public class DatagramSocket extends Object implements Closeable
This class represents a socket for sending and receiving datagram packets.
A datagram socket is the sending or receiving point for a packet delivery service. Each packet sent or received on a datagram socket is individually addressed and routed. Multiple packets sent from one machine to another may be routed differently, and may arrive in any order.
Where possible, a newly constructed DatagramSocket
has the SO_BROADCAST
socket option enabled so as to allow the transmission of broadcast datagrams. In order to receive broadcast packets a DatagramSocket should be bound to the wildcard address. In some implementations, broadcast packets may also be received when a DatagramSocket is bound to a more specific address.
Example: DatagramSocket s = new DatagramSocket(null);
s.bind(new InetSocketAddress(8888));
Which is equivalent to: DatagramSocket s = new DatagramSocket(8888);
Both cases will create a DatagramSocket able to receive broadcasts on UDP port 8888.
DatagramPacket
, DatagramChannel
public DatagramSocket() throws SocketException
Constructs a datagram socket and binds it to any available port on the local host machine. The socket will be bound to the wildcard
address, an IP address chosen by the kernel.
If there is a security manager, its checkListen
method is first called with 0 as its argument to ensure the operation is allowed. This could result in a SecurityException.
SocketException
- if the socket could not be opened, or the socket could not bind to the specified local port.SecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
protected DatagramSocket(DatagramSocketImpl impl)
Creates an unbound datagram socket with the specified DatagramSocketImpl.
impl
- an instance of a DatagramSocketImpl the subclass wishes to use on the DatagramSocket.public DatagramSocket(SocketAddress bindaddr) throws SocketException
Creates a datagram socket, bound to the specified local socket address.
If, if the address is null
, creates an unbound socket.
If there is a security manager, its checkListen
method is first called with the port from the socket address as its argument to ensure the operation is allowed. This could result in a SecurityException.
bindaddr
- local socket address to bind, or null
for an unbound socket.SocketException
- if the socket could not be opened, or the socket could not bind to the specified local port.SecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
public DatagramSocket(int port) throws SocketException
Constructs a datagram socket and binds it to the specified port on the local host machine. The socket will be bound to the wildcard
address, an IP address chosen by the kernel.
If there is a security manager, its checkListen
method is first called with the port
argument as its argument to ensure the operation is allowed. This could result in a SecurityException.
port
- port to use.SocketException
- if the socket could not be opened, or the socket could not bind to the specified local port.SecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
public DatagramSocket(int port, InetAddress laddr) throws SocketException
Creates a datagram socket, bound to the specified local address. The local port must be between 0 and 65535 inclusive. If the IP address is 0.0.0.0, the socket will be bound to the wildcard
address, an IP address chosen by the kernel.
If there is a security manager, its checkListen
method is first called with the port
argument as its argument to ensure the operation is allowed. This could result in a SecurityException.
port
- local port to useladdr
- local address to bindSocketException
- if the socket could not be opened, or the socket could not bind to the specified local port.SecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.SecurityManager.checkListen(int)
public void bind(SocketAddress addr) throws SocketException
Binds this DatagramSocket to a specific address and port.
If the address is null
, then the system will pick up an ephemeral port and a valid local address to bind the socket.
addr
- The address and port to bind to.SocketException
- if any error happens during the bind, or if the socket is already bound.SecurityException
- if a security manager exists and its checkListen
method doesn't allow the operation.IllegalArgumentException
- if addr is a SocketAddress subclass not supported by this socket.public void connect(InetAddress address, int port)
Connects the socket to a remote address for this socket. When a socket is connected to a remote address, packets may only be sent to or received from that address. By default a datagram socket is not connected.
If the remote destination to which the socket is connected does not exist, or is otherwise unreachable, and if an ICMP destination unreachable packet has been received for that address, then a subsequent call to send or receive may throw a PortUnreachableException. Note, there is no guarantee that the exception will be thrown.
If a security manager has been installed then it is invoked to check access to the remote address. Specifically, if the given address
is a multicast address
, the security manager's checkMulticast
method is invoked with the given address
. Otherwise, the security manager's checkConnect
and checkAccept
methods are invoked, with the given address
and port
, to verify that datagrams are permitted to be sent and received respectively.
