Bullet-proof Java process runner

Last year I wrote a post about Validating WS-BPEL programmatically. I used external Apache ODE bpelc tool, but I invoked it using Java's ProcessBuilder and Process classes.

A friend of mine, Tomek, warned me about problem I might come across by not reading error and input streams.

He was right, some time ago while working on Nuntius 0.5 I wrote an integration test whose goal was to detect WS-BPEL errors. The error output generated by bpelc was so large that my process blocked itself and waited for the error stream to be read.

Today I present a bullet-proof version of my process runner. You can easily refactor this class to run any command line tools from Java.

ProcessBuilder

No comments, just the source code. Note the private InputStreamReaderThread class which I use for reading both error and input streams:

public class BPELCRunner {
 private static final Log log = LogFactory.getLog(BPELCRunner.class);
 private ProcessBuilder pb;
 private String message;
 public BPELCRunner(String command, String bpel) {
  pb = new ProcessBuilder(command, bpel);
 }
 public boolean compile() {
  Process p = null;
  try {
   p = pb.start();
   InputStreamReaderThread errorReader = new InputStreamReaderThread(p.getErrorStream());
   errorReader.start();
   InputStreamReaderThread inputReader = new InputStreamReaderThread(p.getInputStream());
   inputReader.start();
   p.waitFor();
   if (errorReader.getInput() != null) {
    message = errorReader.getInput();
    return false;
   }
  } catch (Throwable t) {
   log.error("Could not validate WS-BPEL process", t);
   message = "Error occurred while validating WS-BPEL process";
   return false;
  }
  return true;
 }
 public String getMessage() {
  return message;
 }
 public void setMessage(String message) {
  this.message = message;
 }
 private class InputStreamReaderThread extends Thread {
  private InputStream is;
  private String input;
  public ThreadInputStreamReader(InputStream is) {
   this.is = is;
  }
  @Override
  public void run() {
   try {
    byte[] output = IOUtils.toByteArray(is);
    input = new String(output);
   } catch (Exception e) {
    throw new RuntimeException(e);
   }
  }  
  public String getInput() {
   return input;
  }
 } 
}

I hope this simple class saves you a lot of time :)

Cheers,
Łukasz