When writing a Java code to transfer files via SFTP and FTPS you may need to consider that you will be transferring files of small, medium and large sizes. The way to create files of a certain size in a Linux operating system is to use Shell and the dd command. You can use /dev/random or /dev/zero as a data source or null bytes. The terms used are block size, count - which is for number of blocks, input file and output file. The total size of the file created will be bs multiplied count bytes.
dd input file =/dev/misc output file=filename.dat block size=1024 count
The above command creates file of 1024kb, with random data allocation.
Using dd to create a file of a specific size
The dd command allows you to create an empty file of particular size. Creating these arbitrary heavy files, may be useful for testing purposes.