When a socket is connected, receive
and send
will not perform any security checks on incoming and outgoing packets, other than matching the packet's and the socket's address and port. On a send operation, if the packet's address is set and the packet's address and the socket's address do not match, an IllegalArgumentException
will be thrown. A socket connected to a multicast address may only be used to send packets.
address
- the remote address for the socketport
- the remote port for the socket.IllegalArgumentException
- if the address is null, or the port is out of range.SecurityException
- if a security manager has been installed and it does not permit access to the given remote addressdisconnect()
public void connect(SocketAddress addr) throws SocketException
Connects this socket to a remote socket address (IP address + port number).
If given an InetSocketAddress
, this method behaves as if invoking connect(InetAddress,int)
with the the given socket addresses IP address and port number.
addr
- The remote address.SocketException
- if the connect failsIllegalArgumentException
- if addr
is null
, or addr
is a SocketAddress subclass not supported by this socketSecurityException
- if a security manager has been installed and it does not permit access to the given remote addresspublic void disconnect()
Disconnects the socket. If the socket is closed or not connected, then this method has no effect.
connect(java.net.InetAddress, int)
public boolean isBound()
Returns the binding state of the socket.
If the socket was bound prior to being closed
, then this method will continue to return true
after the socket is closed.
public boolean isConnected()
Returns the connection state of the socket.
If the socket was connected prior to being closed
, then this method will continue to return true
after the socket is closed.
public InetAddress getInetAddress()
Returns the address to which this socket is connected. Returns null
if the socket is not connected.
If the socket was connected prior to being closed
, then this method will continue to return the connected address after the socket is closed.
public int getPort()
Returns the port number to which this socket is connected. Returns -1
if the socket is not connected.
If the socket was connected prior to being closed
, then this method will continue to return the connected port number after the socket is closed.
public SocketAddress getRemoteSocketAddress()
Returns the address of the endpoint this socket is connected to, or null
if it is unconnected.
If the socket was connected prior to being closed
, then this method will continue to return the connected address after the socket is closed.
SocketAddress
representing the remote endpoint of this socket, or null
if it is not connected yet.getInetAddress()
, getPort()
, connect(SocketAddress)
public SocketAddress getLocalSocketAddress()
Returns the address of the endpoint this socket is bound to.
SocketAddress
representing the local endpoint of this socket, or null
if it is closed or not bound yet.getLocalAddress()
, getLocalPort()
, bind(SocketAddress)
public void send(DatagramPacket p) throws IOException
Sends a datagram packet from this socket. The DatagramPacket
includes information indicating the data to be sent, its length, the IP address of the remote host, and the port number on the remote host.
If there is a security manager, and the socket is not currently connected to a remote address, this method first performs some security checks. First, if p.getAddress().isMulticastAddress()
is true, this method calls the security manager's checkMulticast
method with p.getAddress()
as its argument. If the evaluation of that expression is false, this method instead calls the security manager's checkConnect
method with arguments p.getAddress().getHostAddress()
and p.getPort()
. Each call to a security manager method could result in a SecurityException if the operation is not allowed.
p
- the DatagramPacket
to be sent.IOException
- if an I/O error occurs.SecurityException
- if a security manager exists and its checkMulticast
or checkConnect
method doesn't allow the send.PortUnreachableException
- may be thrown if the socket is connected to a currently unreachable destination. Note, there is no guarantee that the exception will be thrown.IllegalBlockingModeException
- if this socket has an associated channel, and the channel is in non-blocking mode.IllegalArgumentException
- if the socket is connected, and connected address and packet address differ.DatagramPacket
, SecurityManager.checkMulticast(InetAddress)
, SecurityManager.checkConnect(java.lang.String, int)
public void receive(DatagramPacket p) throws IOException
Receives a datagram packet from this socket. When this method returns, the DatagramPacket
's buffer is filled with the data received. The datagram packet also contains the sender's IP address, and the port number on the sender's machine.
This method blocks until a datagram is received. The length
field of the datagram packet object contains the length of the received message. If the message is longer than the packet's length, the message is truncated.
