org.apache.commons.net.ftp
public class FTPClient extends FTP implements Configurable
boolean error = false; try { int reply; ftp.connect("ftp.foobar.com"); System.out.println("Connected to " + server + "."); System.out.print(ftp.getReplyString()); // After connection attempt, you should check the reply code to verify // success. reply = ftp.getReplyCode(); if(!FTPReply.isPositiveCompletion(reply)) { ftp.disconnect(); System.err.println("FTP server refused connection."); System.exit(1); } ... // transfer files ftp.logout(); } catch(IOException e) { error = true; e.printStackTrace(); } finally { if(ftp.isConnected()) { try { ftp.disconnect(); } catch(IOException ioe) { // do nothing } } System.exit(error ? 1 : 0); }
Immediately after connecting is the only real time you need to check the reply code (because connect is of type void). The convention for all the FTP command methods in FTPClient is such that they either return a boolean value or some other value. The boolean methods return true on a successful completion reply from the FTP server and false on a reply resulting in an error condition or failure. The methods returning a value other than boolean return a value containing the higher level data produced by the FTP command, or null if a reply resulted in an error condition or failure. If you want to access the exact FTP reply code causing a success or failure, you must call {@link org.apache.commons.net.ftp.FTP#getReplyCode getReplyCode } after a success or failure.
The default settings for FTPClient are for it to use
FTP.ASCII_FILE_TYPE
,
FTP.NON_PRINT_TEXT_FORMAT
,
FTP.STREAM_TRANSFER_MODE
, and
FTP.FILE_STRUCTURE
. The only file types directly supported
are FTP.ASCII_FILE_TYPE
and
FTP.IMAGE_FILE_TYPE
(which is the same as
FTP.BINARY_FILE_TYPE
). Because there are at lest 4
different EBCDIC encodings, we have opted not to provide direct support
for EBCDIC. To transfer EBCDIC and other unsupported file types you
must create your own filter InputStreams and OutputStreams and wrap
them around the streams returned or required by the FTPClient methods.
FTPClient uses the {@link ToNetASCIIOutputStream NetASCII}
filter streams to provide transparent handling of ASCII files. We will
consider incorporating EBCDIC support if there is enough demand.
FTP.NON_PRINT_TEXT_FORMAT
,
FTP.STREAM_TRANSFER_MODE
, and
FTP.FILE_STRUCTURE
are the only supported formats,
transfer modes, and file structures.
Because the handling of sockets on different platforms can differ significantly, the FTPClient automatically issues a new PORT command prior to every transfer requiring that the server connect to the client's data port. This ensures identical problem-free behavior on Windows, Unix, and Macintosh platforms. Additionally, it relieves programmers from having to issue the PORT command themselves and dealing with platform dependent issues.
Additionally, for security purposes, all data connections to the client are verified to ensure that they originated from the intended party (host and port). If a data connection is initiated by an unexpected party, the command will close the socket and throw an IOException. You may disable this behavior with {@link #setRemoteVerificationEnabled setRemoteVerificationEnabled()}.
You should keep in mind that the FTP server may choose to prematurely
close a connection if the client has been idle for longer than a
given time period (usually 900 seconds). The FTPClient class will detect a
premature FTP server connection closing when it receives a
{@link org.apache.commons.net.ftp.FTPReply#SERVICE_NOT_AVAILABLE FTPReply.SERVICE_NOT_AVAILABLE }
response to a command.
When that occurs, the FTP class method encountering that reply will throw
an {@link org.apache.commons.net.ftp.FTPConnectionClosedException}
.
FTPConnectionClosedException
is a subclass of IOException
and therefore need not be
caught separately, but if you are going to catch it separately, its
catch block must appear before the more general IOException
catch block. When you encounter an
{@link org.apache.commons.net.ftp.FTPConnectionClosedException}
, you must disconnect the connection with
{@link #disconnect disconnect() } to properly clean up the
system resources used by FTPClient. Before disconnecting, you may check the
last reply code and text with
{@link org.apache.commons.net.ftp.FTP#getReplyCode getReplyCode },
{@link org.apache.commons.net.ftp.FTP#getReplyString getReplyString },
and
{@link org.apache.commons.net.ftp.FTP#getReplyStrings getReplyStrings}.
