Java: Input a file to a process

Question

I am writing a simple Java project call Robot. The Robot can accept a config file from the command prompt (If there is not file, the robot will use the default config) by:

java Robot < config.txt

Does anyone know how I can read the redirect input from the command prompt in java?

Answer 1

You can access System.in as an input stream, that will contain all redirected input.

Specifically, reading from a redirected stdin is the same as reading from the regular stdin.

For example, let's say you want to read a list of integers from a redirected stream.

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class Foo {
    public static void main(String args[])
        throws IOException
    {
        BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
        int sum = 0;
        String line;
        while ((line = r.readLine()) != null) {
            sum += Integer.parseInt(line);
        }
        System.out.println(sum);
    }
}

Then when you run this, you'll get

$ (echo 1; echo 2; echo 65) > foo.txt
$ java Foo < foo.txt
68