executing a .class from a java file with java commands in it

Question

import java.io.*;

public class chk 
{
String command;
public String  getMsg(String fileName,File Path1) 
{
    String dir,name=" ";
    int x;
    x=fileName.indexOf(".class");name=fileName.substring(0, x);
    command ="java " + name +" < C:\\iptest\\input.txt > C:\\outtest\\"+name+".txt";
    String output = executeCommand(command,Path1);
    if(output.compareTo("")==0)             
        output = "Compilation Successfull!!";
    return output;
}
private String executeCommand(String command,File Path1) 
{
    StringBuffer output = new StringBuffer();
    Process p;
    try 
    {
        p = Runtime.getRuntime().exec(command,null,Path1);
        //p.waitFor();
        BufferedReader reader1 = new BufferedReader(new InputStreamReader(p.getErrorStream()));
        BufferedReader reader2 = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line = "";           
        while ((line = reader1.readLine())!= null) 
        {
            output.append(line + "\n");
        }
        while ((line = reader2.readLine())!= null) 
        {
            output.append(line + "\n");
        }
    } catch (Exception e) 
    {
        e.printStackTrace();
    }
    return output.toString();
}
public static void main(String args[])throws IOException
{
    String x;
    File dir=new File("C:\\Users\\RONEET\\Desktop");
    chk ob=new chk();
    x=ob.getMsg("hello.class",dir);
    System.out.println("OUtput : "+x);
}
 }

What I am doing in this file is i am executing a hello.class file from a java file and storing its output as a txt file at the following location C:\outtest\ with a proper file name. But when i compile the above file my program goes into some kind of infinite loop and never terminates .

window stays like this enter image description here

EDITED : hello.java

import java.io.*;
class hello
{
public static void main(String agrs[])throws IOException
{
    BufferedReader s=new BufferedReader(new InputStreamReader(System.in));
    String str;
    str=s.readLine();
    System.out.print(str+"\n");
}
}

Why is one Java program invoking another? Would it not make more sense to use the `Hello` class directly? — , Feb 14 '14 at 17:24
@JohnGaughan different application have different requirements mine needs this that is why i am working on it — rick, Feb 14 '14 at 17:28
@rick that is the reason for the first word in my comment: "why." I was curious about the requirement. Maybe there is a better way? — , Feb 14 '14 at 17:31
@JohnGaughan I am building an application that can compile programs written on different languages . — rick, Feb 14 '14 at 17:34
p.waitFor(); after the whiles? And the whiles should't be threads? — Leo, Feb 14 '14 at 17:36

score 1 · Accepted Answer · edited May 23 '17 at 11:57

disclaimer - I've figured out that my solution could work except if I used STDIN and STDOUT redirection with < and >. So I am using the same solution presented here Running external program with redirected stdin and stdout from Java

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class Runner {

    public static void pipeStream(InputStream input, OutputStream output) throws IOException {
        byte buffer[] = new byte[1024];
        int numRead = 0;

        do {
            numRead = input.read(buffer);
            output.write(buffer, 0, numRead);
        } while (input.available() > 0);

        output.flush();
    }

    public static void main(String[] argv) {
        File dir = new File("C:\\Users\\Leo\\workspace\\STackOverflow\\src\\");
        FileInputStream fileIn = null;
        FileOutputStream fileOut = null;

        OutputStream procIn = null;
        InputStream procOut = null;

        try {
            fileIn = new FileInputStream(new File(dir, "input.txt"));
            fileOut = new FileOutputStream(new File(dir, "output.txt"));

            Process process = Runtime.getRuntime().exec("C:\\jdk1.7.0_51\\bin\\java Hello", null, dir);
            procIn = process.getOutputStream();
            procOut = process.getInputStream();

            pipeStream(fileIn, procIn);
            pipeStream(procOut, fileOut);
        } catch (IOException ioe) {
            System.out.println(ioe);
        }
    }
}

given

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


public class Hello {

    /**
     * @param args
     */
    public static void main(String[] args) {
        try{
            BufferedReader br = 
                          new BufferedReader(new InputStreamReader(System.in));

            String input;

            while((input=br.readLine())!=null){
                System.out.println("processed"+input);
            }

        }catch(IOException io){
            io.printStackTrace();
        }   

    }

}

this is pretty much the same as

"java Hello < input.txt > output.txt"

given input.txt like

it generates output.txt like

processed1
processed2
processed3
processed4

I know, the two loggers are strange. You don't need them. But all the rest can help I think ;-) — Leo, Feb 14 '14 at 17:40
how to execute "java hello < C:\iptest\input.txt > C:\outtest\hello.txt" command with this code of yours ? — rick, Feb 14 '14 at 17:41
It will be very helpful if you can edit your code with this command of mine — rick, Feb 14 '14 at 17:42
my code sucks, I know :-) let me try to improve it. I always try to help poor people like me — Leo, Feb 14 '14 at 18:15

score 0 · Answer 2 · answered Feb 14 '14 at 17:34

0

The reading of the streams is probably blocking. You could try putting the stream reading into separate threads.

answered Feb 14 '14 at 17:34

Choker

875
6
9

executing a .class from a java file with java commands in it

2 Answers2

Linked