You may avoid server disconnections while the client is idle by
periodicaly sending NOOP commands to the server.
Rather than list it separately for each method, we mention here that every method communicating with the server and throwing an IOException can also throw a {@link org.apache.commons.net.MalformedServerReplyException} , which is a subclass of IOException. A MalformedServerReplyException will be thrown when the reply received from the server deviates enough from the protocol specification that it cannot be interpreted in a useful manner despite attempts to be as lenient as possible.
Listing API Examples Both paged and unpaged examples of directory listings are available, as follows:
Unpaged (whole list) access, using a parser accessible by auto-detect:
FTPClient f=FTPClient(); f.connect(server); f.login(username, password); FTPFile[] files = listFiles(directory);
Paged access, using a parser not accessible by auto-detect. The class defined in the first parameter of initateListParsing should be derived from org.apache.commons.net.FTPFileEntryParser:
FTPClient f=FTPClient(); f.connect(server); f.login(username, password); FTPListParseEngine engine = f.initiateListParsing("com.whatever.YourOwnParser", directory); while (engine.hasNext()) { FTPFile[] files = engine.getNext(25); // "page size" you want //do whatever you want with these files, display them, etc. //expensive FTPFile objects not created until needed. }
Paged access, using a parser accessible by auto-detect:
FTPClient f=FTPClient(); f.connect(server); f.login(username, password); FTPListParseEngine engine = f.initiateListParsing(directory); while (engine.hasNext()) { FTPFile[] files = engine.getNext(25); // "page size" you want //do whatever you want with these files, display them, etc. //expensive FTPFile objects not created until needed. }
For examples of using FTPClient on servers whose directory listings
MM d yyyy
NOTE: If you experience problems with unwanted firing of
setSoTimeout()during periods of client inactivity, this can be alleviated by calling
setReaderThread(false). For more details, see this thread.
See Also: FTP FTPConnectionClosedException FTPFileEntryParser FTPFileEntryParserFactory DefaultFTPFileEntryParserFactory FTPClientConfig
Field Summary | |
---|---|
static int | ACTIVE_LOCAL_DATA_CONNECTION_MODE
A constant indicating the FTP session is expecting all transfers
to occur between the client (local) and server and that the server
should connect to the client's data port to initiate a data transfer.
|
static int | ACTIVE_REMOTE_DATA_CONNECTION_MODE
A constant indicating the FTP session is expecting all transfers
to occur between two remote servers and that the server
the client is connected to should connect to the other server's
data port to initiate a data transfer.
|
static int | PASSIVE_LOCAL_DATA_CONNECTION_MODE
A constant indicating the FTP session is expecting all transfers
to occur between the client (local) and server and that the server
is in passive mode, requiring the client to connect to the
server's data port to initiate a transfer.
|
static int | PASSIVE_REMOTE_DATA_CONNECTION_MODE
A constant indicating the FTP session is expecting all transfers
to occur between two remote servers and that the server
the client is connected to is in passive mode, requiring the other
server to connect to the first server's data port to initiate a data
transfer.
|
Constructor Summary | |
---|---|
FTPClient()
Default FTPClient constructor. |
Method Summary | |
---|---|
boolean | abort()
Abort a transfer in progress.
|
boolean | allocate(int bytes)
Reserve a number of bytes on the server for the next file transfer.
|
boolean | allocate(int bytes, int recordSize)
Reserve space on the server for the next file transfer.
|
boolean | appendFile(String remote, InputStream local)
Appends to a file on the server with the given name, taking input
from the given InputStream. |
OutputStream | appendFileStream(String remote)
Returns an OutputStream through which data can be written to append
to a file on the server with the given name. |
boolean | changeToParentDirectory()
Change to the parent directory of the current working directory.
|
boolean | changeWorkingDirectory(String pathname)
Change the current working directory of the FTP session.
