java - Getting "501 Syntax error" when issuing RETR command to FTP server -

i've made ftp client have retr , list commands, have got problem. after implemented retr command keep getting error:

1:220-filezilla server version 0.9.50 beta 1:220-written tim kosse (tim.kosse@filezilla-project.org) 1:220 please visit https://filezilla-project.org/ 2331 password required geek 3230 logged on 5227 entering passive mode (127,0,0,1,217,137) 6200 type set 7150 opening data channel directory listing of "/" 5227 entering passive mode (127,0,0,1,217,139) 150 opening data channel directory listing of "/" 8501 syntax error exception in thread "main" java.net.connectexception: connection refused: connect @ java.net.dualstackplainsocketimpl.connect0(native method) @ java.net.dualstackplainsocketimpl.socketconnect(unknown source) @ java.net.abstractplainsocketimpl.doconnect(unknown source) @ java.net.abstractplainsocketimpl.connecttoaddress(unknown source) @ java.net.abstractplainsocketimpl.connect(unknown source) @ java.net.plainsocketimpl.connect(unknown source) @ java.net.sockssocketimpl.connect(unknown source) @ java.net.socket.connect(unknown source) @ java.net.socket.connect(unknown source) @ java.net.socket.<init>(unknown source) @ java.net.socket.<init>(unknown source) @ ftp.ftp.connect(ftp.java:135) @ ftp.test.main(test.java:12) 

furthermore after implemented retr command client stopped giving list command; doesn't tell files there in folder.

public class ftp{ public synchronized void connect(string host, int port, string user,         string pass) throws ioexception {     socket socket = new socket(host, port);      bufferedreader reader = new bufferedreader(new inputstreamreader(socket.getinputstream()));     bufferedwriter writer = new bufferedwriter(             new outputstreamwriter(socket.getoutputstream()));       string response = reader.readline();      if (!response.startswith("220-")) {         throw new ioexception(                 "ftp modtog et ukendt svar, da den blev forbundet til ftp server: "                         + response);     } else {system.out.println("1:"+response);     response = reader.readline();     system.out.println("1:"+response);     response = reader.readline();     system.out.println("1:"+response);       }     writer.write("user geek"+"\r\n");     writer.flush();     response= reader.readline();     system.out.println("2"+response);      writer.write("pass hello" +"\r\n");     writer.flush();     response= reader.readline();     system.out.println("3"+response);        writer.write("pasv"+"\r\n");     writer.flush();     response= reader.readline();     system.out.println("5"+response );     string [] r=response.trim().split(",");      string reg=r[4];     string add= r[5].replace(")", "");     int m = integer.parseint(reg);     int = integer.parseint(add);      int port1 = m*256+a;      socket datasocket = new socket("127.0.0.1", port1);     writer.write("type a\r\n");     writer.flush();     response= reader.readline();     system.out.println("6"+response);     bufferedreader reader2 = new bufferedreader(new inputstreamreader(datasocket.getinputstream()));       writer.write("list\r\n");     writer.flush();     response = reader.readline();     system.out.println("7" + response);      list<string> files = new arraylist<>();     string text;     while ((text = reader2.readline()) != null) {         string filename = parsefilename(text);         files.add(filename);     }     reader2.close();     datasocket.close();     reader.readline();      (string file : files) {         int passiveport = getport(reader, writer);         writer.write("retr\r\n");         writer.flush();         system.out.println(response);         byte[] mybytearray = new byte[1024];          try (socket filesocket = new socket("localhost", passiveport);                 inputstream = filesocket.getinputstream();                 fileoutputstream fos = new fileoutputstream("c:/users/username/desktop/ftp/" + file)) {             int count;             while ((count = is.read(mybytearray)) >= 0) {                 fos.write(mybytearray, 0, count);             }         }     }                  writer.write("retr\r\n");             writer.flush();             response= reader.readline();             system.out.println("8"+response);                  socket filsocket = new socket ("localhost", port1);                 inputstream = null;                 fileoutputstream fos = null;                  byte[] mybytearray = new byte[1024];             try {                     = filsocket.getinputstream();                     fos = new fileoutputstream("myfile.txt");                      int count;                     while ((count = is.read(mybytearray)) >= 0) {                         fos.write(mybytearray, 0, count);                     }                 } {                 fos.close();                     is.close();                 filsocket.close();             }  }  private string parsefilename(string text) {      return "abc.txt"; }  private int getport(bufferedreader reader, bufferedwriter writer) throws ioexception { //this line 135     string response;     writer.write("pasv" + "\r\n");     writer.flush();     response = reader.readline();     system.out.println("5" + response);     string[] r = response.trim().split(",");      string reg = r[4];     string add = r[5].replace(")", "");     int m = integer.parseint(reg);     int = integer.parseint(add);      return m * 256 + a; }   }        

thanks in advance :)

the retr command has mandatory argument specifies name of file download. how server know, file want download otherwise?

writer.write("retr " + file + "\r\n"); 

see rfc 959:

retr <sp> <pathname> <crlf> 

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anyway, why implement ftp protocol on own? use existing implementation, ftpclient apache commons.