SocketClient
Date: 2016-06-23

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 java.lang.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 and Description
    --- | ---
    `protected int` | `_defaultPort_` The default port the client should connect to.
    `protected java.lang.String` | `_hostname_` The hostname used for the connection (null = no hostname supplied).
    `protected java.io.InputStream` | `_input_` The socket's InputStream.
    `protected java.io.OutputStream` | `_output_` The socket's OutputStream.
    `protected javax.net.ServerSocketFactory` | `_serverSocketFactory_` The socket's ServerSocket Factory.
    `protected java.net.Socket` | `_socket_` The socket used for the connection.
    `protected javax.net.SocketFactory` | `_socketFactory_` The socket's SocketFactory.
    `protected int` | `_timeout_` The timeout to use after opening a socket.
    `protected int` | `connectTimeout`
    `static java.lang.String` | `NETASCII_EOL` The end of line character sequence used by most IETF protocols.

  - ### Constructor Summary

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

  - ### Method Summary

    Methods
    Modifier and Type | Method and 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 of the connect() methods.
    `void` | `addProtocolCommandListener(ProtocolCommandListener listener)` Adds a ProtocolCommandListener.
    `void` | `connect(java.net.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(java.net.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(java.net.InetAddress host, int port, java.net.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(java.lang.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(java.lang.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(java.lang.String hostname, int port, java.net.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(java.lang.String command, java.lang.String message)` If there are any listeners, send them the command details.
    `protected void` | `fireReplyReceived(int replyCode, java.lang.String reply)` If there are any listeners, send them the reply details.
    `java.nio.charset.Charset` | `getCharset()` Gets the charset.
    `java.lang.String` | `getCharsetName()` Gets the charset name.
    `protected ProtocolCommandSupport` | `getCommandSupport()` Subclasses can override this if they need to provide their own instance field for backwards compatibilty.
    `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.
    `java.net.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.
    `java.net.Proxy` | `getProxy()` Gets the proxy for use with all the connections.
    `protected int` | `getReceiveBufferSize()` Get the current receivedBuffer size
    `java.net.InetAddress` | `getRemoteAddress()`
    `int` | `getRemotePort()` Returns the port number of the remote host to which the client is connected.
    `protected int` | `getSendBufferSize()` Get the current sendBuffer size
    `javax.net.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(java.nio.charset.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(java.net.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(javax.net.ServerSocketFactory factory)` Sets the ServerSocketFactory used by the SocketClient to open ServerSocket connections.
    `void` | `setSocketFactory(javax.net.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(java.net.Socket socket)` Verifies that the remote end of the given socket is connected to the 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 Detail

    - #### NETASCII_EOL

          public static final java.lang.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 java.net.Socket _socket_

      The socket used for the connection.

    - #### _hostname_

          protected java.lang.String _hostname_

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

    - #### _defaultPort_

          protected int _defaultPort_

      The default port the client should connect to.

    - #### _input_

          protected java.io.InputStream _input_

      The socket's InputStream.

    - #### _output_

          protected java.io.OutputStream _output_

      The socket's OutputStream.

    - #### _socketFactory_

          protected javax.net.SocketFactory _socketFactory_

      The socket's SocketFactory.

    - #### _serverSocketFactory_

          protected javax.net.ServerSocketFactory _serverSocketFactory_

      The socket's ServerSocket Factory.

    - #### connectTimeout

          protected int connectTimeout

  - ### Constructor Detail

    - #### 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 Detail

    - #### _connectAction_

          protected void _connectAction_()
                                  throws java.io.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 of 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:
        `java.io.IOException` - (SocketException) if a problem occurs with the socket

    - #### connect

          public void connect(java.net.InetAddress host,
                     int port)
                       throws java.net.SocketException,
                              java.io.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:
        `java.net.SocketException` - If the socket timeout could not be set.
        `java.io.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(java.lang.String hostname,
                     int port)
                       throws java.net.SocketException,
                              java.io.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:
        `java.net.SocketException` - If the socket timeout could not be set.
        `java.io.IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
        `java.net.UnknownHostException` - If the hostname cannot be resolved.

    - #### connect

          public void connect(java.net.InetAddress host,
                     int port,
                     java.net.InetAddress localAddr,
                     int localPort)
                       throws java.net.SocketException,
                              java.io.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:
        `java.net.SocketException` - If the socket timeout could not be set.
        `java.io.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(java.lang.String hostname,
                     int port,
                     java.net.InetAddress localAddr,
                     int localPort)
                       throws java.net.SocketException,
                              java.io.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:
        `java.net.SocketException` - If the socket timeout could not be set.
        `java.io.IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
        `java.net.UnknownHostException` - If the hostname cannot be resolved.

    - #### connect

          public void connect(java.net.InetAddress host)
                       throws java.net.SocketException,
                              java.io.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:
        `java.net.SocketException` - If the socket timeout could not be set.
        `java.io.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(java.lang.String hostname)
                       throws java.net.SocketException,
                              java.io.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:
        `java.net.SocketException` - If the socket timeout could not be set.
        `java.io.IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
        `java.net.UnknownHostException` - If the hostname cannot be resolved.

    - #### disconnect

          public void disconnect()
                          throws java.io.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:
        `java.io.IOException` - If there is an error closing the socket.

    - #### 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.

    - #### 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

    - #### 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.

    - #### getDefaultPort

          public int getDefaultPort()

      Returns the current value of the default port (stored in `_defaultPort_` ).