|
boolean | completePendingCommand()
There are a few FTPClient methods that do not complete the
entire sequence of FTP commands to complete a transaction. |
void | configure(FTPClientConfig config)
Implementation of the {@link Configurable Configurable} interface.
|
FTPFileList | createFileList(FTPFileEntryParser parser)
Using a programmer specified FTPFileEntryParser ,
initialize an object containing a raw file information for the
current working directory. |
FTPFileList | createFileList(String pathname, FTPFileEntryParser parser)
Using a programmer specified FTPFileEntryParser ,
initialize an object containing a raw file information for a directory
or information for a single file. |
boolean | deleteFile(String pathname)
Deletes a file on the FTP server.
|
void | disconnect()
Closes the connection to the FTP server and restores
connection parameters to the default values.
|
void | enterLocalActiveMode()
Set the current data connection mode to
ACTIVE_LOCAL_DATA_CONNECTION_MODE . |
void | enterLocalPassiveMode()
Set the current data connection mode to
PASSIVE_LOCAL_DATA_CONNECTION_MODE . |
boolean | enterRemoteActiveMode(InetAddress host, int port)
Set the current data connection mode to
ACTIVE_REMOTE_DATA_CONNECTION . |
boolean | enterRemotePassiveMode()
Set the current data connection mode to
PASSIVE_REMOTE_DATA_CONNECTION_MODE . |
int | getBufferSize()
Retrieve the current internal buffer size. |
int | getDataConnectionMode()
Returns the current data connection mode (one of the
_DATA_CONNECTION_MODE constants.
|
String | getPassiveHost()
Returns the hostname or IP address (in the form of a string) returned
by the server when entering passive mode. |
int | getPassivePort()
If in passive mode, returns the data port of the passive host.
|
long | getRestartOffset()
Fetches the restart offset.
|
String | getStatus()
Issue the FTP STAT command to the server.
|
String | getStatus(String pathname)
Issue the FTP STAT command to the server for a given pathname. |
String | getSystemName()
Fetches the system type name from the server and returns the string.
|
FTPListParseEngine | initiateListParsing()
Using the default autodetect mechanism, initialize an FTPListParseEngine
object containing a raw file information for the current working
directory on the server
This information is obtained through the LIST command. |
FTPListParseEngine | initiateListParsing(String pathname)
Using the default autodetect mechanism, initialize an FTPListParseEngine
object containing a raw file information for the supplied directory.
|
FTPListParseEngine | initiateListParsing(String parserKey, String pathname)
Using the supplied parser key, initialize an FTPListParseEngine
object containing a raw file information for the supplied directory.
|
boolean | isRemoteVerificationEnabled()
Return whether or not verification of the remote host participating
in data connections is enabled. |
FTPFile[] | listFiles(String parserKey, String pathname)
Using the supplied parserKey , obtain a list
of file information for the current working directory or for just a
single file.
|
FTPFile[] | listFiles(String pathname)
Using the default system autodetect mechanism, obtain a
list of file information for the current working directory
or for just a single file.
|
FTPFile[] | listFiles()
Using the default system autodetect mechanism, obtain a
list of file information for the current working directory.
|
FTPFile[] | listFiles(FTPFileListParser parser, String pathname)
Using a programmer specified FTPFileListParser , obtain a
list of file information for a directory or information for
just a single file. |
FTPFile[] | listFiles(FTPFileListParser parser)
Using a programmer specified FTPFileListParser ,
obtain a list of file information for the current working directory.
|
String | listHelp()
Fetches the system help information from the server and returns the
full string.
|
String | listHelp(String command)
Fetches the help information for a given command from the server and
returns the full string. |
String[] | listNames(String pathname)
Obtain a list of filenames in a directory (or just the name of a given
file, which is not particularly useful). |
String[] | listNames()
Obtain a list of filenames in the current working directory
This information is obtained through the NLST command. |
boolean | login(String username, String password)
Login to the FTP server using the provided username and password.
|
boolean | login(String username, String password, String account)
Login to the FTP server using the provided username, password,
and account. |
boolean | logout()
Logout of the FTP server by sending the QUIT command.
