Question

Can anyone give me an example of how to stream the output of an external program executed with DefaultExecutor? I m not finding any documentation describing how to do this.

My external process will run for several hours, so just grabbing all output data isn t feasible; it must be streamed.

Answer 1

Note: this solution is synchronous, so it won t stream. You ll need to read is in a separate thread, or use the asynchronous version of the execute command.

private InputStream getStream() {

 String dataParsingCommand = "java";

PipedOutputStream output = new PipedOutputStream();
PumpStreamHandler psh = new PumpStreamHandler(output);

CommandLine cl = CommandLine.parse(command);
cl.addArgument("-jar");
cl.addArgument(dataParserPath);

DefaultExecutor exec = new DefaultExecutor();
DataInputStream is = null;
try {
    is = new DataInputStream(new PipedInputStream(output));
    exec.setStreamHandler(psh);
    exec.execute(dataParserCommandLine);
} catch (ExecuteException ex) {
} catch (IOException ex) {
}

return is;
}

Answer 2

Below is some sample code for using Runtime.exec. it would be simple to adapt it to your use. From http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html?page=4

import java.util.*;
import java.io.*;
class StreamGobbler extends Thread
{
    InputStream is;
    String type;

    StreamGobbler(InputStream is, String type)
    {
        this.is = is;
        this.type = type;
    }

    public void run()
    {
        try
        {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
                System.out.println(type + ">" + line);    
            } catch (IOException ioe)
              {
                ioe.printStackTrace();  
              }
    }
}


public class GoodWindowsExec
{
    public static void main(String args[])
    {
        if (args.length < 1)
        {
            System.out.println("USAGE: java GoodWindowsExec <cmd>");
            System.exit(1);
        }

        try
        {            
            String osName = System.getProperty("os.name" );
            String[] cmd = new String[3];
            if( osName.equals( "Windows NT" ) )
            {
                cmd[0] = "cmd.exe" ;
                cmd[1] = "/C" ;
                cmd[2] = args[0];
            }
            else if( osName.equals( "Windows 95" ) )
            {
                cmd[0] = "command.com" ;
                cmd[1] = "/C" ;
                cmd[2] = args[0];
            }

            Runtime rt = Runtime.getRuntime();
            System.out.println("Execing " + cmd[0] + " " + cmd[1] 
                               + " " + cmd[2]);
            Process proc = rt.exec(cmd);
            // any error message?
            StreamGobbler errorGobbler = new 
                StreamGobbler(proc.getErrorStream(), "ERROR");            

            // any output?
            StreamGobbler outputGobbler = new 
                StreamGobbler(proc.getInputStream(), "OUTPUT");

            // kick them off
            errorGobbler.start();
            outputGobbler.start();

            // any error???
            int exitVal = proc.waitFor();
            System.out.println("ExitValue: " + exitVal);        
        } catch (Throwable t)
          {
            t.printStackTrace();
          }
    }
}

EDIT: This does not exactly answer the question, since it uses the JDK classes, but it works.

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