p.waitfor() waits forever

Question

i am trying to run commands using java program,but p.waitfor() function waits forever.What is wrong with the code?

import java.io.*;

public class doscmd
{
  public static void main(String args[]) throws InterruptedException
  {
    try
    {
      Process p=Runtime.getRuntime().exec("cmd /c dir");
      p.waitFor();
      BufferedReader reader=new BufferedReader(new InputStreamReader(p.getInputStream()));
      String line=reader.readLine();
      while(line!=null)
      {
        System.out.println(line);
        line=reader.readLine();
      }
    } 
    catch(IOException e1) {}


    System.out.println("Done");
  }
}

The program seems to work fine without `waitFor()`. Why do you need it? — Paul Grime, Feb 01 '12 at 20:03

score 5 · Accepted Answer · answered Feb 01 '12 at 20:01

5

Is the directory large? Maybe p fills up its output buffer and stalls waiting for a reader to consume something so it can finish writing out the directory listing.

You should probably move

p.waitFor();

to the end of the method.

answered Feb 01 '12 at 20:01

Mike Samuel

118,113
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score 1 · Answer 2 · edited May 23 '17 at 12:32

1

You have to access your InputStream and ErrorStream before you're calling waitFor(). You should take a look at that question too for more details on how it works.

edited May 23 '17 at 12:32

Community

1
1

answered Feb 01 '12 at 20:03

talnicolas

13,885
7
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56

score 1 · Answer 3 · answered Feb 01 '12 at 20:08

Your directory structure is too large. Move your p.waitfor() to

Process p=Runtime.getRuntime().exec("cmd /c dir");
BufferedReader reader=new BufferedReader(new InputStreamReader(p.getInputStream()));
String line=reader.readLine();
while(line!=null)
{
System.out.println(line);
line=reader.readLine();
}
p.waitFor();

I tried running running this in C:\programfiles works fine.

p.waitfor() waits forever

3 Answers3