Why java hang when invoking WMIC command

Today I want to invoke WMIC command from java program (through Runtim

e.getRuntime().exec(.....)).


I use the following code, but unfortunately, my java appears to "deadlock".

public void testWMIC(){
	final String command = "cmd /c wmic.exe Process get processid /format:csv";
	ProcessExecutor executor = new ProcessExecutor(command, ProcessExecutor.class);
	executor.start();
	executor.waitFor(500);
}

I search many web sites, read the instructions about how to use Runtime.exec() in Java, but there was no hint for this issue.

Finally, I found a website, which said that sometimes the program invoked by command does NOT "Stop".

Although I feel it is ridiculous, I tried the following command. This time everything works OK.

final String command = "cmd /c wmic.exe Process get processid /format:csv <NUL";

Reference Code 1

Reference Code
import java.io.IOException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ProcessExecutor extends Thread {
	protected Logger _log;
	private String command;
	private Process child;
	private boolean isValidProcess = true;

	public ProcessExecutor(String command, Class logType) {
		_log = LoggerFactory.getLogger(logType);
		this.command = command;
	}

	public Process getChildProcess() {
		if ((child == null) || (isValidProcess)) {
			try {
				Thread.sleep(100);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		return child;
	}

	public void waitFor(long time) {
		long times = time / 100;
		while (isAlive()&&(times>0)) {
			try {
				Thread.sleep(100);
				times--;
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

	public void run() {
		child = null;
		isValidProcess = true;
		_log.info("New Invocation Command is {}", command);
		child = exec(command);
		if (child == null) {
			isValidProcess = false;
			return;
		}

		final StreamGlobber s1 = new StreamGlobber(_log,
				java.util.logging.Level.INFO, child.getInputStream());
		final StreamGlobber s2 = new StreamGlobber(_log,
				java.util.logging.Level.SEVERE, child.getErrorStream());
		s1.start();
		s2.start();

		try {
			if (child != null) {
				child.waitFor();
			}
		} catch (final InterruptedException e) {
			e.printStackTrace();
		}
	}

	private Process exec(String command) {
		Runtime run = Runtime.getRuntime();
		try {
			return run.exec(command);
		} catch (IOException e) {
			_log.error(e.getMessage());
			return null;
		}
	}
}

Reference Code 2

Reference Code
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.logging.Level;

import org.slf4j.Logger;


public class StreamGlobber implements Runnable {
	private Level _level;
	private InputStream _is;
	private Thread _thread;
	private Logger _log;
	private boolean alive;

	public StreamGlobber(final Logger log, final Level level,
			final InputStream is) {
		this._log = log;
		this._level = level;
		this._is = is;
	}

	public void start() {
		_thread = new Thread(this);
		alive = true;
		_thread.start();
	}
	
	public boolean isAlive(){
		return alive;
	}

	public void run() {
		try {
			InputStreamReader isr = new InputStreamReader(_is);
			BufferedReader br = new BufferedReader(isr);

			while (true) {
				String s = br.readLine();
				if (s == null)
					break;
				if (_level.equals(Level.SEVERE)) {
					this._log.error(s);
				} else {
					this._log.info(s);
				}
			}
			alive = false;
			_is.close();

		} catch (Exception ex) {
			_log.error(ex.getMessage(), ex);
		}
	}
}