If there is a security manager, a packet cannot be received if the security manager's checkAccept
method does not allow it.
p
- the DatagramPacket
into which to place the incoming data.IOException
- if an I/O error occurs.SocketTimeoutException
- if setSoTimeout was previously called and the timeout has expired.PortUnreachableException
- may be thrown if the socket is connected to a currently unreachable destination. Note, there is no guarantee that the exception will be thrown.IllegalBlockingModeException
- if this socket has an associated channel, and the channel is in non-blocking mode.DatagramPacket
, DatagramSocket
public InetAddress getLocalAddress()
Gets the local address to which the socket is bound.
If there is a security manager, its checkConnect
method is first called with the host address and -1
as its arguments to see if the operation is allowed.
null
if the socket is closed, or an InetAddress
representing wildcard
address if either the socket is not bound, or the security manager checkConnect
method does not allow the operationSecurityManager.checkConnect(java.lang.String, int)
public int getLocalPort()
Returns the port number on the local host to which this socket is bound.
-1
if the socket is closed, or 0
if it is not bound yet.public void setSoTimeout(int timeout) throws SocketException
Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a call to receive() for this DatagramSocket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the DatagramSocket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0
. A timeout of zero is interpreted as an infinite timeout.
timeout
- the specified timeout in milliseconds.SocketException
- if there is an error in the underlying protocol, such as an UDP error.getSoTimeout()
public int getSoTimeout() throws SocketException
Retrieve setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).
SocketException
- if there is an error in the underlying protocol, such as an UDP error.setSoTimeout(int)
public void setSendBufferSize(int size) throws SocketException
Sets the SO_SNDBUF option to the specified value for this DatagramSocket
. The SO_SNDBUF option is used by the network implementation as a hint to size the underlying network I/O buffers. The SO_SNDBUF setting may also be used by the network implementation to determine the maximum size of the packet that can be sent on this socket.
As SO_SNDBUF is a hint, applications that want to verify what size the buffer is should call getSendBufferSize()
.
Increasing the buffer size may allow multiple outgoing packets to be queued by the network implementation when the send rate is high.
Note: If send(DatagramPacket)
is used to send a DatagramPacket
that is larger than the setting of SO_SNDBUF then it is implementation specific if the packet is sent or discarded.
size
- the size to which to set the send buffer size. This value must be greater than 0.SocketException
- if there is an error in the underlying protocol, such as an UDP error.IllegalArgumentException
- if the value is 0 or is negative.getSendBufferSize()
public int getSendBufferSize() throws SocketException
Get value of the SO_SNDBUF option for this DatagramSocket
, that is the buffer size used by the platform for output on this DatagramSocket
.
DatagramSocket
SocketException
- if there is an error in the underlying protocol, such as an UDP error.setSendBufferSize(int)
public void setReceiveBufferSize(int size) throws SocketException
Sets the SO_RCVBUF option to the specified value for this DatagramSocket
. The SO_RCVBUF option is used by the the network implementation as a hint to size the underlying network I/O buffers. The SO_RCVBUF setting may also be used by the network implementation to determine the maximum size of the packet that can be received on this socket.
Because SO_RCVBUF is a hint, applications that want to verify what size the buffers were set to should call getReceiveBufferSize()
.
Increasing SO_RCVBUF may allow the network implementation to buffer multiple packets when packets arrive faster than are being received using receive(DatagramPacket)
.
Note: It is implementation specific if a packet larger than SO_RCVBUF can be received.
size
- the size to which to set the receive buffer size. This value must be greater than 0.SocketException
- if there is an error in the underlying protocol, such as an UDP error.IllegalArgumentException
- if the value is 0 or is negative.getReceiveBufferSize()
public int getReceiveBufferSize() throws SocketException
Get value of the SO_RCVBUF option for this DatagramSocket
, that is the buffer size used by the platform for input on this DatagramSocket
.
DatagramSocket
SocketException
- if there is an error in the underlying protocol, such as an UDP error.setReceiveBufferSize(int)
public void setReuseAddress(boolean on) throws SocketException
Enable/disable the SO_REUSEADDR socket option.
For UDP sockets it may be necessary to bind more than one socket to the same socket address. This is typically for the purpose of receiving multicast packets (See MulticastSocket
). The SO_REUSEADDR
socket option allows multiple sockets to be bound to the same socket address if the SO_REUSEADDR
socket option is enabled prior to binding the socket using bind(SocketAddress)
.
