Running perl programs through java.

Question

How do i run a perl program through java?
arg.pl :
while(<STDIN>)
print;
java program that I tried:
import java.io.*;
class runtime
    static Process p;
    static BufferedReader stdOutput;
    static BufferedWriter stdInput;
    public static void main(String args[]) throws IOException
        int i = 0;
        try{
            String cmd[] = new String[] {"perl","arg.pl"};
            p = Runtime.getRuntime().exec(cmd,null,new File("./"));
            stdOutput = new BufferedReader(new InputStreamReader(p.getInputStream()));
            stdInput = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
        catch(Exception ex){
            System.out.println("Unable to initiate Process : " + ex);
        stdInput.write("abcd\n");
        stdInput.write("1234\n");
        stdInput.write("efgh\n");
        stdInput.write("5678\n");
        stdInput.close();
        System.out.println(stdOutput.readLine());
        System.out.println(stdOutput.readLine());
        System.out.println(stdOutput.readLine());
        System.out.println(stdOutput.readLine());
}This works well. But I need to read the output line by line as and when i give the standard input line by line to it.
I tried the following :
import java.io.*;
class runtime
    static Process p;
    static BufferedReader stdOutput;
    static BufferedWriter stdInput;
    public static void main(String args[]) throws IOException
        int i = 0;
        try{
            String cmd[] = new String[] {"perl","arg.pl"};
            p = Runtime.getRuntime().exec(cmd,null,new File("./"));
            stdOutput = new BufferedReader(new InputStreamReader(p.getInputStream()));
            stdInput = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
        catch(Exception ex){
            System.out.println("Unable to initiate Process : " + ex);
        stdInput.write("abcd\n");
        stdInput.flush();
        System.out.println(stdOutput.readLine());
        stdInput.write("1234\n");
        stdInput.flush();
        System.out.println(stdOutput.readLine());
        stdInput.write("efgh\n");
        stdInput.flush();
        System.out.println(stdOutput.readLine());
        stdInput.write("5678\n");
        stdInput.flush();
        System.out.println(stdOutput.readLine());
        stdInput.close();
}This doesn't work well. It just halts without any output.
Can anyone help me?
Edited by: Vijayakrishna on Dec 5, 2007 8:30 AM

Answer 1

Let me be more specific.
I want to use a class which will look something like this.
import java.io.*;
public class FindAnswer{
    Process p;
    BufferedReader stdOutput;
    BufferedWriter stdInput;
    public FindAnswer()
        try{
            String cmd[] = new String[] {"perl","arg.pl"};
            p = Runtime.getRuntime().exec(cmd,null,new File("./"));
            stdOutput = new BufferedReader(new InputStreamReader(p.getInputStream()));
            stdInput = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
        catch(Exception ex){
            System.out.println("Unable to initiate Process. Error: " + ex);
    public String getAnswer(String question)
        String answer = question;
        try{
            stdInput.write(question + System.getProperty("line.separator"));
            stdInput.flush();
            answer = stdOutput.readLine();
        catch(Exception ex){
            System.out.println("Exception. Error: " + ex);
        return answer;
    public void close()
        if (p != null) {
            try {
                if (p.getInputStream() != null)
                    p.getInputStream().close();
                if (p.getOutputStream() != null)
                    p.getOutputStream().close();
                if (p.getErrorStream() != null)
                    p.getErrorStream().close();
            catch (Exception e) {
                System.out.println("Exception in Closing Streams - " + e);
}The perl program takes lot of initialization time. I dont want to run the program foreach question i have. I'll just create an object to this class and find and answer by passing question to the object's getAnswer method. Here, I dont know all the questions in the beginning itself. I'll know one by one only and I should find answer without terminating the process.
Kindly help me in this.