用socket联结ftp服务器文件传输socket

[do1doer]

我看了一下rfc文档,也就是说ftp服务器在要发送接收文件的时候是另外新建一个
临时的socket的,但是怎么知道它是哪个端口,怎么连?我试着联结服务器20端口总
失败.port,pasv命令怎么用,试什么含义?
谢谢

[caoxmby]

public class FtpLS {
public final static boolean debug = true; //true for debug trace
protected Socket ctlskt; //Control socket
protected Socket datskt; //Data socket

protected InputStream datIn; //IO Stream for data socket
protected OutputStream datOut; //IO Stream for data socket

protected BufferedReader ctlin; //Control port reader
protected OutputStream ctlout; //Control port writer

public String lastResponse; //Last response from host
public boolean passive = false; //passsive mode


public boolean connect(String host, String user, String pw)
throws UnknownHostException, IOException {
int status;
ctlskt = new Socket(host, 21);
ctlin = new BufferedReader(new InputStreamReader(ctlskt.getInputStream()));
ctlout = ctlskt.getOutputStream();
do {
status = getResponse();
} while (status != 220 && status != -1);
if (status == -1)
return false;
status = sendCmd("USER " + user);
if (status == 331)
status = sendCmd("PASS " + pw);
if (status == 332)
return false;
if (status != 230)
return false;
return true;
}
protected int dataSocket(String datCmd) throws IOException {
int port;
int status;

ServerSocket datsktsvr;
if (passive) {
StringBuffer IP = new StringBuffer();
int i;
status = sendCmd("PASV");
if (status < 200 || status > 229)
return -1;
for (i = 4; i < lastResponse.length(); i++)
if (Character.isDigit(lastResponse.charAt(i)))
break;
if (i == lastResponse.length())
return -1; //not found
StringTokenizer token = new StringTokenizer(lastResponse.substring(i), ",)");
if (token.countTokens() != 6)
return -1; //unknown IP/port
for (i = 0; i < 4; i++) {
IP.append(token.nextToken());
if (i != 3)
IP.append(".");
}
port = Integer.parseInt(token.nextToken()) * 256;
port += Integer.parseInt(token.nextToken());
datskt = new Socket(IP.toString(), port);
status = sendCmd(datCmd);
} else {
datsktsvr = new ServerSocket(0);
port = datsktsvr.getLocalPort();
//set host/port
StringBuffer cmd = new StringBuffer("PORT");
cmd.append(ctlskt.getLocalAddress().getHostAddress());
for (int i = 0; i < cmd.length(); i++) {
if ('.' == cmd.charAt(i))
cmd.setCharAt(i, ',');
}
cmd.append(",");
cmd.append(Integer.toString(port / 256));
cmd.append(",");
cmd.append(Integer.toString(port & 0xFF));
status = sendCmd(cmd.toString());
if (status != 200)
return -1;
status = sendCmd(datCmd);
//wait for remote connection
datskt = datsktsvr.accept();
}
return 0;
}
public int getFile(String filename, BFile bfile) throws IOException {
int status;
status = dataSocket("RETR " + filename);
if (status != 0)
return status;
datIn = datskt.getInputStream();

bfile.readFrom(datIn);//从IO流读取文件内容

datskt.close();
return getResponse();
}
protected int getResponse() throws IOException {
int n;
String tmp;
do {
lastResponse = ctlin.readLine();
if (debug)
Log.debug("Debug Received:" + lastResponse);
} while (lastResponse.charAt(3) == '-');
tmp = lastResponse.substring(0, 3);
try {
n = Integer.parseInt(tmp);
} catch (NumberFormatException e) {
n = -1;
}
return n;
}
protected int sendCmd(String cmd) throws IOException {
if (debug)
Log.debug("Debug Send:" + cmd);
String tmp = cmd + "\r\n";
ctlout.write(tmp.getBytes());
ctlout.flush();
return getResponse();
}
}