You can write  a batch (.bat on Windows OS) or shell script (.sh on Linux OS) file
which performs the exact copy.
for example in Windows you can have "copy.bat" with this contents:

copy "%1" "%2"

and then you can call  

exec("PATH_TO_COPY_BAT/copy.bat d:/music/someFile.txt d:/downloads");

Alternatively you can do it with java. Read the contents of the file  with BufferedReader and write it to a newly created file with BufferedWriter. Use buffer to improve the performance:

bytes buffer = new byte[BUFFER_SIZE];
...
while (reader.read(buffer) != -1)
writer.write(buffer);
...