Day: November 15, 2020

Create random files with random content with Java

I was playing with DAOS in Domino 12 recently and needed a way to create thousands of test files with a given file size and random content.

I did not want to use existing files with real data for my tests. There are several programs available for Linux and Windows. Google for it. But as a developer, I should be able to create my one tool.

Here is some sample Java code that uses java.util.Random to create filnames and content in an easy way.

package de.eknori;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Random;

public class DummyFileCreator {
	static int filesize = 129 * 1024;
	static int count = 9500;

	static File dir = new File("c:\\temp\\dummy\\");
	static String ext = ".txt";

	public static void main(String[] args) {
		byte[] bytes = new byte[filesize];
		BufferedOutputStream bos = null;
		FileOutputStream fos = null;

		try {
			for (int i = 0; i < count; i++) {
				Random rand = new Random();

				String name = String.format("%s%s", System.currentTimeMillis(), rand.nextInt(100000) + ext);
				File file = new File(dir, name);

				fos = new FileOutputStream(file);
				bos = new BufferedOutputStream(fos);

				rand.nextBytes(bytes);
				bos.write(bytes);

				bos.flush();
				bos.close();
				fos.flush();
				fos.close();
			}

		} catch (FileNotFoundException fnfe) {
			System.out.println("File not found" + fnfe);
		} catch (IOException ioe) {
			System.out.println("Error while writing to file" + ioe);
		} finally {
			try {
				if (bos != null) {
					bos.flush();
					bos.close();
				}
				if (fos != null) {
					fos.flush();
					fos.close();
				}
			} catch (Exception e) {
				System.out.println("Error while closing streams" + e);
			}
		}
	}

}

The code is self-explanatory. Adjust the variables to your own needs, and you are ready to go