Writing a Java FTP server

Question

I am trying to write a code that opens an FTP server on my stand-alone so I could copy file from it to a client in another computer and the opposite, but I am very new to server side programming and don't understand how.

I got the Apache FtpServer but got a little confused with it's use, and am looking for the basic steps of how to use it. Maybe something like:

1. do connect command
2. login
3. do some things....

Answer 1

Let me write a basic example for you, using the very useful Apache FtpServer:

FtpServerFactory serverFactory = new FtpServerFactory(); ListenerFactory factory = new ListenerFactory(); factory.setPort(1234);// set the port of the listener (choose your desired port, not 1234) serverFactory.addListener("default", factory.createListener()); PropertiesUserManagerFactory userManagerFactory = new PropertiesUserManagerFactory(); userManagerFactory.setFile(new File("/home/blablah/myusers.properties"));//choose any. We're telling the FTP-server where to read its user list userManagerFactory.setPasswordEncryptor(new PasswordEncryptor() {//We store clear-text passwords in this example          @Override         public String encrypt(String password) {             return password;         }          @Override         public boolean matches(String passwordToCheck, String storedPassword) {             return passwordToCheck.equals(storedPassword);         }     });     //Let's add a user, since our myusers.properties file is empty on our first test run     BaseUser user = new BaseUser();     user.setName("test");     user.setPassword("test");     user.setHomeDirectory("/home/blablah");     List<Authority> authorities = new ArrayList<Authority>();     authorities.add(new WritePermission());     user.setAuthorities(authorities);     UserManager um = userManagerFactory.createUserManager();     try     {         um.save(user);//Save the user to the user list on the filesystem     }     catch (FtpException e1)     {         //Deal with exception as you need     }     serverFactory.setUserManager(um);     Map<String, Ftplet> m = new HashMap<String, Ftplet>();     m.put("miaFtplet", new Ftplet()     {          @Override         public void init(FtpletContext ftpletContext) throws FtpException {             //System.out.println("init");             //System.out.println("Thread #" + Thread.currentThread().getId());         }          @Override         public void destroy() {             //System.out.println("destroy");             //System.out.println("Thread #" + Thread.currentThread().getId());         }          @Override         public FtpletResult beforeCommand(FtpSession session, FtpRequest request) throws FtpException, IOException         {             //System.out.println("beforeCommand " + session.getUserArgument() + " : " + session.toString() + " | " + request.getArgument() + " : " + request.getCommand() + " : " + request.getRequestLine());             //System.out.println("Thread #" + Thread.currentThread().getId());              //do something             return FtpletResult.DEFAULT;//...or return accordingly         }          @Override         public FtpletResult afterCommand(FtpSession session, FtpRequest request, FtpReply reply) throws FtpException, IOException         {             //System.out.println("afterCommand " + session.getUserArgument() + " : " + session.toString() + " | " + request.getArgument() + " : " + request.getCommand() + " : " + request.getRequestLine() + " | " + reply.getMessage() + " : " + reply.toString());             //System.out.println("Thread #" + Thread.currentThread().getId());              //do something             return FtpletResult.DEFAULT;//...or return accordingly         }          @Override         public FtpletResult onConnect(FtpSession session) throws FtpException, IOException         {             //System.out.println("onConnect " + session.getUserArgument() + " : " + session.toString());             //System.out.println("Thread #" + Thread.currentThread().getId());              //do something             return FtpletResult.DEFAULT;//...or return accordingly         }          @Override         public FtpletResult onDisconnect(FtpSession session) throws FtpException, IOException         {             //System.out.println("onDisconnect " + session.getUserArgument() + " : " + session.toString());             //System.out.println("Thread #" + Thread.currentThread().getId());              //do something             return FtpletResult.DEFAULT;//...or return accordingly         }     });     serverFactory.setFtplets(m);     //Map<String, Ftplet> mappa = serverFactory.getFtplets();     //System.out.println(mappa.size());     //System.out.println("Thread #" + Thread.currentThread().getId());     //System.out.println(mappa.toString());     FtpServer server = serverFactory.createServer();     try     {         server.start();//Your FTP server starts listening for incoming FTP-connections, using the configuration options previously set     }     catch (FtpException ex)     {         //Deal with exception as you need     } 

Note that, server-side, you don't have to deal manually with connects, logins, etc: the Ftplet does that for you.

You can, however, add your custom pre[or post]-processing inside the overridden methods of your anonymous inner Ftplet class (when you instantiate it with new Ftplet(){ ... }.