Java programming uses UDP to establish a code example of group chat system

Introduction to related Java classes

DatagramSocket

public class DatagramSocket extends Object

This class represents the socket used to send and receive datagram packets.

Datagram socket is the sending or receiving point of 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 choose different routes or arrive in different orders.

UDP broadcast sending is always enabled on datagram socket. In order to receive broadcast packets, datagram socket should be bound to a wildcard address. In some implementations, broadcast packets can also be received when datagram socket is bound to a more specific address

You can send and receive data through send and receive of datagram socket

public void receive(DatagramPacket p) throws IOException

Receive datagram packets from this socket. When this method returns, the buffer of datagram packet is filled with the received data. The datagram packet also contains the IP address of the sender and the port number on the sender's machine.

This method is blocked until the datagram is received. The length field of the datagram packet object contains the length of the received information. If the message is longer than the length of the packet, the message will be truncated

If there is a security manager and the checkaccept method of the security manager does not allow receiving operations, the package cannot be received.

Parameters:

P - datagram packet to place the incoming data.

Throw:

IOException - if an I / O error occurs.

SocketTimeoutException- if the setSoTimeout was previously called and the timeout value passed.

Portunreachableexception - may be thrown when a socket connects to a currently unreachable target. Note that there is no guarantee that this exception will be thrown.

Illegalblockingmodeexception - if this socket has an associated channel and the channel is in non blocking mode.

public void send(DatagramPacket p) throws IOException

Send datagram packets from this socket. The datagram packet contains information indicating the data to be sent, its length, the IP address of the remote host and the port number of the remote host

If a security manager exists and the socket is not currently connected to a remote address, this method first performs some security checks. First, if p.getaddress() If ismulticastaddress() is true, this method calls the checkmulticast method of the security manager with p.getaddress() as a parameter. If the value of the expression is false, this method calls the p.getaddress () of the security manager instead Checkconnect method with gethostaddress () and p.getport () as parameters. If this operation is not allowed, every call to the security manager method will result in SecurityException.

Parameters:

P - datagram packet to be sent.

Throw:

IOException - if an I / O error occurs.

SecurityException - if the security manager exists and its checkmulticast or checkconnect methods do not allow sending.

Portunreachableexception - may be thrown when a socket connects to a currently unreachable target. Note that there is no guarantee that this exception will be thrown.

Illegalblockingmodeexception - if this socket has an associated channel and the channel is in non blocking mode.

DatagramPacket

public final class DatagramPacket extends Object

This class represents UDP datagram packet, which is used to realize connectionless packet delivery service

Construction method:

DatagramPacket(byte[]buf,intlength)

Construct datagram packet to receive data packets with length

DatagramPacket(byte[]buf,intlength,InetAddressaddress,intport)

Construct datagram packet, which is used to send the packet with length to the specified port number on the specified host

Example of UDP group chat system

UDP is for connectionless. Group chat is to send data to broadcast address, so that everyone will receive messages; In the way of thread, start a sender thread and receiver thread. The sender reads the keyboard input as output, and the receiver reads the input information and displays it

Sender

UdpSender. java

Receiver

UdpReceiver. java

Main method

UdpMain. java

test result

The input side reads the keyboard input as output, and the receiver receives the message and displays the sender's IP and host name

summary

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