Updated answer after learning that OP wants to duplicate streams
Since you want to write data in both streams try using TeeOutputStream
from Apache Commons. Change your code in second try to
try {
FileOutputStream fos = new FileOutputStream(f);
Runtime.getRuntime().addShutdownHook(new Thread(() -> {
try {
fos.flush();
}
catch (Throwable t) {
// Ignore
}
}, "Shutdown hook Thread flushing " + f));
//we will want to print in standard "System.out" and in "file"
TeeOutputStream myOut=new TeeOutputStream(System.out, fos);
PrintStream ps = new PrintStream(myOut, true); //true - auto-flush after println
System.setOut(ps);
} catch (Exception e) {
e.printStackTrace();
}
Now results from System.out
will also be placed in your file.