Package org.apache.commons.net

# Class SocketClient

java.lang.Object
org.apache.commons.net.SocketClient

Direct Known Subclasses:
  `CharGenTCPClient`, `DaytimeTCPClient`, `DiscardTCPClient`, `FingerClient`, `FTP`, `IMAP`, `NNTP`, `POP3`, `RExecClient`, `SMTP`, `TelnetClient`, `TimeTCPClient`

public abstract class SocketClient extends Object
The SocketClient provides the basic operations that are required of client objects accessing sockets. It is meant to be subclassed to avoid having to rewrite the same code over and over again to open a socket, close a socket, set timeouts, etc. Of special note is the `setSocketFactory` method, which allows you to control the type of Socket the SocketClient creates for initiating network connections. This is especially useful for adding SSL or proxy support as well as better support for applets. For example, you could create a `SocketFactory` that requests browser security capabilities before creating a socket. All classes derived from SocketClient should use the `_socketFactory_` member variable to create Socket and ServerSocket instances rather than instantiating them by directly invoking a constructor. By honoring this contract you guarantee that a user will always be able to provide his own Socket implementations by substituting his own SocketFactory.

See Also:
  - `SocketFactory`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected int`
  `_defaultPort_`
  The default port the client should connect to.
  `protected String`
  `_hostname_`
  The hostname used for the connection (null = no hostname supplied).
  `protected InputStream`
  `_input_`
  The socket's InputStream.
  `protected OutputStream`
  `_output_`
  The socket's OutputStream.
  `protected ServerSocketFactory`
  `_serverSocketFactory_`
  The socket's ServerSocket Factory.
  `protected Socket`
  `_socket_`
  The socket used for the connection.
  `protected SocketFactory`
  `_socketFactory_`
  The socket's SocketFactory.
  `protected int`
  `_timeout_`
  The timeout to use after opening a socket.
  `protected int`
  `connectTimeout`
  `static final String`
  `NETASCII_EOL`
  The end of line character sequence used by most IETF protocols.
  `protected InetSocketAddress`
  `remoteInetSocketAddress`
  The remote socket address used for the connection.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `SocketClient()`
  Default constructor for SocketClient.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected void`
  `_connectAction_()`
  Because there are so many connect() methods, the _connectAction_() method is provided as a means of performing some action immediately after establishing a connection, rather than reimplementing all the connect() methods.
  `void`
  `addProtocolCommandListener(ProtocolCommandListener listener)`
  Adds a ProtocolCommandListener.
  `protected void`
  `applySocketAttributes()`
  Applies socket attributes.
  `void`
  `connect(String hostname)`
  Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port.
  `void`
  `connect(String hostname, int port)`
  Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port.
  `void`
  `connect(String hostname, int port, InetAddress localAddr, int localPort)`
  Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
  `void`
  `connect(InetAddress host)`
  Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port.
  `void`
  `connect(InetAddress host, int port)`
  Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port.
  `void`
  `connect(InetAddress host, int port, InetAddress localAddr, int localPort)`
  Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
  `protected void`
  `createCommandSupport()`
  Create the CommandSupport instance if required
  `void`
  `disconnect()`
  Disconnects the socket connection.
  `protected void`
  `fireCommandSent(String command, String message)`
  If there are any listeners, send them the command details.
  `protected void`
  `fireReplyReceived(int replyCode, String reply)`
  If there are any listeners, send them the reply details.
  `Charset`
  `getCharset()`
  Gets the charset.
  `String`
  `getCharsetName()`
  Deprecated.