|
boolean | makeDirectory(String pathname)
Creates a new subdirectory on the FTP server in the current directory
(if a relative pathname is given) or where specified (if an absolute
pathname is given).
|
String | printWorkingDirectory()
Returns the pathname of the current working directory.
|
boolean | remoteAppend(String filename)
Initiate a server to server file transfer. |
boolean | remoteRetrieve(String filename)
Initiate a server to server file transfer. |
boolean | remoteStore(String filename)
Initiate a server to server file transfer. |
boolean | remoteStoreUnique(String filename)
Initiate a server to server file transfer. |
boolean | remoteStoreUnique()
Initiate a server to server file transfer. |
boolean | removeDirectory(String pathname)
Removes a directory on the FTP server (if empty).
|
boolean | rename(String from, String to)
Renames a remote file.
|
boolean | retrieveFile(String remote, OutputStream local)
Retrieves a named file from the server and writes it to the given
OutputStream. |
InputStream | retrieveFileStream(String remote)
Returns an InputStream from which a named file from the server
can be read. |
boolean | sendNoOp()
Sends a NOOP command to the FTP server. |
boolean | sendSiteCommand(String arguments)
Send a site specific command. |
void | setBufferSize(int bufSize)
Set the internal buffer size.
|
void | setDataTimeout(int timeout)
Sets the timeout in milliseconds to use when reading from the
data connection. |
boolean | setFileStructure(int structure)
Sets the file structure. |
boolean | setFileTransferMode(int mode)
Sets the transfer mode. |
boolean | setFileType(int fileType)
Sets the file type to be transferred. |
boolean | setFileType(int fileType, int formatOrByteSize)
Sets the file type to be transferred and the format. |
void | setParserFactory(FTPFileEntryParserFactory parserFactory)
set the factory used for parser creation to the supplied factory object.
|
void | setRemoteVerificationEnabled(boolean enable)
Enable or disable verification that the remote host taking part
of a data connection is the same as the host to which the control
connection is attached. |
void | setRestartOffset(long offset)
Sets the restart offset. |
boolean | storeFile(String remote, InputStream local)
Stores a file on the server using the given name and taking input
from the given InputStream. |
OutputStream | storeFileStream(String remote)
Returns an OutputStream through which data can be written to store
a file on the server using the given name. |
boolean | storeUniqueFile(String remote, InputStream local)
Stores a file on the server using a unique name derived from the
given name and taking input
from the given InputStream. |
boolean | storeUniqueFile(InputStream local)
Stores a file on the server using a unique name assigned by the
server and taking input from the given InputStream. |
OutputStream | storeUniqueFileStream(String remote)
Returns an OutputStream through which data can be written to store
a file on the server using a unique name derived from the given name.
|
OutputStream | storeUniqueFileStream()
Returns an OutputStream through which data can be written to store
a file on the server using a unique name assigned by the server.
|
boolean | structureMount(String pathname)
Issue the FTP SMNT command.
|
protected void | _connectAction_() |
protected Socket | _openDataConnection_(int command, String arg)
Establishes a data connection with the FTP server, returning
a Socket for the connection if successful. |
ACTIVE_LOCAL_DATA_CONNECTION_MODE
, the file type
set to FTP.ASCII_FILE_TYPE
, the
file format set to FTP.NON_PRINT_TEXT_FORMAT
,
the file structure set to FTP.FILE_STRUCTURE
, and
the transfer mode set to FTP.STREAM_TRANSFER_MODE
.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: bytes The number of bytes which the server should allocate.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: bytes The number of bytes which the server should allocate. recordSize The size of a file record.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: remote The name of the remote file. local The local InputStream from which to read the data to be appended to the remote file.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. CopyStreamException If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: remote The name of the remote file.
