A membership key may represent a membership to receive all datagrams sent + * to the group, or it may be source-specific, meaning that it + * represents a membership that receives only datagrams from a specific source + * address. Whether or not a membership key is source-specific may be determined + * by invoking its {@link #getSourceAddress() getSourceAddress} method. + * + *
A membership key is valid upon creation and remains valid until the + * membership is dropped by invoking the {@link #drop() drop} method, or + * the channel is closed. The validity of the membership key may be tested + * by invoking its {@link #isValid() isValid} method. + * + *
Where a membership key is not source-specific and the underlying operation + * system supports source filtering, then the {@link #block block} and {@link + * #unblock unblock} methods can be used to block or unblock multicast datagrams + * from particular source addresses. + * + * @see MulticastChannel + * + * @since 1.7 + */ +public abstract class MembershipKey { + + /** + * Initializes a new instance of this class. + */ + protected MembershipKey() { + } + + /** + * Tells whether or not this membership is valid. + * + *
A multicast group membership is valid upon creation and remains + * valid until the membership is dropped by invoking the {@link #drop() drop} + * method, or the channel is closed. + * + * @return {@code true} if this membership key is valid, {@code false} + * otherwise + */ + public abstract boolean isValid(); + + /** + * Drop membership. + * + *
If the membership key represents a membership to receive all datagrams + * then the membership is dropped and the channel will no longer receive any + * datagrams sent to the group. If the membership key is source-specific + * then the channel will no longer receive datagrams sent to the group from + * that source address. + * + *
After membership is dropped it may still be possible to receive + * datagrams sent to the group. This can arise when datagrams are waiting to + * be received in the socket's receive buffer. After membership is dropped + * then the channel may {@link MulticastChannel#join join} the group again + * in which case a new membership key is returned. + * + *
Upon return, this membership object will be {@link #isValid() invalid}. + * If the multicast group membership is already invalid then invoking this + * method has no effect. Once a multicast group membership is invalid, + * it remains invalid forever. + * + * @throws IOException + * If an I/O error occurs + */ + public abstract void drop() throws IOException; + + /** + * Block multicast datagrams from the given source address. + * + *
If this membership key is not source-specific, and the underlying + * operating system supports source filtering, then this method blocks + * multicast datagrams from the given source address. If the given source + * address is already blocked then this method has no effect. + * After a source address is blocked it may still be possible to receive + * datagams from that source. This can arise when datagrams are waiting to + * be received in the socket's receive buffer. + * + * @param source + * The source address to block + * + * @return This membership key + * + * @throws IllegalArgumentException + * If the {@code source} parameter is not a unicast address or + * is not the same address type as the multicast group + * @throws IllegalStateException + * If this membership key is source-specific or is no longer valid + * @throws UnsupportedOperationException + * If the underlying operating system does not support source + * filtering + * @throws IOException + * If an I/O error occurs + */ + public abstract MembershipKey block(InetAddress source) throws IOException; + + /** + * Unblock multicast datagrams from the given source address that was + * previously blocked using the {@link #block(InetAddress) block} method. + * + * @param source + * The source address to unblock + * + * @return This membership key + * + * @throws IllegalStateException + * If the given source address is not currently blocked or the + * membership key is no longer valid + * @throws IOException + * If an I/O error occurs + */ + public abstract MembershipKey unblock(InetAddress source) throws IOException; + + /** + * Returns the channel for which this membership key was created. This + * method will continue to return the channel even after the membership + * becomes {@link #isValid invalid}. + * + * @return the channel + */ + public abstract MulticastChannel getChannel(); + + /** + * Returns the multicast group for which this membership key was created. + * This method will continue to return the group even after the membership + * becomes {@link #isValid invalid}. + * + * @return the multicast group + */ + public abstract InetAddress getGroup(); + + /** + * Returns the network interface for which this membership key was created. + * This method will continue to return the network interface even after the + * membership becomes {@link #isValid invalid}. + * + * @return the network interface + */ + public abstract NetworkInterface getNetworkInterface(); + + /** + * Returns the source address if this membership key is source-specific, + * or {@code null} if this membership is not source-specific. + * + * @return The source address if this membership key is source-specific, + * otherwise {@code null} + */ + public abstract InetAddress getSourceAddress(); +}