A Java program which sends udp data.

sendUdpData.java

// A sample to send a udp data.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.io.File;

public class sendUdpData {

    static private int destPort;
    static private InetAddress destHost;
    static private String sendDataHexStr;
    static private final String USAGE = "Usage: java sendUdpData -host <target host> -port <target port> {-data <send data> | -file <file path>}";

    public static void main(String[] args) {
        try {
            // Set default values.
            destPort = 162;
            destHost = InetAddress.getByName("localhost");
            sendDataHexStr = "0102030405";

            setArgs(args);
            // Create packet data.
            byte sendData[] = hexStrToBin(sendDataHexStr);
            DatagramPacket dataPacket = new DatagramPacket(sendData, sendData.length, destHost, destPort);

            // Send trap.
            DatagramSocket dataSocket = new DatagramSocket();
            dataSocket.send(dataPacket);
            dataSocket.close();
        }
        catch (Exception e) {
            System.err.println("Error happened as follows.");
            System.err.println(e.getMessage());
            e.printStackTrace();
            System.err.println(USAGE);
        }
    }

    private static void setArgs(String[] args) {
        // Ex. -dest 127.0.0.1 -port 162 -data 0102030405
        for (int i=0; i< args.length; i++) {

            if ("-host".equals(args[i])) {
                try {
                    destHost = InetAddress.getByName(args[++i]);
                } catch (UnknownHostException e) {
                    System.err.println("The specified host is unknown. " +  USAGE);
                    System.exit(1);
                }
            }

            if ("-port".equals(args[i])) {
                try {
                    destPort = Integer.parseInt(args[++i]);
                } catch (Exception e) {
                    System.err.println("The specified port is invalid. " + USAGE);
                    System.exit(1);
                }
            }

            if ("-file".equals(args[i])) {
                File inputFile = new File(args[++i]);
                if (!inputFile.isFile()) {
                    System.err.println(args[i] + " is not a file.");
                    System.exit(1);
                }
                sendDataHexStr = removeSpaces(getFileContents(inputFile));
            }

            // If both "-file" and "-data" are specified, "-data" is used.
            if ("-data".equals(args[i])) {
                sendDataHexStr = args[++i];
            }
        }
    }

    private static String removeSpaces(String string) {
        StringBuilder stringWithoutSpace = new StringBuilder();
        for (int i=0; i<string.length(); i++) {
            if (string.charAt(i) == ' ') {
                continue;
            }
            stringWithoutSpace.append(string.charAt(i));
        }
        return stringWithoutSpace.toString();
    }

    private static String getFileContents(File file) {
        StringBuilder fileContents = new StringBuilder();
        try {
            BufferedReader br = new BufferedReader(new FileReader(file));
            String line;
            while ((line = br.readLine()) != null) {
                fileContents.append(line);
            }
        } catch (IOException e) {
            System.err.println("Can't read " + file.getAbsolutePath());
            System.exit(1);
        }
        return fileContents.toString();

    }

    private static byte[] hexStrToBin(String hexStr) {
        byte[] bin = new byte[hexStr.length() / 2];
        try {
            for (int i = 0; i < bin.length; i++) {
                // Change a hex string to a numeric value(binary value).
                // Ex. "3f" (‭0011 0011 ‭0110 0110‬‬)  ->  63 (0011 1111)
                bin[i] = (byte) Integer.parseInt(hexStr.substring(i * 2, i * 2 + 2), 16);
            }
        } catch (NumberFormatException e) {
            System.err.println("Send data is invalid. " + USAGE);
            System.exit(1);
        }
        return bin;
    }
}