Java NiO Learning Note eight Datagramchannel

Java NIO Datagramchannel

Java NIO Datagramchannel is a channel that can send and receive UDP packets. Because UDP is a non-connected network protocol, you cannot read and write to DatagramChannel other channels by default. instead, it sends and receives packets.

Open Datagramchannel

Open a DatagramChannel代码 :

Datagramchannel channel = datagramchannel.open (); Channel.socket (). Bind (new Inetsocketaddress (9999));

This example opens the DatagramChannel ability to receive packets on UDP port 9999.

Receive data

You can DatagramChannel receive data by calling the receive() method, as follows:

Bytebuffer buf = Bytebuffer.allocate; buf.clear (); channel.receive (BUF) ;

　　receive()Method copies the contents of the received packet to the given Buffer中 . If the received packet contains more data than Buffer can fit, the remaining data is silently discarded.

Send data

You can DatagramChannel send data by calling the send() method, as follows:

String newdata ="new string to write to file ..."                    + system.currenttimemillis ();     = Bytebuffer.allocate (buf.clear);buf.put (Newdata.getbytes ()); Buf.flip () ; int bytessent = channel.send (buf,new inetsocketaddress ("at.com", 80));

This example sends a string to the "jenkov.com" Server on UDP port 80. However, nothing is being listened to on the port, so nothing happens. You do not receive a notification that a packet is sent, because UDP has no guarantees for data transfer.

Connect to a specific address

You can connect a DatagramChannel to a specific address on the network. Because UDP is not connected, the way you connect to an address does not create a true connection like a TCP channel. Instead, it locks you DatagramChannel , so you can only send and receive packets from a specific address.

For example:

Channel.connect (new inetsocketaddress ("at.com", 80));

When connecting, you can also use read() and write() methods, just as you would with traditional channels. You have no warranties regarding the delivery of the data sent. Here are a few examples:

int bytesread = channel.read (buf);     int byteswritten = channel.write (BUF);

Java NiO Learning Note eight Datagramchannel