Returns: An OutputStream through which the remote file can be appended. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: pathname The new current working directory.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
For example,
InputStream input; OutputStream output; input = new FileInputStream("foobaz.txt"); output = ftp.storeFileStream("foobar.txt") if(!FTPReply.isPositiveIntermediate(ftp.getReplyCode())) { input.close(); output.close(); ftp.logout(); ftp.disconnect(); System.err.println("File transfer failed."); System.exit(1); } Util.copyStream(input, output); input.close(); output.close(); // Must call completePendingCommand() to finish command. if(!ftp.completePendingCommand()) { ftp.logout(); ftp.disconnect(); System.err.println("File transfer failed."); System.exit(1); }
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: config {@link FTPClientConfig FTPClientConfig} object used to provide non-standard configurations to the parser.
Since: 1.4
Deprecated: - use initiateListParsing(FTPFileEntryParser) method instead.
Using a programmer specified FTPFileEntryParser
,
initialize an object containing a raw file information for the
current working directory. This information is obtained through
the LIST command. This object is then capable of being iterated to
return a sequence of FTPFile objects with information filled in by the
FTPFileEntryParser
used.
The server may or may not expand glob expressions. You should avoid using glob expressions because the return format for glob listings differs from server to server and will likely cause this method to fail.
This method differs from using the listFiles() methods in that expensive FTPFile objects are not created until needed which may be an advantage on large lists.
Parameters: parser The FTPFileEntryParser
that should be
used to parse each server file listing.
Returns: An iteratable object that holds the raw information and is
capable of providing parsed FTPFile objects, one for each file containing
information contained in the given path in the format determined by the
parser
parameter. Null will be returned if a
data connection cannot be opened. If the current working directory
contains no files, an empty array will be the return.
FTPClient f=FTPClient();
f.connect(server);
f.login(username, password);
FTPFileList list = f.createFileList(directory, parser);
FTPFileIterator iter = list.iterator();
while (iter.hasNext()) {
FTPFile[] files = iter.getNext(25); // "page size" you want
//do whatever you want with these files, display them, etc.
//expensive FTPFile objects not created until needed.
}
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
See Also: FTPFileList
Deprecated: - use initiateListParsing(String, FTPFileEntryParser) method instead.
Using a programmer specified FTPFileEntryParser
,
initialize an object containing a raw file information for a directory
or information for a single file. This information is obtained through
the LIST command. This object is then capable of being iterated to
return a sequence of FTPFile objects with information filled in by the
FTPFileEntryParser
used.
The server may or may not expand glob expressions. You should avoid
using glob expressions because the return format for glob listings
differs from server to server and will likely cause this method to fail.
Parameters: parser The FTPFileEntryParser
that should be
used to parse each server file listing. pathname The file or directory to list.
Returns: An iteratable object that holds the raw information and is
capable of providing parsed FTPFile objects, one for each file containing
information contained in the given path in the format determined by the
parser
parameter. Null will be returned if a
data connection cannot be opened. If the supplied path contains
no files, an empty array will be the return.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
See Also: FTPFileList
Parameters: pathname The pathname of the file to be deleted.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Throws: IOException If an error occurs while disconnecting.
ACTIVE_LOCAL_DATA_CONNECTION_MODE
. No communication
with the FTP server is conducted, but this causes all future data
transfers to require the FTP server to connect to the client's
data port. Additionally, to accommodate differences between socket
implementations on different platforms, this method causes the
client to issue a PORT command before every data transfer.
PASSIVE_LOCAL_DATA_CONNECTION_MODE
. Use this
method only for data transfers between the client and server.
This method causes a PASV command to be issued to the server
before the opening of every data connection, telling the server to
open a data port to which the client will connect to conduct
data transfers. The FTPClient will stay in
PASSIVE_LOCAL_DATA_CONNECTION_MODE
until the
mode is changed by calling some other method such as
{@link #enterLocalActiveMode enterLocalActiveMode() }
ACTIVE_REMOTE_DATA_CONNECTION
. Use this method only
for server to server data transfers. This method issues a PORT
command to the server, indicating the other server and port to which
it should connect for data transfers. You must call this method
before EVERY server to server transfer attempt. The FTPClient will
NOT automatically continue to issue PORT commands. You also
must remember to call
{@link #enterLocalActiveMode enterLocalActiveMode() } if you
wish to return to the normal data connection mode.
