Question

I am writing few programs to invoke cmd.exe with additional commands and collect the output generated from the same using java. Below is a sample program–

public class LoadShell {
    public static void main(String[] args) throws Exception {
    //Line1
        String [] command ={"cmd.exe","/c","dir"};      
    ProcessBuilder probuilder = new ProcessBuilder( command );             
        Process process = probuilder.start();       
        InputStream inputstream1 = process.getInputStream();        
        InputStreamReader inputstreamreader1 = new InputStreamReader(inputstream1);
        BufferedReader bufferedreader = new BufferedReader(inputstreamreader1);      
        String line="";
        while ((line = bufferedreader.readLine()) != null) {
            System.out.println(line);
        }

  }
}

These programs are working fine as expected. Now I have a simpler requirement. I want to invoke cmd.exe without any arguments and collect the output as String. This is because I want to send the process object reference and string to another method for some project specific purpose. So I have modified my code in Line1 as below–

public class LoadShell {
    public static void main(String[] args) throws Exception {
          //Line1
      String [] command ={"cmd.exe"};
      ProcessBuilder probuilder = new ProcessBuilder( command );             
          Process process = probuilder.start(); 
          InputStream inputstream1 = process.getInputStream();        
          InputStreamReader inputstreamreader1 = new InputStreamReader(inputstream1);
          BufferedReader bufferedreader = new BufferedReader(inputstreamreader1);
          int intch;     
        String line="";
        while ((line = bufferedreader.readLine()) != null) {
            System.out.println(line);
        }

       }
}

But in this case, the readLine method hangs indefinitely after printing–

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.

So I have also tried using read of BufferedReader instead of readline as follows —

while ((intch = bufferedreader.read()) != -1) {
            int ch = (char) intch;
            System.out.println(ch);
          }

But even read is hanging after reading the bytes corresponding to —

 Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

Is there any way I can get the complete output that is below without causing my program to hang —

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\devshankhasharm>

Any ideas would be appreciated.

Answer 1

Probably because without the /c flag you’re simply opening a shell window, and that external process is now sitting at the C:\> prompt waiting for a command to be issued. Since you never send anything, it’ll sit there until you kill it.