  Since the code now requires Java 1.6 as a minimum
  `protected ProtocolCommandSupport`
  `getCommandSupport()`
  Subclasses can override this if they need to provide their own instance field for backwards compatibility.
  `int`
  `getConnectTimeout()`
  Get the underlying socket connection timeout.
  `int`
  `getDefaultPort()`
  Returns the current value of the default port (stored in `_defaultPort_`).
  `int`
  `getDefaultTimeout()`
  Returns the default timeout in milliseconds that is used when opening a socket.
  `boolean`
  `getKeepAlive()`
  Returns the current value of the SO_KEEPALIVE flag on the currently opened socket.
  `InetAddress`
  `getLocalAddress()`
  Returns the local address to which the client's socket is bound.
  `int`
  `getLocalPort()`
  Returns the port number of the open socket on the local host used for the connection.
  `Proxy`
  `getProxy()`
  Gets the proxy for use with all the connections.
  `protected int`
  `getReceiveBufferSize()`
  Get the current receivedBuffer size
  `InetAddress`
  `getRemoteAddress()`
  `protected InetSocketAddress`
  `getRemoteInetSocketAddress()`
  Gets the remote socket address used for the connection.
  `int`
  `getRemotePort()`
  Returns the port number of the remote host to which the client is connected.
  `protected int`
  `getSendBufferSize()`
  Get the current sendBuffer size
  `ServerSocketFactory`
  `getServerSocketFactory()`
  Get the underlying `ServerSocketFactory`
  `int`
  `getSoLinger()`
  Returns the current SO_LINGER timeout of the currently opened socket.
  `int`
  `getSoTimeout()`
  Returns the timeout in milliseconds of the currently opened socket.
  `boolean`
  `getTcpNoDelay()`
  Returns true if Nagle's algorithm is enabled on the currently opened socket.
  `boolean`
  `isAvailable()`
  Make various checks on the socket to test if it is available for use.
  `boolean`
  `isConnected()`
  Returns true if the client is currently connected to a server.
  `void`
  `removeProtocolCommandListener(ProtocolCommandListener listener)`
  Removes a ProtocolCommandListener.
  `void`
  `setCharset(Charset charset)`
  Sets the charset.
  `void`
  `setConnectTimeout(int connectTimeout)`
  Sets the connection timeout in milliseconds, which will be passed to the `Socket` object's connect() method.
  `void`
  `setDefaultPort(int port)`
  Sets the default port the SocketClient should connect to when a port is not specified.
  `void`
  `setDefaultTimeout(int timeout)`
  Set the default timeout in milliseconds to use when opening a socket.
  `void`
  `setKeepAlive(boolean keepAlive)`
  Sets the SO_KEEPALIVE flag on the currently opened socket.
  `void`
  `setProxy(Proxy proxy)`
  Sets the proxy for use with all the connections.
  `void`
  `setReceiveBufferSize(int size)`
  Sets the underlying socket receive buffer size.
  `void`
  `setSendBufferSize(int size)`
  Set the underlying socket send buffer size.
  `void`
  `setServerSocketFactory(ServerSocketFactory factory)`
  Sets the ServerSocketFactory used by the SocketClient to open ServerSocket connections.
  `void`
  `setSocketFactory(SocketFactory factory)`
  Sets the SocketFactory used by the SocketClient to open socket connections.
  `void`
  `setSoLinger(boolean on, int val)`
  Sets the SO_LINGER timeout on the currently opened socket.
  `void`
  `setSoTimeout(int timeout)`
  Set the timeout in milliseconds of a currently open connection.
  `void`
  `setTcpNoDelay(boolean on)`
  Enables or disables the Nagle's algorithm (TCP_NODELAY) on the currently opened socket.
  `boolean`
  `verifyRemote(Socket socket)`
  Verifies that the remote end of the given socket is connected to the same host that the SocketClient is currently connected to.

  ### Methods inherited from class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### NETASCII_EOL

    public static final String NETASCII_EOL
    The end of line character sequence used by most IETF protocols. That is a carriage return followed by a newline: "\r\n"
    See Also:
      - Constant Field Values

  - ### _timeout_

    protected int _timeout_
    The timeout to use after opening a socket.