Parameters: host The passive mode server accepting connections for data transfers. port The passive mode server's data port.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
PASSIVE_REMOTE_DATA_CONNECTION_MODE
. Use this
method only for server to server data transfers.
This method issues a PASV command to the server, telling it to
open a data port to which the active server will connect to conduct
data transfers. You must call this method
before EVERY server to server transfer attempt. The FTPClient will
NOT automatically continue to issue PASV commands. You also
must remember to call
{@link #enterLocalActiveMode enterLocalActiveMode() } if you
wish to return to the normal data connection mode.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: The current buffer size.
_DATA_CONNECTION_MODE
constants.
Returns: The current data connection mode (one of the
_DATA_CONNECTION_MODE
constants.
Returns: The passive host name if in passive mode, otherwise null.
Returns: The data port of the passive server. If not in passive mode, undefined.
Returns: offset The offset into the remote file at which to start the next file transfer.
Returns: The status information returned by the server.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: The status information returned by the server.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: The system type name obtained from the server. null if the information could not be obtained.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
FTPFileEntryParser
used.
This method differs from using the listFiles() methods in that expensive FTPFile objects are not created until needed which may be an advantage on large lists.
Returns: A FTPListParseEngine object that holds the raw information and
is capable of providing parsed FTPFile objects, one for each file
containing information contained in the given path in the format
determined by the parser
parameter. Null will be
returned if a data connection cannot be opened. If the current working
directory contains no files, an empty array will be the return.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. ParserInitializationException Thrown if the autodetect mechanism cannot resolve the type of system we are connected with.
See Also: FTPListParseEngine
FTPFileEntryParser
used.
The server may or may not expand glob expressions. You should avoid using glob expressions because the return format for glob listings differs from server to server and will likely cause this method to fail.
This method differs from using the listFiles() methods in that expensive FTPFile objects are not created until needed which may be an advantage on large lists.
FTPClient f=FTPClient(); f.connect(server); f.login(username, password); FTPListParseEngine engine = f.initiateListParsing(directory); while (engine.hasNext()) { FTPFile[] files = engine.getNext(25); // "page size" you want //do whatever you want with these files, display them, etc. //expensive FTPFile objects not created until needed. }
Returns: A FTPListParseEngine object that holds the raw information and
is capable of providing parsed FTPFile objects, one for each file
containing information contained in the given path in the format
determined by the parser
parameter. Null will be
returned if a data connection cannot be opened. If the current working
directory contains no files, an empty array will be the return.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. ParserInitializationException Thrown if the autodetect mechanism cannot resolve the type of system we are connected with.
See Also: FTPListParseEngine
FTPFileEntryParser
used.
The server may or may not expand glob expressions. You should avoid using glob expressions because the return format for glob listings differs from server to server and will likely cause this method to fail.
This method differs from using the listFiles() methods in that expensive FTPFile objects are not created until needed which may be an advantage on large lists.
Parameters: parserKey A string representing a designated code or fully-qualified
class name of an FTPFileEntryParser
that should be
used to parse each server file listing.
Returns: A FTPListParseEngine object that holds the raw information and
is capable of providing parsed FTPFile objects, one for each file
containing information contained in the given path in the format
determined by the parser
parameter. Null will be
returned if a data connection cannot be opened. If the current working
directory contains no files, an empty array will be the return.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. ParserInitializationException Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
See Also: FTPListParseEngine
Returns: True if verification is enabled, false if not.
Deprecated: use {@link #listFiles() listFiles()} or {@link #listFiles(String) listFiles(String)} instead and specify the parser Key in an {@link #FTPClientConfig FTPClientConfig} object instead.
Using the suppliedparserKey
, obtain a list
of file information for the current working directory or for just a
single file.
If key
is null, this object will try to autodetect
the system-type/parser-type by calling the SYST command.
Under the DefaultFTPFileEntryParserFactory, which is used unless a different factory has been specified, the key can be either a recognized System type for which a parser has been defined, or the fully qualified class name of a class that implements org.apache.commons.net.ftp.FTPFileEntryParser.
