Intro

SDIS FEUP MIEEC programming test solutions. Necessary tools for developing a UDP multicast and TCP client-server in Java.

A huge thanks to ZeD4805. All the Java source code was (almost) a direct copy of his solutions.

Java

UDP

For UDP the local network ip should be 230.0.0.0 and ports over 5000.

Multicast join

InetAddress multiCast_address = InetAddress.getByName(String ip);
InetSocketAddress inetSocketAddress = new InetSocketAddress(InetAddress multiCast_address, int multicast_port);
MulticastSocket multicast_socket = new MulticastSocket(int multicast_port);
multicast_socket.joinGroup(multiCastAddress);

Receive

DatagramPacket datagramPacket = new DatagramPacket(new byte[1000], 1000, inetSocketAddress); //Create packet to store data
multicastSocket.receive(DatagramPacket datagramPacket); //Wait for packet
String data = new String(datagramPacket.getData()); //Create string from byte array packet

Send

To convert from string to bytes a charset needs to be chosen. Include import java.nio.charset.*; and use StandardCharsets.UTF_8 .

byte[] msgBytes = s.getBytes(StandardCharsets.UTF_8); //Create byte array from string
DatagramPacket datagramPacket = new DatagramPacket(byte[] msgBytes, int msgBytes.length,InetSocketAddress group); //Create packet
multicastSocket.send(DatagramPacket datagramPacket); //Send packet

TCP

For TCP the local ip should be 127.0.0.1 and ports over 5000.

Socket creation

Normal socket:

Socket socket = new Socket(String server_ip, int port);

Server socket:

ServerSocket server_socket = new ServerSocket(int port);

A server socket waits until a sockets tries to connect to it:

Socket socket = server_socket.accept();

Datastream

DataStream are the streams used for the read and write operations

DataInputStream in = new DataInputStream(socket.getInputStream());

DataOutputStream out = new DataOutputStream(socket.getOutputStream());

Read/Write

Read and write functions have several versions for different variable types.

Read:

int received = in.readInt();

Write:

float avg = 10.15;
out.writeFloat(avg);

Timeout

Throws an exception after timeout ms without response :

socket.setSoTimeout(int timeout);

try{
    ...
}
catch (SocketException eTimeout) {
    ...
}

Closing socket

socket.close();

Check socket status

Check if socket is already available:

while(socket.isClosed());

Work while the socket is connected:

while(socket.isConnected()){
    ...
}

Utilities

Create Thread

Thread t = new Thread() {
    public void run() {
        ...
    }
}
t.start();

Delay

Thread.sleep(int period);

Parse

Integer:

int number = Integer.parseInt(String str);

Float:

float number = Float.parseFloat(String str);

Print

System.out.println("Something: " + data);

Loop through array of args

for (String s : Arrays.copyOfRange(String[] args, int starting_element , int args.length)){
    ...
}

JoaoGarrido/SDIS_Programming_Test_Solution