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

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2 thoughts on “Create random files with random content with Java”

  1. It looks good. The only thing I’d consider, and entirely depending on what you are testing for, is changing the file names to be different sizes and contain more international characters. I feel like I test and test with standardized names, and always run into more interesting issues when I have very long file names or ones in Arabic or Cyrillic. It may not matter, but if it does, you’d rather figure it out early.

  2. As you said, there are a lot of possibilities. A one-liner in Linux to create 1000 files of 1 GB random data:
    for((i=1000; i<2000; i++)); do echo "${i:1}"; dd if=/dev/urandom of=${i:1}.bin bs=1024M count=1; done

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