  - ### _socket_

    protected Socket _socket_
    The socket used for the connection.

  - ### _hostname_

    protected String _hostname_
    The hostname used for the connection (null = no hostname supplied).

  - ### remoteInetSocketAddress

    protected InetSocketAddress remoteInetSocketAddress
    The remote socket address used for the connection.

  - ### _defaultPort_

    protected int _defaultPort_
    The default port the client should connect to.

  - ### _input_

    protected InputStream _input_
    The socket's InputStream.

  - ### _output_

    protected OutputStream _output_
    The socket's OutputStream.

  - ### _socketFactory_

    protected SocketFactory _socketFactory_
    The socket's SocketFactory.

  - ### _serverSocketFactory_

    protected ServerSocketFactory _serverSocketFactory_
    The socket's ServerSocket Factory.

  - ### connectTimeout

    protected int connectTimeout

- ## Constructor Details

  - ### SocketClient

    public SocketClient()
    Default constructor for SocketClient. Initializes _socket_ to null, _timeout_ to 0, _defaultPort to 0, _isConnected_ to false, charset to `Charset.defaultCharset()` and _socketFactory_ to a shared instance of `DefaultSocketFactory`.

- ## Method Details

  - ### _connectAction_

    protected void _connectAction_() throws IOException
    Because there are so many connect() methods, the _connectAction_() method is provided as a means of performing some action immediately after establishing a connection, rather than reimplementing all the connect() methods. The last action performed by every connect() method after opening a socket is to call this method.

    This method sets the timeout on the just opened socket to the default timeout set by `setDefaultTimeout()` , sets _input_ and _output_ to the socket's InputStream and OutputStream respectively, and sets _isConnected_ to true.

    Subclasses overriding this method should start by calling `super._connectAction_()` first to ensure the initialization of the aforementioned protected variables.

    Throws:
      `IOException` - (SocketException) if a problem occurs with the socket

  - ### addProtocolCommandListener

    public void addProtocolCommandListener(ProtocolCommandListener listener)
    Adds a ProtocolCommandListener.
    Parameters:
      `listener` - The ProtocolCommandListener to add.
    Since:
      3.0

  - ### applySocketAttributes

    protected void applySocketAttributes() throws SocketException
    Applies socket attributes.
    Throws:
      `SocketException` - if there is an error in the underlying protocol, such as a TCP error.
    Since:
      3.8.0

  - ### connect

    public void connect(InetAddress host) throws SocketException, IOException
    Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.
    Parameters:
      `host` - The remote host.
    Throws:
      `SocketException` - If the socket timeout could not be set.
      `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

  - ### connect

    public void connect(InetAddress host, int port) throws SocketException, IOException
    Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.
    Parameters:
      `host` - The remote host.
      `port` - The port to connect to on the remote host.
    Throws:
      `SocketException` - If the socket timeout could not be set.
      `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

  - ### connect

    public void connect(InetAddress host, int port, InetAddress localAddr, int localPort) throws SocketException, IOException
    Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. Before returning, `_connectAction_()` is called to perform connection initialization actions.
    Parameters:
      `host` - The remote host.
      `port` - The port to connect to on the remote host.
      `localAddr` - The local address to use.
      `localPort` - The local port to use.
    Throws:
      `SocketException` - If the socket timeout could not be set.
      `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

  - ### connect

    public void connect(String hostname) throws SocketException, IOException
    Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.
    Parameters:
      `hostname` - The name of the remote host.
    Throws:
      `SocketException` - If the socket timeout could not be set.
      `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
      `UnknownHostException` - If the hostname cannot be resolved.

  - ### connect

    public void connect(String hostname, int port) throws SocketException, IOException
    Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.
    Parameters:
      `hostname` - The name of the remote host.
      `port` - The port to connect to on the remote host.
    Throws:
      `SocketException` - If the socket timeout could not be set.
      `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
      `UnknownHostException` - If the hostname cannot be resolved.

