package com.example.tests;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class GroupDataGenerator {

	public static void main(String[] args) throws IOException {
		if (args.length < 3) {
			System.out.println("Please specify parameters: <amount of test data> <file> <format>");
			return;
		}
		
		int amount = Integer.parseInt(args[0]);
		File file = new File(args[1]);
		String format = args[2];
		
		List<GroupData> groups = generateRandomGroups(amount);
		if ("csv".equals(format)) {
			saveGroupsToCsvFile(groups, file);
		} else if ("xml".equals(format)) {
			saveGroupsToXmlFile(groups, file);
		} else {
			System.out.println("Unknown format <" + format + ">");
		}
	}

	private static void saveGroupsToXmlFile(List<GroupData> groups, File file) {
		// TODO Auto-generated method stub
		
	}

	private static void saveGroupsToCsvFile(List<GroupData> groups, File file) throws IOException {
		FileWriter writer = new FileWriter(file);	
		for (GroupData group : groups) {
			writer.write(group.getName() + "," + group.getHeader() + "," + group.getFooter() + "\n");
		}
		writer.close();
	}

	public static List<GroupData> generateRandomGroups(int amount) {
		List<GroupData> list = new ArrayList<GroupData>();
		for (int i = 0; i < amount; i++) {
			GroupData group = new GroupData()
					.withName(generateRandomString())
					.withHeader(generateRandomString())
					.withFooter(generateRandomString());
			list.add(group);
		}
		return list;
	}

	public static String generateRandomString() {
		Random rnd = new Random();
		if (rnd.nextInt(3) == 0) {
			return "";
		} else {
			return "test " + rnd.nextInt();
		}
	}
	
}

package com.example.tests;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class GroupDataGenerator {

	public static void main(String[] args) throws IOException {
		if (args.length < 3) {
			System.out.println("Please specify parameters: <amount of test data> <file> <format>");
			return;
		}
		
		int amount = Integer.parseInt(args[0]);
		File file = new File(args[1]);
		String format = args[2];
		
		if (file.exists()) {
			System.out.println("File exists, please remove it manually: \"" + file + "\"");
		}
		
		List<GroupData> groups = generateRandomGroups(amount);
		if ("csv".equals(format)) {
			saveGroupsToCsvFile(groups, file);
		} else if ("xml".equals(format)) {
			saveGroupsToXmlFile(groups, file);
		} else {
			System.out.println("Unknown format <" + format + ">");
		}
	}

	private static void saveGroupsToXmlFile(List<GroupData> groups, File file) {
		// TODO Auto-generated method stub
		
	}

	private static void saveGroupsToCsvFile(List<GroupData> groups, File file) throws IOException {
		FileWriter writer = new FileWriter(file);	
		for (GroupData group : groups) {
			writer.write(group.getName() + "," + group.getHeader() + "," + group.getFooter() + "\n");
		}
		writer.close();
	}

	public static List<GroupData> generateRandomGroups(int amount) {
		List<GroupData> list = new ArrayList<GroupData>();
		for (int i = 0; i < amount; i++) {
			GroupData group = new GroupData()
					.withName(generateRandomString())
					.withHeader(generateRandomString())
					.withFooter(generateRandomString());
			list.add(group);
		}
		return list;
	}

	public static String generateRandomString() {
		Random rnd = new Random();
		if (rnd.nextInt(3) == 0) {
			return "";
		} else {
			return "test " + rnd.nextInt();
		}
	}
	
}

add File exists check