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Java Net API

Posted by Kylin Soong on Aug 5, 2014 categorized as java

InetSocketAddress and InetAddress

InetAddress represents an Internet Protocol (IP) address. InetSocketAddress implements an IP Socket Address (IP address + port number) It can also be a pair (hostname + port number), in which case an attempt will be made to resolve the hostname.

The following private/public method used to get a InetAddress:

java.net.InetAddress#getByAddress(byte[])
java.net.InetAddress#getByAddress(java.lang.String, byte[])
java.net.InetAddress#getAllByName(java.lang.String)
java.net.InetAddress#getByName(java.lang.String)
java.net.InetAddress#getLocalHost()

The following constructor methods used to construct a InetSocketAddress:

public InetSocketAddress(int port)
public InetSocketAddress(InetAddress addr, int port)
public InetSocketAddress(String hostname, int port)

A Sample code snippets:

InetAddress inetAddress = InetAddress.getByName("localhost");
InetSocketAddress inetSocketAddress = new InetSocketAddress(inetAddress, 3100);

Socket socket = new Socket();
socket.setTcpNoDelay(true);//enable Nagle's algorithm to conserve bandwidth
socket.connect(inetSocketAddress);
socket.setSoTimeout(3000);

NetworkInterface

java.net.NetworkInterface represents a Network Interface made up of a name, and a list of IP addresses assigned to this interface. It is used to identify the local interface on which a multicast group is joined.

The bolow code snippets show how use NetworkInterface get all available addresses in a machine:

Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces();
while(en.hasMoreElements()){
    NetworkInterface intf = en.nextElement();
    System.out.println(intf.getName());
    Enumeration<InetAddress> addrs=intf.getInetAddresses();
    while(addrs.hasMoreElements())
        System.out.println("    " + addrs.nextElement());
}

A sample output as below:

tun0
    /10.72.7.161
docker0
    /172.17.42.1
vmnet8
    /fe80:0:0:0:250:56ff:fec0:8%vmnet8
    /172.16.209.1
vmnet1
    /fe80:0:0:0:250:56ff:fec0:1%vmnet1
    /192.168.173.1
em1
    /fe80:0:0:0:6af7:28ff:fe1b:3dc2%em1
    /192.168.1.105
lo
    /0:0:0:0:0:0:0:1%lo
    /127.0.0.1

DatagramSocket and MulticastSocket

java.net.DatagramSocket represents a socket for sending and receiving datagram packets.

A simple example of using DatagramSocket send and receive Message:

InetAddress receiverAddress = InetAddress.getLocalHost();
DatagramSocket socket = new DatagramSocket(new InetSocketAddress(InetAddress.getLocalHost(), 54321));
System.out.println("Maximum Send Buffer Size " + socket.getSendBufferSize() + ", Maximum Receive Buffer Size " + socket.getReceiveBufferSize());
		
byte[] senbuf = "0123456789".getBytes();
DatagramPacket packet = new DatagramPacket(senbuf, senbuf.length, receiverAddress, 54321);
socket.send(packet);
		
byte[] recbuf = new byte[10];
DatagramPacket recpacket = new DatagramPacket(recbuf, recbuf.length);
socket.receive(recpacket);
System.out.println(new String(recbuf));
		
socket.close();

java.net.MulticastSocket extends of java.net.DatagramSocket, with additional capabilities for joining “groups” of other multicast hosts on the internet.

A simple example of using MulticastSocket send and receive Message:

String msg = "Hello";
InetAddress group = InetAddress.getByName("228.5.6.7");
MulticastSocket s = new MulticastSocket(56789);
System.out.println("Maximum Send Buffer Size " + s.getSendBufferSize() + ", Maximum Receive Buffer Size " + s.getReceiveBufferSize());
s.joinGroup(group);
		
DatagramPacket hi = new DatagramPacket(msg.getBytes(), msg.length(), group, 56789);
s.send(hi);
		
byte[] buf = new byte[10];
DatagramPacket recv = new DatagramPacket(buf, buf.length);
s.receive(recv);
System.out.println(new String(buf));
		
s.leaveGroup(group);
s.close();