UDP - Java Network Programming - page 440

Table 12-1. Socket options supported by datagram sockets
Option Type Constant Purpose

SO_SNDBUF Size of the buffer used for

sending datagram packets

StandardSocketOptions. Integer

SO_RCVBUF Size of the buffer used for

receiving datagram packets

StandardSocketOp
tions.SO_RCVBUF

Integer

SO_REUSEADDR Enable/disable address reuse

StandardSocketOptions.SO_RE
USEADDR

Boolean

SO_BROADCAST Enable/disable broadcast

messages

StandardSocketOp
tions.SO_BROADCAST

Boolean

IP_TOS Traffic class

StandardSocketOptions.IP_TOS Integer

IP_MULTICAST_IF Local network interface to use for

multicast

StandardSocketOptions.IP_MUL
TICAST_IF

NetworkInter
face

IP_MULTICAST_TTL Time-to-live value for multicast

datagrams

StandardSocketOptions.IP_MUL
TICAST_TTL

Integer

IP_MULTICAST_LOOP StandardSocketOptions.IP_MUL
TICAST_LOOP

Enable/disable loopback of
multicast datagrams

Boolean

The first five options have the same meanings as they do for datagram sockets as de‐
scribed in “Socket Options” on page 417 . The last three are used by multicast sockets,
which we'll take up in Chapter 13 .

These are inspected and configured by just three methods:

public <T> DatagramChannel setOption(SocketOption<T> name, T value)
throws IOException
public <T> T getOption(SocketOption<T> name) throws IOException
public Set<SocketOption<?>> supportedOptions()
The supportedOptions() method lists the available socket options. The getOption()
method tells you the current value of any of these. And setOption() lets you change
the value. For example, suppose you want to send a broadcast message. SO_BROAD‐
CAST is usually turned off by default, but you can switch it on like so:

try (DatagramChannel channel = DatagramChannel.open()) {
channel.setOption(StandardSocketOptions.SO_BROADCAST, true);
// Send the broadcast message...
} catch (IOException ex) {
// handle exceptions...
}
Example 12-18 opens a channel just to check the default values of these options.

Example 12-18. Default socket option values
import java.io.IOException ;
import java.net.SocketOption ;
import java.nio.channels.DatagramChannel ;