How to execute multiple windows commands using Runtime class in java

Question

I am trying to execute windows commands from Java using the following code,

Process p=Runtime.getRuntime().exec("wget www.anyurl.com/index.html);

and it works but when I try to execute another command which is as follows,

Process p1=Runtime.getRuntime().exec("pscp -pw sysadmin c:/mydirectory/mypage.html mahesh@vmstni01:/home/usr");

it does not seem to work. If I comment out the first process line (ie Process p) then the process p1 is working fine, it executes and shows that file has been copied successfully. Please can anyone tell me why this is happening?

does the first command have to be completed before the second one can be called successfully? — David Kroukamp
– David Kroukamp, Commented Jun 24, 2012 at 18:47
Hi JB Nizet, first command works fine (i e wget) but when I try to execute pscp it is not working and if I comment first line (ie Process p=Runtime.getRuntime().exec("wget www.anyurl.com/index.html); ) then pscp is working fine. — Mahesh
– Mahesh, Commented Jun 24, 2012 at 19:00
"It doesn't work" doesn't explain what happens. Does the program hang? Does it throw an exception? If so, what's the stack trace? Does it do something other than what you expect? If so what do you expect it to do and what does it do instead? When you go to a doctor, you don't just say: I'm sick. You tell all the symptoms, to help him identify what's wrong. Do the same here. — JB Nizet
– JB Nizet, Commented Jun 24, 2012 at 19:20

Community · Accepted Answer · 2017-05-23 10:09:18Z

4

You need to clean up the streams of the first process, otherwise the program will block because the "wget" process produces output that is never read in your current implementation. You need to sort out the output and error streams of the first process. Look at answers to e.g. another question about java-runtime-exec on SO.

The code below works for reference, but relies on the fact that wget generates output to stderr and pscp to stdout. If anything gets output to the other corresponding stream, the code works as long as the output fits into the buffer of the Java program (please note that these buffer sizes tend to be different from platform to platform) while it empties the first stream. If the buffer gets full, the execution of the command simply blocks. You should create a separate thread for both, stout and stderr that reads the appropriate stream of the process.

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

...

    Process p=Runtime.getRuntime().exec("wget http://www.duckduckgo.com/");

    BufferedReader perr=new BufferedReader(new InputStreamReader(p.getErrorStream()));
    BufferedReader pout=new BufferedReader(new InputStreamReader(p.getInputStream()));
    // We read stderror first from wget, because it spits the progress information into stderr
    for (String s=perr.readLine(); s!=null; s=perr.readLine())
    {
        System.out.println("Stderr from p: "+s);
    }
    for (String s=pout.readLine(); s!=null; s=pout.readLine())
    {
        System.out.println("Stdout from p: "+s);
    }
    // if you need to check whether the command actually returned normally
    int returnCode = p.waitFor();
    perr.close();
    pout.close();

    System.out.println("Returned from p with exit code "+returnCode);

    p=Runtime.getRuntime().exec("pscp -pw dontuseplainpwusesshkeys index.html [email protected]:");
    perr=new BufferedReader(new InputStreamReader(p.getErrorStream()));
    pout=new BufferedReader(new InputStreamReader(p.getInputStream()));
    // We read stdout of pscp first because pscp spits stuff into stdout.
    // The process will block if the buffer gets full and does not get emptied.
    for (String s=pout.readLine(); s!=null; s=pout.readLine())
    {
        System.out.println("Stdout from p: "+s);
    }
    for (String s=perr.readLine(); s!=null; s=perr.readLine())
    {
        System.out.println("Stderr from p: "+s);
    }

    int returnCode1 = p.waitFor();
    perr.close();
    pout.close();

    System.out.println("Process exited with return code "+returnCode1);

edited May 23, 2017 at 10:09

CommunityBot

11 silver badge

answered Jun 24, 2012 at 18:50

jpe

1,0517 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

Mahesh Over a year ago

Hi David, first command is working fine before second command executes

Mahesh Over a year ago

Hi jpe, I am trying with yours suggestion and get back to you.

Mahesh Over a year ago

Hi Guys, here I am providing my code please have look into it and tell me what wrong with this code, String input;BufferedReader br; br = new BufferedReader( new InputStreamReader( System.in ) ); input=br.readLine(); if(input.equals("download")) { Process p=Runtime.getRuntime().exec("wget www.anyurl.com/index.html); } else if(input.equals("upload")) { Process p1=Runtime.getRuntime().exec("pscp -pw sysadmin c:/mydirectory/mypage.html mahesh@vmstni01:/home/usr"); }

jpe Over a year ago

Look at the following post about p.getInputStream() and p.getErrorStream(): stackoverflow.com/a/8597030/1424507

Mahesh Over a year ago

Will you please modify my above code and tell me how it will look like. I tried with your suggestion but still not have success in my hands.

|

Collectives™ on Stack Overflow

How to execute multiple windows commands using Runtime class in java

1 Answer 1

9 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

9 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related