# Class CardChannel

java.lang.Object
javax.smartcardio.CardChannel

public abstract class CardChannel extends Object
A logical channel connection to a Smart Card. It is used to exchange APDUs with a Smart Card. A CardChannel object can be obtained by calling the method Card.getBasicChannel() or Card.openLogicalChannel().

Since:
  1.6
See Also:
  - `Card`
  - `CommandAPDU`
  - `ResponseAPDU`

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `CardChannel()`
  Constructs a new CardChannel object.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract void`
  `close()`
  Closes this CardChannel.
  `abstract Card`
  `getCard()`
  Returns the Card this channel is associated with.
  `abstract int`
  `getChannelNumber()`
  Returns the channel number of this CardChannel.
  `abstract int`
  `transmit(ByteBuffer command, ByteBuffer response)`
  Transmits the command APDU stored in the command ByteBuffer and receives the response APDU in the response ByteBuffer.
  `abstract ResponseAPDU`
  `transmit(CommandAPDU command)`
  Transmits the specified command APDU to the Smart Card and returns the response APDU.

  ### Methods declared in class Object

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

- ## Constructor Details

  - ### CardChannel

    protected CardChannel()
    Constructs a new CardChannel object.

    This constructor is called by subclasses only. Application should call the Card.getBasicChannel() and Card.openLogicalChannel() methods to obtain a CardChannel object.

- ## Method Details

  - ### getCard

    public abstract Card getCard()
    Returns the Card this channel is associated with.
    Returns:
      the Card this channel is associated with

  - ### getChannelNumber

    public abstract int getChannelNumber()
    Returns the channel number of this CardChannel. A channel number of 0 indicates the basic logical channel.
    Returns:
      the channel number of this CardChannel.
    Throws:
      `IllegalStateException` - if this channel has been closed or if the corresponding Card has been disconnected.

  - ### transmit

    public abstract ResponseAPDU transmit(CommandAPDU command) throws CardException
    Transmits the specified command APDU to the Smart Card and returns the response APDU.

    The CLA byte of the command APDU is automatically adjusted to match the channel number of this CardChannel.

    Note that this method cannot be used to transmit `MANAGE CHANNEL` APDUs. Logical channels should be managed using the Card.openLogicalChannel() and CardChannel.close() methods.

    Implementations should transparently handle artifacts of the transmission protocol. For example, when using the T=0 protocol, the following processing should occur as described in ISO/IEC 7816-4:

    - if the response APDU has an SW1 of `61`, the implementation should issue a `GET RESPONSE` command using `SW2` as the `Le`field. This process is repeated as long as an SW1 of `61` is received. The response body of these exchanges is concatenated to form the final response body.

    - if the response APDU is `6C XX`, the implementation should reissue the command using `XX` as the `Le` field.

    The ResponseAPDU returned by this method is the result after this processing has been performed.

    Parameters:
      `command` - the command APDU
    Returns:
      the response APDU received from the card
    Throws:
      `IllegalStateException` - if this channel has been closed or if the corresponding Card has been disconnected.
      `IllegalArgumentException` - if the APDU encodes a `MANAGE CHANNEL` command
      `NullPointerException` - if command is null
      `CardException` - if the card operation failed

  - ### transmit

    public abstract int transmit(ByteBuffer command, ByteBuffer response) throws CardException
    Transmits the command APDU stored in the command ByteBuffer and receives the response APDU in the response ByteBuffer.

    The command buffer must contain valid command APDU data starting at `command.position()` and the APDU must be `command.remaining()` bytes long. Upon return, the command buffer's position will be equal to its limit; its limit will not have changed. The output buffer will have received the response APDU bytes. Its position will have advanced by the number of bytes received, which is also the return value of this method.

    The CLA byte of the command APDU is automatically adjusted to match the channel number of this CardChannel.

    Note that this method cannot be used to transmit `MANAGE CHANNEL` APDUs. Logical channels should be managed using the Card.openLogicalChannel() and CardChannel.close() methods.

    See transmit() for a discussion of the handling of response APDUs with the SW1 values `61` or `6C`.

    Parameters:
      `command` - the buffer containing the command APDU
      `response` - the buffer that shall receive the response APDU from the card
    Returns:
      the length of the received response APDU
    Throws:
      `IllegalStateException` - if this channel has been closed or if the corresponding Card has been disconnected.
      `NullPointerException` - if command or response is null
      `ReadOnlyBufferException` - if the response buffer is read-only
      `IllegalArgumentException` - if command and response are the same object, if `response` may not have sufficient space to receive the response APDU or if the APDU encodes a `MANAGE CHANNEL` command
      `CardException` - if the card operation failed

  - ### close

    public abstract void close() throws CardException
    Closes this CardChannel. The logical channel is closed by issuing a `MANAGE CHANNEL` command that should use the format `[xx 70 80 0n]` where `n` is the channel number of this channel and `xx` is the `CLA` byte that encodes this logical channel and has all other bits set to 0. After this method returns, calling other methods in this class will raise an IllegalStateException.

    Note that the basic logical channel cannot be closed using this method. It can be closed by calling `Card.disconnect(boolean)`.

    Throws:
      `CardException` - if the card operation failed
      `IllegalStateException` - if this CardChannel represents a connection the basic logical channel