  - ### connect

    public void connect(String hostname, int port, InetAddress localAddr, int localPort) throws SocketException, IOException
    Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. Before returning, `_connectAction_()` is called to perform connection initialization actions.
    Parameters:
      `hostname` - The name of the remote host.
      `port` - The port to connect to on the remote host.
      `localAddr` - The local address to use.
      `localPort` - The local port to use.
    Throws:
      `SocketException` - If the socket timeout could not be set.
      `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
      `UnknownHostException` - If the hostname cannot be resolved.

  - ### createCommandSupport

    protected void createCommandSupport()
    Create the CommandSupport instance if required

  - ### disconnect

    public void disconnect() throws IOException
    Disconnects the socket connection. You should call this method after you've finished using the class instance and also before you call `connect()` again. _isConnected_ is set to false, _socket_ is set to null, _input_ is set to null, and _output_ is set to null.
    Throws:
      `IOException` - If there is an error closing the socket.

  - ### fireCommandSent

    protected void fireCommandSent(String command, String message)
    If there are any listeners, send them the command details.
    Parameters:
      `command` - the command name
      `message` - the complete message, including command name
    Since:
      3.0

  - ### fireReplyReceived

    protected void fireReplyReceived(int replyCode, String reply)
    If there are any listeners, send them the reply details.
    Parameters:
      `replyCode` - the code extracted from the reply
      `reply` - the full reply text
    Since:
      3.0

  - ### getCharset

    public Charset getCharset()
    Gets the charset.
    Returns:
      the charset.
    Since:
      3.3

  - ### getCharsetName

    @Deprecated public String getCharsetName()
    Deprecated.
    Since the code now requires Java 1.6 as a minimum
    Gets the charset name.
    Returns:
      the charset.
    Since:
      3.3

  - ### getCommandSupport

    protected ProtocolCommandSupport getCommandSupport()
    Subclasses can override this if they need to provide their own instance field for backwards compatibility.
    Returns:
      the CommandSupport instance, may be `null`
    Since:
      3.0

  - ### getConnectTimeout

    public int getConnectTimeout()
    Get the underlying socket connection timeout.
    Returns:
      timeout (in ms)
    Since:
      2.0

  - ### getDefaultPort

    public int getDefaultPort()
    Returns the current value of the default port (stored in `_defaultPort_` ).
    Returns:
      The current value of the default port.

  - ### getDefaultTimeout

    public int getDefaultTimeout()
    Returns the default timeout in milliseconds that is used when opening a socket.
    Returns:
      The default timeout in milliseconds that is used when opening a socket.

  - ### getKeepAlive

    public boolean getKeepAlive() throws SocketException
    Returns the current value of the SO_KEEPALIVE flag on the currently opened socket. Delegates to `Socket.getKeepAlive()`
    Returns:
      True if SO_KEEPALIVE is enabled.
    Throws:
      `SocketException` - if there is a problem with the socket
      `NullPointerException` - if the socket is not currently open
    Since:
      2.2

  - ### getLocalAddress

    public InetAddress getLocalAddress()
    Returns the local address to which the client's socket is bound. Delegates to `Socket.getLocalAddress()`
    Returns:
      The local address to which the client's socket is bound.
    Throws:
      `NullPointerException` - if the socket is not currently open

  - ### getLocalPort

    public int getLocalPort()
    Returns the port number of the open socket on the local host used for the connection. Delegates to `Socket.getLocalPort()`
    Returns:
      The port number of the open socket on the local host used for the connection.
    Throws:
      `NullPointerException` - if the socket is not currently open

  - ### getProxy

    public Proxy getProxy()
    Gets the proxy for use with all the connections.
    Returns:
      the current proxy for connections.

