Get Command Prompt Output to String In Java

Question

I need a java method that will read command prompt output and store it into a String to be read into Java.

This is what I have so far but isn\'t working right.

Answer 1

First you need a non-blocking way to read from Standard.out and Standard.err

private class ProcessResultReader extends Thread
{
    final InputStream is;
    final String type;
    final StringBuilder sb;

    ProcessResultReader(@Nonnull final InputStream is, @Nonnull String type)
    {
        this.is = is;
        this.type = type;
        this.sb = new StringBuilder();
    }

    public void run()
    {
        try
        {
            final InputStreamReader isr = new InputStreamReader(is);
            final BufferedReader br = new BufferedReader(isr);
            String line = null;
            while ((line = br.readLine()) != null)
            {
                this.sb.append(line).append("\n");
            }
        }
        catch (final IOException ioe)
        {
            System.err.println(ioe.getMessage());
            throw new RuntimeException(ioe);
        }
    }

    @Override
    public String toString()
    {
        return this.sb.toString();
    }
}

Then you need to tie this class into the respective InputStream and OutputStreamobjects.

    try
    {
        final Process p = Runtime.getRuntime().exec(String.format("cmd /c %s", query));
        final ProcessResultReader stderr = new ProcessResultReader(p.getErrorStream(), "STDERR");
        final ProcessResultReader stdout = new ProcessResultReader(p.getInputStream(), "STDOUT");
        stderr.start();
        stdout.start();
        final int exitValue = p.waitFor();
        if (exitValue == 0)
        {
            System.out.print(stdout.toString());
        }
        else
        {
            System.err.print(stderr.toString());
        }
    }
    catch (final IOException e)
    {
        throw new RuntimeException(e);
    }
    catch (final InterruptedException e)
    {
        throw new RuntimeException(e);
    }

This is pretty much the boiler plate I use when I need to Runtime.exec() anything in Java.

A more advanced way would be to use FutureTask and Callable or at least Runnable rather than directly extending Thread which isn't the best practice.

NOTE:

The @Nonnull annotations are in the JSR305 library. If you are using Maven, and you are using Maven aren't you, just add this dependency to your pom.xml.

  com.google.code.findbugs
  jsr305
  1.3.9