Class DatagramSocket

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.

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.

protected DatagramSocket(DatagramSocketImpl impl)

Creates an unbound datagram socket with the specified DatagramSocketImpl.

public DatagramSocket(SocketAddress bindaddr) throws SocketException

Creates a datagram socket, bound to the specified local socket address.

If the address is null an unbound socket will be created.

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.

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.

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.

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. A port number of zero will let the system pick up an ephemeral port in a bind operation.

If the IP address is a wildcard address, or is null, the socket will be bound to the wildcard address.

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.

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.

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 socket is already closed, then this method has no effect.

If this socket is not bound then this method will first cause the socket to be bound to an address that is assigned automatically, as if invoking the bind method with a parameter of null. 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.

Care should be taken to ensure that a connected datagram socket is not shared with untrusted code. 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. Datagrams in the socket's socket receive buffer, which have not been received before invoking this method, may be discarded.

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 given socket addresses IP address and port number, except that the SocketException that may be raised is not wrapped in an UncheckedIOException. Datagrams in the socket's socket receive buffer, which have not been received before invoking this method, may be discarded.

public void disconnect()

Disconnects the socket. If the socket is closed or not connected, then this method has no effect.

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.

public SocketAddress getLocalSocketAddress()

Returns the address of the endpoint this socket is bound to.

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.

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, and the socket is not currently connected to a remote address, a packet cannot be received if the security manager's checkAccept method does not allow it. Datagrams that are not permitted by the security manager are silently discarded.

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.

public int getLocalPort()

Returns the port number on the local host to which this socket is bound.

public void setSoTimeout(int timeout) throws SocketException

Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a positive timeout value, 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. A timeout of zero is interpreted as an infinite timeout. The option must be enabled prior to entering the blocking operation to have effect.

public int getSoTimeout() throws SocketException

Retrieve setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity).

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.

public int getSendBufferSize() throws SocketException

Get value of the SO_SNDBUF option for this DatagramSocket, that is the buffer size, in bytes, used by the platform for output on this DatagramSocket.

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 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.

public int getReceiveBufferSize() throws SocketException

Get value of the SO_RCVBUF option for this DatagramSocket, that is the buffer size, in bytes, used by the platform for input on this DatagramSocket.

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.

public boolean getReuseAddress() throws SocketException

Tests if SO_REUSEADDR is enabled.

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.

public boolean getBroadcast() throws SocketException

Tests if SO_BROADCAST is enabled.

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)

The last low order bit is always ignored as this corresponds to the MBZ (must be zero) bit.

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.

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.

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.

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.

@Deprecated(since="17") public 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.

public <T> DatagramSocket setOption(SocketOption<T> name, T value) throws IOException

Sets the value of a socket option.

public <T> T getOption(SocketOption<T> name) throws IOException

Returns the value of a socket option.

public Set<SocketOption<?>> supportedOptions()

Returns a set of the socket options supported by this socket. This method will continue to return the set of options even after the socket has been closed.

public void joinGroup(SocketAddress mcastaddr, NetworkInterface netIf) throws IOException

Joins a multicast group.

In order to join a multicast group, the caller should specify the IP address of the multicast group to join, and the local network interface to receive multicast packets from.

• The mcastaddr argument indicates the IP address of the multicast group to join. For historical reasons this is specified as a SocketAddress. The default implementation only supports InetSocketAddress and the port information is ignored.
• The netIf argument specifies the local interface to receive multicast datagram packets, or null to defer to the interface set for outgoing multicast datagrams. If null, and no interface has been set, the behaviour is unspecified: any interface may be selected or the operation may fail with a SocketException.

It is possible to call this method several times to join several different multicast groups, or join the same group in several different networks. However, if the socket is already a member of the group, an IOException will be thrown.

If there is a security manager, this method first calls its checkMulticast method with the mcastaddr argument as its argument.

public void leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf) throws IOException

Leave a multicast group on a specified local interface.

If there is a security manager, this method first calls its checkMulticast method with the mcastaddr argument as its argument.