This information is obtained through the LIST command. The contents of
the returned array is determined by the FTPFileEntryParser
used.
Parameters: parserKey This is a "handle" which the parser factory used
must be able to resolve into a class implementing
FTPFileEntryParser.
In the DefaultFTPFileEntryParserFactory, this
may either be a specific key identifying a server type,
which is used to identify a parser type,
or the fully qualified class name of the parser. See
DefaultFTPFileEntryParserFactory.createFileEntryParser
for full details.
If this parameter is null, will attempt to generate a key
by running the SYST command. This should cause no problem
with the functionality implemented in the
DefaultFTPFileEntryParserFactory, but may not map so well
to an alternative user-created factory. If that is the
case, calling this routine with a null parameter and a
custom parser factory may not be advisable.
Returns: The list of file information contained in the given path in
the format determined by the parser represented by the
NOTE: This array may contain null members if any of the
individual file listings failed to parse. The caller should
check each entry for null before referencing it. parserKey
parameter.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. ParserInitializationException Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
See Also: DefaultFTPFileEntryParserFactory FTPFileEntryParserFactory FTPFileEntryParser
This information is obtained through the LIST command. The contents of
the returned array is determined by the FTPFileEntryParser
used.
Parameters: pathname The file or directory to list. Since the server may or may not expand glob expressions, using them here is not recommended and may well cause this method to fail.
Returns: The list of file information contained in the given path in the format determined by the autodetection mechanism
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. ParserInitializationException Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
See Also: DefaultFTPFileEntryParserFactory FTPFileEntryParserFactory FTPFileEntryParser
This information is obtained through the LIST command. The contents of
the returned array is determined by the FTPFileEntryParser
used.
Returns: The list of file information contained in the current directory
in the format determined by the autodetection mechanism.
NOTE: This array may contain null members if any of the
individual file listings failed to parse. The caller should
check each entry for null before referencing it.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. ParserInitializationException Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
See Also: DefaultFTPFileEntryParserFactory FTPFileEntryParserFactory FTPFileEntryParser
Deprecated: use listFiles(String parserKey, String pathname) instead
Using a programmer specified FTPFileListParser
, obtain a
list of file information for a directory or information for
just a single file. This information is obtained through the LIST
command. The contents of the returned array is determined by the
FTPFileListParser
used.
The server may or may not expand glob expressions. You should avoid
using glob expressions because the return format for glob listings
differs from server to server and will likely cause this method to fail.
Parameters: parser The FTPFileListParser
that should be
used to parse the server file listing. pathname The file or directory to list.
Returns: The list of file information contained in the given path in
the format determined by the
NOTE: This array may contain null members if any of the
individual file listings failed to parse. The caller should
check each entry for null before referencing it.
NOTE: This array may contain null members if any of the
individual file listings failed to parse. The caller should
check each entry for null before referencing it.
parser
parameter.
parserKey
parameter.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. IOException
Since: 5 Jan 2004
Deprecated: use listFiles(String parserKey) instead.
Using a programmer specified FTPFileListParser
,
obtain a list of file information for the current working directory.
This information is obtained through the LIST command.
The contents of the array returned is determined by the
FTPFileListParser
used.
Parameters: parser The FTPFileListParser
that should be
used to parse the server file listing.
Returns: The list of file information contained in the given path in
the format determined by the
NOTE: This array may contain null members if any of the
individual file listings failed to parse. The caller should
check each entry for null before referencing it. parser
parameter.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server. IOException
Since: 5 Jan 2004
Returns: The system help string obtained from the server. null if the information could not be obtained.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: command The command on which to ask for help.
Returns: The command help string obtained from the server. null if the information could not be obtained.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: pathname The file or directory to list.
