jodd-core/src/main/java/jodd/io/FileUtil.java
public static File mkdir(final File dir) throws IOException {
		if (dir.exists()) {
			checkIsDirectory(dir);
			return dir;
		}
		return checkCreateDirectory(dir);
	}
public static File mkdir(final File dir) throws IOException {
		if (dir.exists()) {
			checkIsDirectory(dir);
			return dir;
		}
		return checkCreateDirectory(dir);
	}
Creates single directory.

@throws IOException if cannot create directory.