What's use of inheritedChannel() method in System class [closed]

Question

Found this method in System class. Just curious to know about it-

public static Channel inheritedChannel() throws IOException {
     return SelectorProvider.provider().inheritedChannel();
}

Java Doc description is :

Returns the channel inherited from the entity that created this Java virtual machine. This method returns the channel obtained by invoking the inheritedChannel method of the system-wide default SelectorProvider object.

Answer 1

It’s designed for Java programs to be started on demand from inetd or xinetd on Unixy systems. Oracle has some more documentation and example code, unfortunately related to RMI, in their Designing Services to be Launched from inetd article, and there’s a very simple example in the Jetty source for InheritedChannelConnector and some interesting discussions in bug JETTY-496 where the Jetty feature was introduced.

Answer 2

From SelectorProvider.inheritedChannel():

Returns the channel inherited from the entity that created this Java virtual machine.

On many operating systems a process, such as a Java virtual machine, can be started in a manner that allows the process to inherit a channel from the entity that created the process. The manner in which this is done is system dependent, as are the possible entities to which the channel may be connected. For example, on UNIX systems, the Internet services daemon (inetd) is used to start programs to service requests when a request arrives on an associated network port. In this example, the process that is started, inherits a channel representing a network socket.

In cases where the inherited channel represents a network socket then the java.nio.channels.Channel type returned by this method is determined as follows:

• If the inherited channel represents a stream-oriented connected socket then a java.nio.channels.SocketChannel is returned. The socket channel is, at least initially, in blocking mode, bound to a socket address, and connected to a peer.

• If the inherited channel represents a stream-oriented listening socket then a java.nio.channels.ServerSocketChannel is returned. The server-socket channel is, at least initially, in blocking mode, and bound to a socket address.

• If the inherited channel is a datagram-oriented socket then a java.nio.channels.DatagramChannel is returned. The datagram channel is, at least initially, in blocking mode, and bound to a socket address.

In addition to the network-oriented channels described, this method may return other kinds of channels in the future.

The first invocation of this method creates the channel that is returned. Subsequent invocations of this method return the same channel.