Java Reference
In-Depth Information
Both methods throw a
SocketException
if the underlying socket implementation does
not recognize the SO_RCVBUF option. This might happen on a non-POSIX operating
system. The
setReceiveBufferSize()
method will throw an
IllegalArgumentExcep
tion
if its argument is less than or equal to zero.
SO_SNDBUF
DatagramSocket
has methods to get and set the suggested send buffer size used for
network output:
public
void
setSendBufferSize
(
int
size
)
throws
SocketException
public
int
getSendBufferSize
()
throws
SocketException
The
setSendBufferSize()
method suggests a number of bytes to use for buffering
output on this socket. Once again, however, the operating system is free to ignore this
suggestion. Consequently, you'll want to check the result of
setSendBufferSize()
by
immediately following it with a call to
getSendBufferSize()
to find out the real buffer
size.
Both methods throw a
SocketException
if the underlying native network software
doesn't understand the SO_SNDBUF option. The
setSendBufferSize()
method also
throws an
IllegalArgumentException
if its argument is less than or equal to zero.
SO_REUSEADDR
The SO_REUSEADDR option does not mean the same thing for UDP sockets as it does
for TCP sockets. For UDP, SO_REUSEADDR controls whether multiple datagram
sockets can bind to the same port and address
at the same time
. If multiple sockets are
bound to the same port, received packets will be copied to all bound sockets. This option
is controlled by these two methods:
public
void
setReuseAddress
(
boolean
on
)
throws
SocketException
public
boolean
getReuseAddress
()
throws
SocketException
For this to work reliably,
setReuseAddress()
must be called
before
the new socket binds
to the port. This means the socket must be created in an unconnected state using the
protected constructor that takes a
DatagramImpl
as an argument. In other words, it
won't work with a plain vanilla
DatagramSocket
. Reusable ports are most commonly
used for multicast sockets, which will be discussed in the next chapter. Datagram chan‐
nels also create unconnected datagram sockets that can be configured to reuse ports, as
you'll see later in this chapter.
SO_BROADCAST
The SO_BROADCAST option controls whether a socket is allowed to send packets to
and receive packets from broadcast addresses such as 192.168.254.255, the local network
