Interacting with Powershell from Java

Question

Hi,
I'm trying to run a Java application which creates a new powershell process on startup and then later on interacts with it multiple times. Calling powershell.exe and have it execute a single command and return the output works fine for me. The problem arises if I don't want the powershell process to immediately finish/exit but to stay open so I can write to its outputStream and receive results back from the inputStream.
String input = "dir";
String[] commandList = {"powershell.exe", "-Command", "dir"};
ProcessBuilder pb = new ProcessBuilder(commandList);
Process p = pb.start();
if(input != null) { 
PrintWriter writer = new PrintWriter(new OutputStreamWriter(new BufferedOutputStream(p.getOutputStream())), true);
writer.println(input);
writer.flush();
writer.close();
//p.getOutputStream().close();
Gobbler outGobbler = new Gobbler(p.getInputStream());
Gobbler errGobbler = new Gobbler(p.getErrorStream());
Thread outThread = new Thread(outGobbler);
Thread errThread = new Thread(errGobbler);
outThread.start();
errThread.start();
System.out.println("Waiting for the Gobbler threads to join...");
outThread.join();
errThread.join();
System.out.println("Waiting for the process to exit...");
int exitVal = p.waitFor();
System.out.println("\n****************************");
System.out.println("Command: " + "cmd.exe /c dir");
System.out.println("Exit Value = " + exitVal);
List<String> output = outGobbler.getOuput();
input = "";
for(String o: output) { 
input += o;
System.out.println("Final Output:");
System.out.println(input);
This code returns the result of the "dir" command from a powershell - fine. But as you can see, I'm trying to run a second "dir" command using
PrintWriter writer = new PrintWriter(new OutputStreamWriter(new BufferedOutputStream(p.getOutputStream())), true);
writer.println(input);
writer.flush();
This has no effect whatsoever - no second dir output is shown when I run my code. I've also experimented with a powershell.exe option to open the powershell but not close it immediately:
String[] commandList = {"powershell.exe", "-NoExit", "-Command", "dir"};
But then my code hangs, meaning the Gobbler's who consume the process's inputStream don't read anything - strangely enough: they don't even read the first line - there must be at least some output....
I've also tried to close the process's outputStream after writing the second "dir" command to it - didn't change anything.
But when I initially call the cmd.exe using the /k (keep open) switch:
String[] commandList = {"cmd.exe", "/k", "dir"};
I can then still write to that outputstream and invoke the second "dir" command and get the output of both "dir" commands from the inputstream fo that process.
Any help is highly appreciated.
Thanks
Kurt

Answer 1

user4491593 wrote:
BUT: my Gobblers only read the output of all my commands Then why don't change your Gobbler code ? ;)
Test this, it's ugly and needs improvemens, but by now works fine on linux and windows:
public class Gobbler implements Runnable {
    private PrintStream out;
    private String message;
    private BufferedReader reader;
    public Gobbler(InputStream inputStream, PrintStream out) {
        this.reader = new BufferedReader(new InputStreamReader(inputStream));
               this.out = out;
        this.message = ( null != message ) ? message : "";
    public void run() {
        String line;
        try {
            while (null != (line = this.reader.readLine())) {
                out.println(message + line);
            this.reader.close();
        } catch (IOException e) {
            System.err.println("ERROR: " + e.getMessage());
public class PowerConsole {
    private ProcessBuilder pb;
    Process p;
    boolean closed = false;
    PrintWriter writer;
    PowerConsole(String[] commandList) {
        pb = new ProcessBuilder(commandList);
        try {
            p = pb.start();
        } catch (IOException ex) {
            throw new RuntimeException("Cannot execute PowerShell.exe", ex);
        writer = new PrintWriter(new OutputStreamWriter(new BufferedOutputStream(p.getOutputStream())), true);
        Gobbler outGobbler = new Gobbler(p.getInputStream(), System.out);
        Gobbler errGobbler = new Gobbler(p.getErrorStream(), System.out);
        Thread outThread = new Thread(outGobbler);
        Thread errThread = new Thread(errGobbler);
        outThread.start();
        errThread.start();
    public void execute(String command) {
        if (!closed) {
            writer.println(command);
            writer.flush();
        } else {
            throw new IllegalStateException("Power console has ben closed.");
    public void close() {
        try {
            execute("exit");
            p.waitFor();
        } catch (InterruptedException ex) {
    public static void main(String[] args) throws IOException, InterruptedException {
        /*   PowerConsole pc = new PowerConsole(new String[]{"/bin/bash"});
        PowerConsole pc = new PowerConsole(new String[]{"/bin/bash"});
        pc.execute("pwd");
        pc.execute("ls");
        pc.execute("cd /");
        pc.execute("ls -l");
        pc.execute("cd ~");
        pc.execute("find . -name 'test.*' -print");
        pc.close();
        //      PowerConsole pc = new PowerConsole(new String[]{"cmd.exe"});
        PowerConsole pc = new PowerConsole(new String[]{"powershell.exe", "-NoExit", "-Command", "-"});
        System.out.println("========== Executing dir");
        pc.execute("dir");
        System.out.println("========== Executing cd\\");
        pc.execute("cd \\"); Thread.sleep(2000);
        System.out.println("========== Executing dir");
        pc.execute("dir"); Thread.sleep(2000);
        System.out.println("========== Executing cd \\temp");
        pc.execute("cd \\temp"); Thread.sleep(2000);
        System.out.println("========== Executing dir");
        pc.execute("dir"); Thread.sleep(2000);
        System.out.println("========== Executing cd \\bubba");
        pc.execute("cd \\bubba"); Thread.sleep(2000);
        System.out.println("========== Exiting .... bye.");
        pc.close();
}I tested this and there is still a little problem -look at the test below.
It seems that when thecommand
executed in the powershell prints only a one ot two lines,
powershell doesn't flush the output stream
.... but this rather problem of powershell, not the java code
I have not a clue how to force powershell to flush
it's output stream after each command.
C:\temp>java -jar PowerShell.jar
========== Executing dir
    Directory: Microsoft.PowerShell.Core\FileSystem::C:\temp
Mode                LastWriteTime     Length Name
-a---        2012-01-09     01:16       5290 PowerShell.jar
========== Executing cd\
========== Executing dir
    Directory: Microsoft.PowerShell.Core\FileSystem::C:\
Mode                LastWriteTime     Length Name
d----        2012-01-08     02:56            61587b977687a6e22fbe
d----        2011-12-14     03:19            Documents and Settings
d----        2011-12-15     00:05            oraclexe
d-r--        2012-01-08     03:44            Program Files
d----        2012-01-05     19:59            sqldeveloper
d----        2012-01-09     01:15            temp
d----        2012-01-09     01:13            WINDOWS
-a---        2011-12-14     03:12          0 AUTOEXEC.BAT
-a---        2011-12-14     03:12          0 CONFIG.SYS
========== Executing cd \temp
========== Executing dir
    Directory: Microsoft.PowerShell.Core\FileSystem::C:\temp
Mode                LastWriteTime     Length Name
-a---        2012-01-09     01:16       5290 PowerShell.jar
========== Executing cd \bubba
Set-Location : Cannot find path 'C:\bubba' because it does not exist.
At line:1 char:3
+ cd  <<<< \bubba
========== Exiting .... bye.
C:\temp>