  - ### getReceiveBufferSize

    protected int getReceiveBufferSize()
    Get the current receivedBuffer size
    Returns:
      the size, or -1 if not initialized
    Since:
      3.0

  - ### getRemoteAddress

    public InetAddress getRemoteAddress()
    Returns:
      The remote address to which the client is connected. Delegates to `Socket.getInetAddress()`
    Throws:
      `NullPointerException` - if the socket is not currently open

  - ### getRemoteInetSocketAddress

    protected InetSocketAddress getRemoteInetSocketAddress()
    Gets the remote socket address used for the connection.
    Returns:
      the remote socket address used for the connection
    Since:
      3.10.0

  - ### getRemotePort

    public int getRemotePort()
    Returns the port number of the remote host to which the client is connected. Delegates to `Socket.getPort()`
    Returns:
      The port number of the remote host to which the client is connected.
    Throws:
      `NullPointerException` - if the socket is not currently open

  - ### getSendBufferSize

    protected int getSendBufferSize()
    Get the current sendBuffer size
    Returns:
      the size, or -1 if not initialized
    Since:
      3.0

  - ### getServerSocketFactory

    public ServerSocketFactory getServerSocketFactory()
    Get the underlying `ServerSocketFactory`
    Returns:
      The server socket factory
    Since:
      2.2

  - ### getSoLinger

    public int getSoLinger() throws SocketException
    Returns the current SO_LINGER timeout of the currently opened socket.
    Returns:
      The current SO_LINGER timeout. If SO_LINGER is disabled returns -1.
    Throws:
      `SocketException` - If the operation fails.
      `NullPointerException` - if the socket is not currently open

  - ### getSoTimeout

    public int getSoTimeout() throws SocketException
    Returns the timeout in milliseconds of the currently opened socket.
    Returns:
      The timeout in milliseconds of the currently opened socket.
    Throws:
      `SocketException` - If the operation fails.
      `NullPointerException` - if the socket is not currently open

  - ### getTcpNoDelay

    public boolean getTcpNoDelay() throws SocketException
    Returns true if Nagle's algorithm is enabled on the currently opened socket.
    Returns:
      True if Nagle's algorithm is enabled on the currently opened socket, false otherwise.
    Throws:
      `SocketException` - If the operation fails.
      `NullPointerException` - if the socket is not currently open

  - ### isAvailable

    public boolean isAvailable()
    Make various checks on the socket to test if it is available for use. Note that the only sure test is to use it, but these checks may help in some cases.
    Returns:
      `true` if the socket appears to be available for use
    Since:
      3.0
    See Also:
      - NET-350

  - ### isConnected

    public boolean isConnected()
    Returns true if the client is currently connected to a server. Delegates to `Socket.isConnected()`
    Returns:
      True if the client is currently connected to a server, false otherwise.

  - ### removeProtocolCommandListener

    public void removeProtocolCommandListener(ProtocolCommandListener listener)
    Removes a ProtocolCommandListener.
    Parameters:
      `listener` - The ProtocolCommandListener to remove.
    Since:
      3.0

  - ### setCharset

    public void setCharset(Charset charset)
    Sets the charset.
    Parameters:
      `charset` - the charset.
    Since:
      3.3

  - ### setConnectTimeout

    public void setConnectTimeout(int connectTimeout)
    Sets the connection timeout in milliseconds, which will be passed to the `Socket` object's connect() method.
    Parameters:
      `connectTimeout` - The connection timeout to use (in ms)
    Since:
      2.0

  - ### setDefaultPort

    public void setDefaultPort(int port)
    Sets the default port the SocketClient should connect to when a port is not specified. The `_defaultPort_` variable stores this value. If never set, the default port is equal to zero.
    Parameters:
      `port` - The default port to set.

  - ### setDefaultTimeout

    public void setDefaultTimeout(int timeout)
    Set the default timeout in milliseconds to use when opening a socket. This value is only used previous to a call to `connect()` and should not be confused with `setSoTimeout()` which operates on the currently opened socket. _timeout_ contains the new timeout value.
    Parameters:
      `timeout` - The timeout in milliseconds to use for the socket connection.