Returns: The list of filenames contained in the given path. null if the list could not be obtained. If there are no filenames in the directory, a zero-length array is returned.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: The list of filenames contained in the current working directory. null if the list could not be obtained. If there are no filenames in the directory, a zero-length array is returned.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: username The username to login under. password The password to use.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: username The username to login under. password The password to use. account The account to use.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: pathname The pathname of the directory to create.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: The pathname of the current working directory. If it cannot be obtained, returns null.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
remoteRetrieve
issued to it by another FTPClient.
Parameters: filename The name of the file to be appended to, or if the file does not exist, the name to call the file being stored.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: filename The name of the file to retrieve.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
remoteRetrieve
issued to it by another
FTPClient.
Parameters: filename The name to call the file that is to be stored.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
remoteRetrieve
issued
to it by another FTPClient.
Parameters: filename The name on which to base the filename of the file that is to be stored.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
remoteRetrieve
issued
to it by another FTPClient. Many FTP servers require that a base
filename be given from which the unique filename can be derived. For
those servers use the other version of remoteStoreUnique
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: pathname The pathname of the directory to remove.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: from The name of the remote file to rename. to The new name of the remote file.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: remote The name of the remote file. local The local OutputStream to which to write the file.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. CopyStreamException If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: remote The name of the remote file.
Returns: An InputStream from which the remote file can be read. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: arguments The site specific command and arguments.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: bufSize The size of the buffer
Parameters: timeout The default timeout in milliseconds that is used when opening a data connection socket.
FTP.FILE_STRUCTURE
if this method is never called.
Parameters: structure The structure of the file (one of the FTP class
_STRUCTURE
constants).
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
FTP.STREAM_TRANSFER_MODE
if this method is never called.
Parameters: mode The new transfer mode to use (one of the FTP class
_TRANSFER_MODE
constants).
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
FTP.ASCII_FILE_TYPE
, FTP.IMAGE_FILE_TYPE
,
etc. The file type only needs to be set when you want to change the
type. After changing it, the new type stays in effect until you change
it again. The default file type is FTP.ASCII_FILE_TYPE
if this method is never called.
Parameters: fileType The _FILE_TYPE
constant indcating the
type of file.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
FTP.ASCII_FILE_TYPE
,
FTP.IMAGE_FILE_TYPE
, etc. The file type only needs to
be set when you want to change the type. After changing it, the new
type stays in effect until you change it again. The default file type
is FTP.ASCII_FILE_TYPE
if this method is never called.
The format should be one of the FTP class TEXT_FORMAT
constants, or if the type is FTP.LOCAL_FILE_TYPE
, the
format should be the byte size for that type. The default format
is FTP.NON_PRINT_TEXT_FORMAT
if this method is never
called.
Parameters: fileType The _FILE_TYPE
constant indcating the
type of file. formatOrByteSize The format of the file (one of the
_FORMAT
constants. In the case of
LOCAL_FILE_TYPE
, the byte size.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: parserFactory factory object used to create FTPFileEntryParsers
See Also: FTPFileEntryParserFactory DefaultFTPFileEntryParserFactory
Parameters: enable True to enable verification, false to disable verification.
Parameters: offset The offset into the remote file at which to start the next file transfer. This must be a value greater than or equal to zero.
Parameters: remote The name to give the remote file. local The local InputStream from which to read the file.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. CopyStreamException If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: remote The name to give the remote file.
Returns: An OutputStream through which the remote file can be written. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: remote The name on which to base the unique name given to the remote file. local The local InputStream from which to read the file.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. CopyStreamException If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: local The local InputStream from which to read the file.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. CopyStreamException If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: remote The name on which to base the unique name given to the remote file.
Returns: An OutputStream through which the remote file can be written. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Returns: An OutputStream through which the remote file can be written. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: pathname The pathname to mount.
Returns: True if successfully completed, false if not.
Throws: FTPConnectionClosedException If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself. IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
Parameters: command The text representation of the FTP command to send. arg The arguments to the FTP command. If this parameter is set to null, then the command is sent with no argument.
Returns: A Socket corresponding to the established data connection. Null is returned if an FTP protocol error is reported at any point during the establishment and initialization of the connection.
Throws: IOException If an I/O error occurs while either sending a command to the server or receiving a reply from the server.