Executing C++ programs in Java ?

[achana chan]

Why doesn't this C++ program execute in my code?
I've got an old C++ program (not from me) which takes 2 parameters: an ascii rawInputFile.in input file and parsedOutputFile.out which contains the cleansed data from the raw inputfile.
If I run the Solaris C++ program like this, it works:
Solaris#> $myCPlusProg rawInputFile.in parsedOutputFile.out > aLogFile.log
But if I embed it in Java as follows, throws following exception:
java.lang.NullPointerException at testdeltrdlck.main(Compiled code)

import java.io.*;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.*;
public class testdeltrdlck {  
    static PrintWriter out = new PrintWriter(System.out, true);  
    public static void main(String args[])  {      
        String command = null;      
        command ="$myCPlusProg rawInputFile.in parsedOutputFile.out > aLogFile.log";
        // command = "pwd";    //this one works
        out.println(command + "/n");      
        try      {        
             Runtime rt = Runtime.getRuntime();        
             Process prc = rt.exec(command);
             BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(prc.getInputStream()));
             String lineBuffer= null;
             while ((lineBuffer = bufferedReader.readLine()) != null)        {
                 out.println(lineBuffer);  }
        }//end try
        catch(IOException ioe)      {
            out.println("IO exception in command: " + command);}
        catch(Exception e)      {
              out.println("General Error"); }
    }// end main()
}//end deltrdlck class

[srinivasa varadhan]

hi,

can you tell me exactly in which line it throws NullPointerException, in your code..

Regards
Srinivas

[achana chan]

Error in command $myCPlusProg rawInputFile.in parsedOutputFile.out > aLogFile.log

java.lang.NullPointerException at deltrdlck.main(Compiled Code)

I was researching this and it seems that Runtime.exec() is rather limited and cannot do a unix redirect.

[Ernest Friedman-Hill]

Well, I don't see a class named deltrdlck here, and I also don't see how this program could throw a NullPointerException, and nothing prints "Error in command", so I suspect you're not showing us the actual code. Second, note that the "$" character demarcates shell variables, and it's exceedingly unlikely that you've got an actual binary whose name starts with a "$" -- Java isn't going to expand your shell variables for you, you'll need to use the actual name of the program!

Finally, as far as redirects go: Java is a cross-platform language, so you can't expect Runtime.exec() to understand the UNIX-specific concepts of output redirection. If you need to do this, then you can execute an instance of the shell, and tell the shell to do it -- i.e.,

String[] args = {
  "/bin/sh",
  "-c",
  "$myCPlusProg rawInputFile.in parsedOutputFile.out > aLogFile.log"
};
Runtime.getRuntime().exec(args);

Finally, note that in the command you're running, you're trying to redirect the output to a file. But then in your Java code, you're trying to read the output from the program. If the redirection succeeds, then there will be no output, right? You may need to sit and think a moment about what you actually want to do here.

[achana chan]

Thanks, that works.
Also thanks for explaining the significnance of "$".
Whatdoes the "-c" do?

[Ernest Friedman-Hill]

It's a switch to /bin/sh which tells it to execute the next argument as a command line. Windows CMD.EXE has a /C switch which does essentially the same thing.