  - ### setKeepAlive

    public void setKeepAlive(boolean keepAlive) throws SocketException
    Sets the SO_KEEPALIVE flag on the currently opened socket. From the Javadocs, the default keepalive time is 2 hours (although this is implementation dependent). It looks as though the Windows WSA sockets implementation allows a specific keepalive value to be set, although this seems not to be the case on other systems.
    Parameters:
      `keepAlive` - If true, keepAlive is turned on
    Throws:
      `SocketException` - if there is a problem with the socket
      `NullPointerException` - if the socket is not currently open
    Since:
      2.2

  - ### setProxy

    public void setProxy(Proxy proxy)
    Sets the proxy for use with all the connections. The proxy is used for connections established after the call to this method.
    Parameters:
      `proxy` - the new proxy for connections.
    Since:
      3.2

  - ### setReceiveBufferSize

    public void setReceiveBufferSize(int size) throws SocketException
    Sets the underlying socket receive buffer size.
    Parameters:
      `size` - The size of the buffer in bytes.
    Throws:
      `SocketException` - never (but subclasses may wish to do so)
    Since:
      2.0

  - ### setSendBufferSize

    public void setSendBufferSize(int size) throws SocketException
    Set the underlying socket send buffer size.
    Parameters:
      `size` - The size of the buffer in bytes.
    Throws:
      `SocketException` - never thrown, but subclasses might want to do so
    Since:
      2.0

  - ### setServerSocketFactory

    public void setServerSocketFactory(ServerSocketFactory factory)
    Sets the ServerSocketFactory used by the SocketClient to open ServerSocket connections. If the factory value is null, then a default factory is used (only do this to reset the factory after having previously altered it).
    Parameters:
      `factory` - The new ServerSocketFactory the SocketClient should use.
    Since:
      2.0

  - ### setSocketFactory

    public void setSocketFactory(SocketFactory factory)
    Sets the SocketFactory used by the SocketClient to open socket connections. If the factory value is null, then a default factory is used (only do this to reset the factory after having previously altered it). Any proxy setting is discarded.
    Parameters:
      `factory` - The new SocketFactory the SocketClient should use.

  - ### setSoLinger

    public void setSoLinger(boolean on, int val) throws SocketException
    Sets the SO_LINGER timeout on the currently opened socket.
    Parameters:
      `on` - True if linger is to be enabled, false if not.
      `val` - The `linger` timeout (in hundredths of a second?)
    Throws:
      `SocketException` - If the operation fails.
      `NullPointerException` - if the socket is not currently open

  - ### setSoTimeout

    public void setSoTimeout(int timeout) throws SocketException
    Set the timeout in milliseconds of a currently open connection. Only call this method after a connection has been opened by `connect()`.

    To set the initial timeout, use `setDefaultTimeout(int)` instead.

    Parameters:
      `timeout` - The timeout in milliseconds to use for the currently open socket connection.
    Throws:
      `SocketException` - If the operation fails.
      `NullPointerException` - if the socket is not currently open

  - ### setTcpNoDelay

    public void setTcpNoDelay(boolean on) throws SocketException
    Enables or disables the Nagle's algorithm (TCP_NODELAY) on the currently opened socket.
    Parameters:
      `on` - True if Nagle's algorithm is to be enabled, false if not.
    Throws:
      `SocketException` - If the operation fails.
      `NullPointerException` - if the socket is not currently open

  - ### verifyRemote

    public boolean verifyRemote(Socket socket)
    Verifies that the remote end of the given socket is connected to the same host that the SocketClient is currently connected to. This is useful for doing a quick security check when a client needs to accept a connection from a server, such as an FTP data connection or a BSD R command standard error stream.
    Parameters:
      `socket` - the item to check against
    Returns:
      True if the remote hosts are the same, false if not.