SystemCommandExecutor.java

// $Id: SystemCommandExecutor.java,v 1.1 2010/10/13 21:12:16 cmzmasek Exp $
/**
 * This class can be used to execute a system command from a Java application.
 * See the documentation for the public methods of this class for more
 * information.
 * 
 * Documentation for this class is available at this URL:
 * 
 * http://devdaily.com/java/java-processbuilder-process-system-exec
 * 
 * 
 * Copyright 2010 alvin j. alexander, devdaily.com.
 * 
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Lesser Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 * 
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser Public License along with
 * this program. If not, see <http://www.gnu.org/licenses/>.
 * 
 * Please ee the following page for the LGPL license:
 * http://www.gnu.org/licenses/lgpl.txt
 * 
 */

package org.forester.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.List;

public class SystemCommandExecutor {

    private final List<String>    commandInformation;
    private final String          adminPassword;
    private ThreadedStreamHandler inputStreamHandler;
    private ThreadedStreamHandler errorStreamHandler;

    /**
     * Pass in the system command you want to run as a List of Strings, as shown here:
     * 
     * List<String> commands = new ArrayList<String>();
     * commands.add("/sbin/ping");
     * commands.add("-c");
     * commands.add("5");
     * commands.add("www.google.com");
     * SystemCommandExecutor commandExecutor = new SystemCommandExecutor(commands);
     * commandExecutor.executeCommand();
     * 
     * Note: I've removed the other constructor that was here to support executing
     *       the sudo command. I'll add that back in when I get the sudo command
     *       working to the point where it won't hang when the given password is
     *       wrong.
     *
     * @param commandInformation The command you want to run.
     */
    public SystemCommandExecutor( final List<String> commandInformation ) {
        if ( commandInformation == null ) {
            throw new NullPointerException( "The commandInformation is required." );
        }
        this.commandInformation = commandInformation;
        adminPassword = null;
    }

    public int executeCommand() throws IOException, InterruptedException {
        int exitValue = -99;
        try {
            final ProcessBuilder pb = new ProcessBuilder( commandInformation );
            final Process process = pb.start();
            // you need this if you're going to write something to the command's input stream
            // (such as when invoking the 'sudo' command, and it prompts you for a password).
            final OutputStream stdOutput = process.getOutputStream();
            // i'm currently doing these on a separate line here in case i need to set them to null
            // to get the threads to stop.
            // see http://java.sun.com/j2se/1.5.0/docs/guide/misc/threadPrimitiveDeprecation.html
            final InputStream inputStream = process.getInputStream();
            final InputStream errorStream = process.getErrorStream();
            // these need to run as java threads to get the standard output and error from the command.
            // the inputstream handler gets a reference to our stdOutput in case we need to write
            // something to it, such as with the sudo command
            inputStreamHandler = new ThreadedStreamHandler( inputStream, stdOutput, adminPassword );
            errorStreamHandler = new ThreadedStreamHandler( errorStream );
            // TODO the inputStreamHandler has a nasty side-effect of hanging if the given password is wrong; fix it
            inputStreamHandler.start();
            errorStreamHandler.start();
            // TODO a better way to do this?
            exitValue = process.waitFor();
            // TODO a better way to do this?
            inputStreamHandler.interrupt();
            errorStreamHandler.interrupt();
            inputStreamHandler.join();
            errorStreamHandler.join();
        }
        catch ( final IOException e ) {
            // TODO deal with this here, or just throw it?
            throw e;
        }
        catch ( final InterruptedException e ) {
            // generated by process.waitFor() call
            // TODO deal with this here, or just throw it?
            throw e;
        }
        finally {
            return exitValue;
        }
    }

    /**
     * Get the standard error (stderr) from the command you just exec'd.
     */
    public StringBuilder getStandardErrorFromCommand() {
        return errorStreamHandler.getOutputBuffer();
    }

    /**
     * Get the standard output (stdout) from the command you just exec'd.
     */
    public StringBuilder getStandardOutputFromCommand() {
        return inputStreamHandler.getOutputBuffer();
    }
}