Create a file with a specific size in Java

Overview #

The java.io package offers classes that help us create and manage files. In this article, I’ll demonstrate how to create an empty file based on a filename and how to create a file with a certain size.

Code Examples #

Create an empty file #

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private File createFile(final String filename) throws IOException {
  File file = new File(filename);
  file.createNewFile();
  return file;
}

Note that this does not create missing parent folders. If you need to do this, call file.getParentFile().mkdirs() on line 3.

Create a file with a specific size #

We can use the RandomAccessFile class to create a file with a specific size.

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private File createFile(final String filename, final long sizeInBytes) throws IOException {
 File file = new File(filename);
  file.createNewFile();
  
  try (RandomAccessFile raf = new RandomAccessFile(file, "rw")) {
    raf.setLength(sizeInBytes);
  }
  
  return file;
}

Note that files created this way are populated with random data and may be treated as “sparse files” by the JVM implementation and the underlying operating system.