Java stuck in infinite loop executing a wmic command on Windows Server 2003

Question

I'm trying to get a list of running processes and their file paths on a Windows Server 2003 machine. I'm using the following code to try and do that:

protected Map<String,String> getProcesses() {
    Map<String,String> processes = new HashMap<String,String>();
    try {
        String line;
        Process p = null;

        // Windows
        if (OS.indexOf("win") >= 0) {
            p = Runtime.getRuntime().exec("wmic process get description,executablepath");
            BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
            LOG.info("Entering while loop");
            while ((line = input.readLine()) != null) {
                LOG.info("blah");
                String[] array = line.split("\\s+");
                if (array.length > 1) {
                    processes.put(array[0], array[1]);
                }
            }
            LOG.info("Exited while loop");
            input.close();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return processes;
}

The program gets stuck in an infinite loop at the while condition. "blah" and "Exited while loop" never output to the log. I've ran the command in command prompt on both my win7 local machine and the server which outputs the information just fine. I've also ran the above code on my local machine which also works fine. It looks like it's some issue between Java and Windows Server 2003 that I haven't been able to find in the past 3 hours of googling. Any help would be much appreciated.

Answer 1

You will need to get and close your OutputStream before getting and using your InputStream . That will confirm to the process that you've started that you have finished sending input (in this case, no input) to the process.

p.getOutputStream().close();

Remember that on the Process object, getInputStream() input comes from the output stream of the process, and getOutputStream() output goes to the input stream of the process.

Answer 2

Remember the BufferedReader.readLine() operation will block if there the end of input has not been reached, see here .

I think what you are experiencing is explained in the API for Process :

The methods that create processes may not work well for special processes on certain native platforms, such as native windowing processes, daemon processes, Win16/DOS processes on Microsoft Windows, or shell scripts. The created subprocess does not have its own terminal or console. All its standard io (ie stdin, stdout, stderr) operations will be redirected to the parent process through three streams (getOutputStream(), getInputStream(), getErrorStream()). The parent process uses these streams to feed input to and get output from the subprocess. Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock.