Show stdout in file and in console (with System.setOut(new PrintStream(new File("output-file.txt"))

You could create a PrintWriter with an OutputStream that does both writes.

final OutputStream stdOut = System.out;
try {
    System.setOut(new PrintStream(new OutputStream() {
        private PrintStream ps = new PrintStream(new File("output-file.txt"));

        @Override
        public void write(int b) throws IOException {
            ps.write(b);
            stdOut.write(b);
        }

        @Override
        public void flush() throws IOException {
            super.flush();
            ps.flush();
            stdOut.flush();
        }

        @Override
        public void close() throws IOException {
            super.close();
            ps.close();
            // stdOut.close(); // Normally not done
        }
    }));
} catch (Exception e) {
    e.printStackTrace();
}

System.out.println("Hello, world!");

I never tried it, but i guess if you subclass the default Printstream you are able to print to console and file by yourself.

Something like:

class MyPrintStream extends printStream {

    private PrintStream secondPrinter;

    .....

    @Override 
    public void println(Object content) {
       super.println(content);
       secondPrinter.println(content);
    }
}

and maybe call it like this:

System.out = new MyPrintStream(myFile, System.out);

You can not use the systems OutputStream to write to 2 sources. It is a static variable and it can only have 1 value at a time.

You can try however, saving a reference to the consoles default OutputStream, and then changing the Systems OutputStream to your custom output stream, and write to both of them with a custom method.

You can make a new subclass of the PrintStream class and then override it's methods to write to a second Stream and then pass that to System.out as you've already one. Further reading & example implementation: https://books.google.ch/books?id=lbnjAwAAQBAJ&lpg=PA326&ots=j7OUeuXzIa&dq=java%20duplicate%20printstream&pg=PA326#v=onepage&q=java%20duplicate%20printstream&f=false