Running a .bat/ .cmd file from Java

[Raghu Devatha]

Hello,

I wanted to run a .cmd file from Java. I have something which works for me. Can someone help me understand possible failures of my program.

import java.io.IOException;

/*
  How to run a batch .bat or .cmd file from Java?
  1. I don't want the command window to open up. It should be in background.
  2. Gracefully destroy any new process created.
  3. Need to confirm the quality of the program with experts.
 */
public class RunBat {
    public static void main(String args[]) {
        Runtime run = Runtime.getRuntime();
        //The best possible I found is to construct a command which you want to execute
        //as a string and use that in exec. If the batch file takes command line arguments
        //the command can be constructed a array of strings and pass the array as input to
        //the exec method. The command can also be passed externally as input to the method.

        Process p = null;
        String cmd = "D:\\Database\\TableToCSV.cmd";
        try {
            p = run.exec(cmd);
            p.getErrorStream();
            System.out.println("RUN.COMPLETED.SUCCESSFULLY");
        }
        catch (IOException e) {
            e.printStackTrace();
            System.out.println("ERROR.RUNNING.CMD");
            p.destroy();
        }
    }
}

Is my solution reliable? How can I make sure that once the .cmd is execute there is no processes hanging around.

Thanks.

[Rene Larsen]

You need to tell the process which application that your cmd-file should be executed with.

e.g.

p = run.exec("cmd.exe /k " + cmd);

[Campbell Ritchie]

Raghu Devatha wrote:Is my solution reliable?

No. You need to "empty" the two Streams. Google for the classic article by Michael Daconta: Michael Daconta When Runtime.exec() won't, and follow what it says there. You can simplify the exercise slightly with the ProcessBuilder class, but follow Daconta's examples otherwise.

Moving as too difficult for "beginning".

[Steve Luke]

A good article to read is this one from Daconta:
When Runtime.exec() won't

Read through it and understand both what the Runtime.exec() is and is not, but also make sure you understand (and implements) the parts about consuming the output and error streams - failing to consume both (at the same time) can lead to the command stalling as it waits for buffers to free up.

<dern. Too Slow>

[Raghu Devatha]

Thanks for your suggestions. I read the article by Michel Daconta and understood most of it. The problem I am facing now with the approach suggested in the article is getting the exit value of the .cmd file.

I should have mentioned what actually I was doing there. I wanted to export a database table as a csv file. This is what I have done.

@echo off
sqlplus -l raghu/raghu@mydb @D:\SELF\Database\spool.sql
exit

spool.sql

set heading off;
set feedback off;
set flush off;
set linesize 1000;
set pagesize 5000;
SET COLSEP ',' ;

spool D:\SELF\Database\xxx.csv
select * from user_profile;
spool off
exit;

When I call the .cmd from Java, I dont get any exit code: When I run the Java class it hangs after printing <ERROR>

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

/*
  How to run a batch .bat or .cmd file from Java?
  1. We don't want the command window to open up. It should be in background.
  2. Gracefully destroy any new process created.
  3. Need to confirm the quality of the program with experts.
 */
public class RunBat {
    public static void main(String args[]) {
        Runtime run = Runtime.getRuntime();
        //The best possible I found is to construct a command which you want to execute
        //as a string and use that in exec. If the batch file takes command line arguments
        //the command can be constructed a array of strings and pass the array as input to
        //the exec method. The command can also be passed externally as input the method.

        Process p = null;
        String cmd = "D:\\SELF\\Database\\TableToCSV.cmd";
        //String cmd = "D:\\SELF\\Database\\test.cmd";
        try {
            p = run.exec("cmd.exe /c "+ cmd);
           // p = run.exec(cmd);
            InputStream stderr = p.getErrorStream();
            InputStreamReader isr = new InputStreamReader(stderr);
            BufferedReader br = new BufferedReader(isr);
            String line = null;
            System.out.println("<ERROR>");
            while ( (line = br.readLine()) != null)
                System.out.println(line);
            System.out.println("</ERROR>");
            int exitVal = p.exitValue();
            System.out.println("Process exitValue: " + exitVal);
            //TODO ; have to incorporate waitFor() properly
            //p.waitFor();
            //System.out.println(p.exitValue());
            //System.out.println(p.waitFor());
            System.out.println("RUN.COMPLETED.SUCCESSFULLY");
        }
        catch (IOException e) {
            System.out.println("ERROR.RUNNING.CMD");
            e.printStackTrace();
            p.destroy();
            p.exitValue();

        }
        /*catch (InterruptedException e2) {
            System.out.println("ERROR.RUNNING.CMD");
            e2.printStackTrace();
        }*/

        finally {
            p.destroy();
        }
    }

}

[Rob Spoor]

That's because you're only reading from the error stream. The process' output buffer is probably full, so you'll need to start reading from the Process' input stream as well. That's what the article is all about. And because you can't read from two streams simultaneously in one thread you'll need to use a new thread for the input stream. That, or use ProcessBuilder and redirect the error stream so you can read everything from the input stream.