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Thread: ProcessBuilder and I/O

  1. #1
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    Default ProcessBuilder and I/O

    I'm trying to get my head around the ProcessBuilder class, so I built this test class. Needless to say, it doesn't work, but I can't figure out why. Here's the code:

    import java.io.*;
     
     
    /*Test Class*/
    public class TestMe
    {
    	public static void main(String[] args)
    	{
    		ProcessBuilder pb = null;
    		Process shell = null;
    		BufferedReader fromProcess = null;
    		BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
    		PrintWriter toProcess = null;
    		String command = "";
    		String line = "";
     
    		try
    		{
    			System.out.printf("-------------\n");
    			System.out.printf("Testing Process Builder%n");
    			pb = new ProcessBuilder ("/bin/bash");
    			System.out.printf("Merge stdout with stderr? %b%n", pb.redirectErrorStream());
    			if (pb.redirectErrorStream() != true)
    			{
    				System.out.printf("\tMerging both streams%n");
    				pb.redirectErrorStream(true);
    				System.out.printf("\tIt is now %b%n", pb.redirectErrorStream());
    			}
     
    			System.out.printf("Creating Shell process\n");
    			shell = pb.start();
    			System.out.printf("Getting stdout\n");
    			fromProcess = new BufferedReader (new InputStreamReader (shell.getInputStream()));
    			System.out.printf("Getting stdin\n");
    			toProcess = new PrintWriter (shell.getOutputStream(), true);
     
    			System.out.printf("Time to pass a command!%n");
    			System.out.printf("\tstdin :- ");
    			command = input.readLine();
    			System.out.printf("\tCommand is: %s%n", command);
    			System.out.printf("Handing command over to process...%n");
    			toProcess.print(command);
     
    			System.out.printf("Getting output...%n");
    			do
    			{
    				line = fromProcess.readLine();
    				System.out.printf("\t%s%n",line);
    			} while (line != null);
     
    			//Close I/O
    			toProcess.close();
    			fromProcess.flush();
    			fromProcess.close();
     
    			System.printf("It Worked!%n");
     
    		}
    		catch (Exception e)
    		{
    			System.out.printf("%nError: %s%n", e.getMessage());
    			e.printStackTrace();
    		}
     
    	} //End main method
     
    } //End class TestMe




    In my head, I should be able to pass a command (say, "ls") and get the output of the command printed out to the screen. Where am I going wrong? Any help would be greatly appreciated.


    Zo...


  2. #2
    Administrator copeg's Avatar
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    Default Re: ProcessBuilder and I/O

    See this article: When Runtime.exec() won't - JavaWorld