Note: This functionality is not supported by all existing platforms, so it is implementation specific whether this option will be ignored or not. However, if it is not supported then getReuseAddress()
will always return false
.
When a DatagramSocket
is created the initial setting of SO_REUSEADDR
is disabled.
The behaviour when SO_REUSEADDR
is enabled or disabled after a socket is bound (See isBound()
) is not defined.
on
- whether to enable or disable theSocketException
- if an error occurs enabling or disabling the SO_RESUEADDR
socket option, or the socket is closed.getReuseAddress()
, bind(SocketAddress)
, isBound()
, isClosed()
public boolean getReuseAddress() throws SocketException
Tests if SO_REUSEADDR is enabled.
boolean
indicating whether or not SO_REUSEADDR is enabled.SocketException
- if there is an error in the underlying protocol, such as an UDP error.setReuseAddress(boolean)
public void setBroadcast(boolean on) throws SocketException
Enable/disable SO_BROADCAST.
Some operating systems may require that the Java virtual machine be started with implementation specific privileges to enable this option or send broadcast datagrams.
on
- whether or not to have broadcast turned on.SocketException
- if there is an error in the underlying protocol, such as an UDP error.getBroadcast()
public boolean getBroadcast() throws SocketException
Tests if SO_BROADCAST is enabled.
boolean
indicating whether or not SO_BROADCAST is enabled.SocketException
- if there is an error in the underlying protocol, such as an UDP error.setBroadcast(boolean)
public void setTrafficClass(int tc) throws SocketException
Sets traffic class or type-of-service octet in the IP datagram header for datagrams sent from this DatagramSocket. As the underlying network implementation may ignore this value applications should consider it a hint.
The tc must be in the range 0 <= tc <=
255
or an IllegalArgumentException will be thrown.
Notes:
For Internet Protocol v4 the value consists of an integer
, the least significant 8 bits of which represent the value of the TOS octet in IP packets sent by the socket. RFC 1349 defines the TOS values as follows:
IPTOS_LOWCOST (0x02)
IPTOS_RELIABILITY (0x04)
IPTOS_THROUGHPUT (0x08)
IPTOS_LOWDELAY (0x10)
Setting bits in the precedence field may result in a SocketException indicating that the operation is not permitted.
for Internet Protocol v6 tc
is the value that would be placed into the sin6_flowinfo field of the IP header.
tc
- an int
value for the bitset.SocketException
- if there is an error setting the traffic class or type-of-servicegetTrafficClass()
public int getTrafficClass() throws SocketException
Gets traffic class or type-of-service in the IP datagram header for packets sent from this DatagramSocket.
As the underlying network implementation may ignore the traffic class or type-of-service set using setTrafficClass(int)
this method may return a different value than was previously set using the setTrafficClass(int)
method on this DatagramSocket.
SocketException
- if there is an error obtaining the traffic class or type-of-service value.setTrafficClass(int)
public void close()
Closes this datagram socket.
Any thread currently blocked in receive(java.net.DatagramPacket)
upon this socket will throw a SocketException
.
If this socket has an associated channel then the channel is closed as well.
close
in interface Closeable
close
in interface AutoCloseable
public boolean isClosed()
Returns whether the socket is closed or not.
public DatagramChannel getChannel()
Returns the unique DatagramChannel
object associated with this datagram socket, if any.
A datagram socket will have a channel if, and only if, the channel itself was created via the DatagramChannel.open
method.
null
if this socket was not created for a channelpublic static void setDatagramSocketImplFactory(DatagramSocketImplFactory fac) throws IOException
Sets the datagram socket implementation factory for the application. The factory can be specified only once.
When an application creates a new datagram socket, the socket implementation factory's createDatagramSocketImpl
method is called to create the actual datagram socket implementation.
Passing null
to the method is a no-op unless the factory was already set.
If there is a security manager, this method first calls the security manager's checkSetFactory
method to ensure the operation is allowed. This could result in a SecurityException.
fac
- the desired factory.IOException
- if an I/O error occurs when setting the datagram socket factory.SocketException
- if the factory is already defined.SecurityException
- if a security manager exists and its checkSetFactory
method doesn't allow the operation.DatagramSocketImplFactory.createDatagramSocketImpl()
, SecurityManager.checkSetFactory()
© 1993–2017, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.