Excecuting dos (or unix) commands from Java.

[Azathoth]

I'm trying to excecute a command in dos from within my Java program, something like ("java " + commandline), but I can't get it to work.

This lcode is in Driver.java:

String commandline = "Cat file.txt";
Runtime rt1 = Runtime.getRuntime();
Process pr1 = rt1.exec("java " + commandline);

And this is my Cat.java, it prints the contents of the file(s) passed to it as arguments:

import java.io.*;

public class Cat {

   public static void main(String argv[]) {
      int counter = 0;
      while(counter < argv.length)
      {
         FileInputStream fin1;
         BufferedInputStream bin2;
  
         try {
            fin1 = new FileInputStream(argv[counter]);
         }
         catch (FileNotFoundException f) {
            throw new Error("The system cannot find the file " + argv[0]);
         }

         bin2 = new BufferedInputStream(fin1);
         byte[] bytes;
         boolean end;

         try {
            do {
               int avail = bin2.available();
               end = (avail == 0);
               bytes = new byte[avail];
               bin2.read(bytes);
               System.out.print(new String(bytes));
            } 
            while (!end);
            bin2.close();
            System.out.println("");
         }
         catch (IOException ex) {
            throw new Error("IO Error");
        }    
      counter++;
      }
   }
}

It looks like the command line is formatted correctly, but nothing happens upon execution...any help would be greatly appreciated.

 

[sedj]

You need to capture the IO streams from the Process object (see the documenation on Process to see how to get the streams).

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[Azathoth]

I've taken a look at the documenation on Process, but can't really make any sense of it. Any chance you could you provide a simple example?

 

[sedj]

InputStream is = process.getInputStream();
OutputStream os = process.getOutputStream();

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[stefanwagner]

If your program is a javaprogram, you don't need the Runtime-class.

Just call

Cat.main ("file.txt");

in Driver.java.

I guess the others have overseen that detail

Note: Either both classes have to share the same package-declaration, or 'Cat' has to be found in the classpath.

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