      Returns:
        The current value of the default port.

    - #### 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 an the currently opened socket. _timeout_ contains the new timeout value.

      Parameters:
        `timeout` - The timeout in milliseconds to use for the socket connection.

    - #### 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.

    - #### setSoTimeout

          public void setSoTimeout(int timeout)
                            throws java.net.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:
        `java.net.SocketException` - If the operation fails.
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### setSendBufferSize

          public void setSendBufferSize(int size)
                                 throws java.net.SocketException

      Set the underlying socket send buffer size.

      Parameters:
        `size` - The size of the buffer in bytes.
      Throws:
        `java.net.SocketException` - never thrown, but subclasses might want to do so
      Since:
        2.0

    - #### getSendBufferSize

          protected int getSendBufferSize()

      Get the current sendBuffer size
      Returns:
        the size, or -1 if not initialised
      Since:
        3.0

    - #### setReceiveBufferSize

          public void setReceiveBufferSize(int size)
                                    throws java.net.SocketException

      Sets the underlying socket receive buffer size.

      Parameters:
        `size` - The size of the buffer in bytes.
      Throws:
        `java.net.SocketException` - never (but subclasses may wish to do so)
      Since:
        2.0

    - #### getReceiveBufferSize

          protected int getReceiveBufferSize()

      Get the current receivedBuffer size
      Returns:
        the size, or -1 if not initialised
      Since:
        3.0

    - #### getSoTimeout

          public int getSoTimeout()
                           throws java.net.SocketException

      Returns the timeout in milliseconds of the currently opened socket.

      Returns:
        The timeout in milliseconds of the currently opened socket.
      Throws:
        `java.net.SocketException` - If the operation fails.
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### setTcpNoDelay

          public void setTcpNoDelay(boolean on)
                             throws java.net.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:
        `java.net.SocketException` - If the operation fails.
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### getTcpNoDelay

          public boolean getTcpNoDelay()
                                throws java.net.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:
        `java.net.SocketException` - If the operation fails.
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### setKeepAlive

          public void setKeepAlive(boolean keepAlive)
                            throws java.net.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:
        `java.net.SocketException` - if there is a problem with the socket
        `java.lang.NullPointerException` - if the socket is not currently open
      Since:
        2.2

    - #### getKeepAlive

          public boolean getKeepAlive()
                               throws java.net.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:
        `java.net.SocketException` - if there is a problem with the socket
        `java.lang.NullPointerException` - if the socket is not currently open
      Since:
        2.2

    - #### setSoLinger

          public void setSoLinger(boolean on,
                         int val)
                           throws java.net.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:
        `java.net.SocketException` - If the operation fails.
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### getSoLinger

          public int getSoLinger()
                          throws java.net.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:
        `java.net.SocketException` - If the operation fails.
        `java.lang.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:
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### getLocalAddress

          public java.net.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:
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### 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:
        `java.lang.NullPointerException` - if the socket is not currently open

    - #### getRemoteAddress

          public java.net.InetAddress getRemoteAddress()

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

    - #### verifyRemote

          public boolean verifyRemote(java.net.Socket socket)

      Verifies that the remote end of the given socket is connected to the 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.

    - #### setSocketFactory

          public void setSocketFactory(javax.net.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.

    - #### setServerSocketFactory

          public void setServerSocketFactory(javax.net.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

    - #### 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

    - #### getConnectTimeout

          public int getConnectTimeout()

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

    - #### getServerSocketFactory

          public javax.net.ServerSocketFactory getServerSocketFactory()

      Get the underlying `ServerSocketFactory`
      Returns:
        The server socket factory
      Since:
        2.2

    - #### addProtocolCommandListener

          public void addProtocolCommandListener(ProtocolCommandListener listener)

      Adds a ProtocolCommandListener.
      Parameters:
        `listener` - The ProtocolCommandListener to add.
      Since:
        3.0

    - #### removeProtocolCommandListener

          public void removeProtocolCommandListener(ProtocolCommandListener listener)

      Removes a ProtocolCommandListener.
      Parameters:
        `listener` - The ProtocolCommandListener to remove.
      Since:
        3.0

    - #### fireReplyReceived

          protected void fireReplyReceived(int replyCode,
                               java.lang.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

    - #### fireCommandSent

          protected void fireCommandSent(java.lang.String command,
                             java.lang.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

    - #### createCommandSupport

          protected void createCommandSupport()

      Create the CommandSupport instance if required

    - #### getCommandSupport

          protected ProtocolCommandSupport getCommandSupport()

      Subclasses can override this if they need to provide their own instance field for backwards compatibilty.
      Returns:
        the CommandSupport instance, may be `null`
      Since:
        3.0

    - #### setProxy

          public void setProxy(java.net.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

    - #### getProxy

          public java.net.Proxy getProxy()

      Gets the proxy for use with all the connections.
      Returns:
        the current proxy for connections.

    - #### getCharsetName

          public java.lang.String getCharsetName()

      Gets the charset name.
      Returns:
        the charset.
      Since:
        3.3 TODO Will be deprecated once the code requires Java 1.6 as a mininmum

    - #### getCharset

          public java.nio.charset.Charset getCharset()

      Gets the charset.
      Returns:
        the charset.
      Since:
        3.3

    - #### setCharset

          public void setCharset(java.nio.charset.Charset charset)

      Sets the charset.
      Parameters:
        `charset` - the charset.
      Since:
        3.3