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 instanting
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.
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"
_defaultPort_
protected int _defaultPort_
The default port the client should connect to.
_input_
protected InputStream _input_
The socket's InputStream.
_isConnected_
protected boolean _isConnected_
A status variable indicating if the client's socket is currently open.
_output_
protected OutputStream _output_
The socket's OutputStream.
_socketFactory_
protected SocketFactory _socketFactory_
The socket's SocketFactory.
_socket_
protected Socket _socket_
The socket used for the connection.
_timeout_
protected int _timeout_
The timeout to use after opening a socket.
_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
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.
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.
host
- The remote host.
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.
host
- The remote host.port
- The port to connect to on the remote host.
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.
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.
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.
hostname
- The name of the remote host.
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.
hostname
- The name of the remote host.port
- The port to connect to on the remote host.
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.
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.
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.
getDefaultPort
public int getDefaultPort()
Returns the current value of the default port (stored in
_defaultPort_
).
- The current value of the default port.
getDefaultTimeout
public int getDefaultTimeout()
Returns the default timeout in milliseconds that is used when
opening a socket.
- The default timeout in milliseconds that is used when
opening a socket.
getLocalAddress
public InetAddress getLocalAddress()
Returns the local address to which the client's socket is bound.
- The local address to which the client's socket is bound.
getLocalPort
public int getLocalPort()
Returns the port number of the open socket on the local host used
for the connection.
- The port number of the open socket on the local host used
for the connection.
getRemoteAddress
public InetAddress getRemoteAddress()
- The remote address to which the client is connected.
getRemotePort
public int getRemotePort()
Returns the port number of the remote host to which the client is
connected.
- The port number of the remote host to which the client is
connected.
getSoLinger
public int getSoLinger()
throws SocketException
Returns the current SO_LINGER timeout of the currently opened socket.
- The current SO_LINGER timeout. If SO_LINGER is disabled returns
-1.
getSoTimeout
public int getSoTimeout()
throws SocketException
Returns the timeout in milliseconds of the currently opened socket.
- The timeout in milliseconds of the currently opened socket.
getTcpNoDelay
public boolean getTcpNoDelay()
throws SocketException
Returns true if Nagle's algorithm is enabled on the currently opened
socket.
- True if Nagle's algorithm is enabled on the currently opened
socket, false otherwise.
isConnected
public boolean isConnected()
Returns true if the client is currently connected to a server.
- True if the client is currently connected to a server,
false otherwise.
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.
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 an the currently opened socket. _timeout_ contains
the new timeout value.
timeout
- The timeout in milliseconds to use for the socket
connection.
setSoLinger
public void setSoLinger(boolean on,
int val)
throws SocketException
Sets the SO_LINGER timeout on the currently opened socket.
on
- True if linger is to be enabled, false if not.val
- The linger timeout (in hundredths of a second?)
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()
.
timeout
- The timeout in milliseconds to use for the currently
open socket connection.
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).
factory
- The new SocketFactory the SocketClient should use.
setTcpNoDelay
public void setTcpNoDelay(boolean on)
throws SocketException
Enables or disables the Nagle's algorithm (TCP_NODELAY) on the
currently opened socket.
on
- True if Nagle's algorithm is to be enabled, false if not.
verifyRemote
public boolean verifyRemote(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.
- True if the remote hosts are the same, false if not.