source: trunk/JavaHelperLib/src/de/ugoe/cs/util/console/CommandExecuter.java

package de.ugoe.cs.util.console;

import java.security.InvalidParameterException;
import java.util.ArrayList;
import java.util.List;

/**
 * <p>
 * Executes commands. The commands have to implement the {@link Command}
 * interface and be in packages registered using addCommandPackage().
 * Additionally, default commands are implemented in the
 * de.ugoe.cs.util.console.defaultcommands package.
 * </p>
 * <p>
 * This class is implemented as a <i>Singleton</i>.
 * </p>
 * 
 * @author Steffen Herbold
 * @version 1.0
 */
public class CommandExecuter {

        /**
         * <p>
         * Handle of the CommandExecuter instance.
         * </p>
         */
        private final static CommandExecuter theInstance = new CommandExecuter();

        /**
         * <p>
         * Prefix of all command classes.
         * </p>
         */
        private static final String cmdPrefix = "CMD";

        /**
         * <p>
         * Name of the package for default commands.
         * </p>
         */
        private static final String defaultPackage = "de.ugoe.cs.util.console.defaultcommands";

        /**
         * <p>
         * List of packages in which commands may be defined. The exec methods trys
         * to load command from these packages in the order they have been added.
         * </p>
         * <p>
         * The de.ugoe.cs.util.console.defaultcommands package has always lowest
         * priority, unless it is specifically added.
         * </p>
         */
        private List<String> commandPackageList;

        /**
         * <p>
         * Returns the instance of CommandExecuter. If no instances exists yet, a
         * new one is created.
         * </p>
         * 
         * @return the instance of CommandExecuter
         */
        public static synchronized CommandExecuter getInstance() {
                return theInstance;
        }

        /**
         * <p>
         * Creates a new CommandExecuter. Private to prevent multiple instances
         * (Singleton).
         * </p>
         */
        private CommandExecuter() {
                commandPackageList = new ArrayList<String>();
        }

        /**
         * <p>
         * Adds a package that will be used by {@link #exec(String)} to load command
         * from.
         * </p>
         * 
         * @param pkg
         *            package where commands are located
         * @throws InvalidParameterException
         *             thrown if the package name is null or empty string
         */
        public void addCommandPackage(String pkg) {
                if ("".equals(pkg) || pkg == null) {
                        throw new InvalidParameterException(
                                        "package name must not be null or empty string");
                }
                commandPackageList.add(pkg);
        }

        /**
         * <p>
         * Executes the command defined by string. A command has the following form
         * (mix of EBNF and natural language):
         * </p>
         * <code>
         * &lt;command&gt; := &lt;commandname&gt;&lt;whitespace&gt;{&lt;parameter&gt;}<br>
         * &lt;commandname&gt; := String without whitespaces. Has to be a valid Java class name<br>
         * &lt;parameter&gt; := &lt;string&gt;|&lt;stringarray&gt;<br>
         * &lt;string&gt; := &lt;stringwithoutwhitespaces&gt;|&lt;stringwithwhitespaces&gt;
         * &lt;stringwithoutwhitespaces&gt; := a string without whitespaces<br>
         * &lt;stringwithoutwhitespaces&gt; := a string, that can have whitespaces, but must be in double quotes<br>
         * &lt;stringarray&gt; := "["&lt;string&gt;{&lt;whitespace&gt;&lt;string&gt;"]"
         * </code>
         * 
         * @param command
         *            the command as a string
         */
        public void exec(String command) {
                Console.commandNotification(command);
                Command cmd = null;
                CommandParser parser = new CommandParser();
                parser.parse(command);
                for (int i = 0; cmd == null && i < commandPackageList.size(); i++) {
                        cmd = loadCMD(commandPackageList.get(i) + "." + cmdPrefix
                                        + parser.getCommandName());
                }
                if (cmd == null) { // check if command is available as default command
                        cmd = loadCMD(defaultPackage + "." + cmdPrefix
                                        + parser.getCommandName());
                }
                if (cmd == null) {
                        Console.println("Unknown command");
                } else {
                        try {
                                cmd.run(parser.getParameters());
                        } catch (InvalidParameterException e) {
                                cmd.help();
                        }
                }
        }

        /**
         * <p>
         * Helper method that loads a class and tries to cast it to {@link Command}.
         * </p>
         * 
         * @param className
         *            qualified name of the class (including package name)
         * @return if class is available and implement {@link Command} and instance
         *         of the class, null otherwise
         */
        private Command loadCMD(String className) {
                Command cmd = null;
                try {
                        Class<?> cmdClass = Class.forName(className);
                        cmd = (Command) cmdClass.newInstance();
                } catch (NoClassDefFoundError e) {
                        String[] splitResult = e.getMessage().split("CMD");
                        String correctName = splitResult[splitResult.length - 1].replace(
                                        ")", "");
                        Console.println("Did you mean " + correctName + "?");
                } catch (ClassNotFoundException e) {
                } catch (IllegalAccessException e) {
                } catch (InstantiationException e) {
                } catch (ClassCastException e) {
                        Console.traceln(className + "found, but does not implement Command");
                }
                return cmd;
        }
}