properties config = new java.util.Properties();
        config.put("StrictHostKeyChecking", "no");
        JSch jsch = new JSch();
        Session session;
        session = jsch.getSession(VENDOR1_USERID, VENDOR1_SERVER, VENDOR1_PORT);
        session.setPassword(VENDOR1_PASSWORD);

        session.setConfig(config);
        session.connect();

        ChannelSftp channelSftp = null;

        Channel channel = session.openChannel("sftp");
        channel.connect();
        channelSftp = (ChannelSftp) channel;

        return channelSftp;
    }

But after the SFTP operation I need to disconnect from channel and session both. With above method, though I can disconnect from Channel in the calling method but I can't disconnect from Session as I don't have its instance which might be a leak so I now separated that into getSession() method and now ChannelSftp creation is duplicated in all methods.

What is better way to design/refactor it?

private Session getSession() throws JSchException
    {
        java.util.Properties config = new java.util.Properties();
        config.put("StrictHostKeyChecking", "no");
        JSch jsch = new JSch();
        Session session;
        session = jsch.getSession(VENDOR1_USERID, VENDOR1_SERVER, VENDOR1_PORT);
        session.setPassword(VENDOR1_PASSWORD);
        session.setConfig(config);
        session.connect();
        return session;
    }

Calling Method example: - Duplicated code indicated

public void sftp(File file) throws  SftpException, FileNotFoundException, JSchException
    {
        Session session = getSession();
/* Duplicate code START*/
        if ( session == null ) throw new SftpException(0 , "Service: Session is NULL"); 

        ChannelSftp channelSftp = null;

        Channel channel = session.openChannel("sftp");
        channel.connect();
        channelSftp = (ChannelSftp) channel;
/* Duplicate code END*/
        channelSftp.cd(VENDOR1_PATH);
        channelSftp.put(new FileInputStream(file), file.getName());

        channelSftp.disconnect();
        session.disconnect();
    }

回答1:

If you use the SFTP session frequently enough, you should not recreate it for every operation. Opening an SSH/SFTP connection is very CPU demanding, both for the client and the server. It's quite a waste to shutdown a connection, if you are going to need a new one shortly.

So consider opening a single shared session and channel at the beginning of your "application" and reuse it for all operations.

---

To answer your actual session: I'd introduce another class that owns both Session and ChannelSftp (with methods like getSession() and getChannel()) and return that from the factory method.

---

Though actually, there's getSession method in the Channel class.

来源：https://stackoverflow.com/questions/47451879/getting-session-and-sftp-channel-in-java-using-jsch-library