Code Listener in java

CodeListener.java

package org.monkstone;

import java.nio.file.WatchEvent;

interface CodeListener {
    public void code_event(WatchEvent<?> event);     
}

CodeListenerTest.java

import java.nio.file.WatchEvent;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author tux
 */
public class CodeListenerTest {

    WatchSketchDir watcher;

    public CodeListenerTest() {
        try {
            watcher = WatchSketchDir.watch("/home/tux/test"); 
            watcher.addListener(new CodeListenerImpl());
        } catch (IOException ex) {
            Logger.getLogger(CodeListenerTest.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

    public class CodeListenerImpl implements CodeListener {

        @Override
        public void code_event(WatchEvent<?> event) {
            if (event.kind() == StandardWatchEventKinds.ENTRY_MODIFY) {
                System.out.println("bingo");
            }
        }
    }

    public static void main(String[] args) {
        CodeListenerTest test = new CodeListenerTest();

    }

}

WatchSketchDir.java

/**
 * This class allows JRubyArt to watch for changes to sketch files
 * specifically those with a 'rb' or 'glsl' extension requires user to supply
 * a path String and code listener to constructor. The code listener should 
 * accept a filesystem WatchEvent
 */

/*
 * This code is a modified version of WatchDir.java
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.monkstone;
import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import static java.nio.file.StandardWatchEventKinds.*;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.Map;

/**
 * Example to watch a directory (or tree) for changes to files.
 */
public class WatchSketchDir {

    private final WatchService watcher;
    private final Map<WatchKey, Path> keys;
    private boolean trace = false;
    static WatchSketchDir sketchWatcher;
    
    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>) event;
    }


    /**
     * Register the given directory with the WatchService
     */
    private void register(Path dir) throws IOException {
        WatchKey key = dir.register(watcher, ENTRY_MODIFY);
        if (trace) {
            Path prev = keys.get(key);
            if (prev == null) {
                System.out.format("register: %s\n", dir);
            } else if (!dir.equals(prev)) {
                System.out.format("update: %s -> %s\n", prev, dir);
            }
        }
        keys.put(key, dir);
    }

    /**
     * Register the given directory, and all its sub-directories, with the
     * WatchService.
     */
    private void registerAll(final Path start) throws IOException {
        // register directory and sub-directories
        Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
            @Override
            public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
                    throws IOException {
                register(dir);
                return FileVisitResult.CONTINUE;
            }
        });
    }
    
    static final WatchSketchDir watch(String dir) throws IOException{
        sketchWatcher = new WatchSketchDir(dir);
        return sketchWatcher;
    }

    /**
     * Creates a WatchService and registers the given directory
     * @param dir String
     * @param obj CodeListener
     * @throws IOException
     */
    private WatchSketchDir(String dir) throws IOException {
        this(Paths.get(dir));
    }

    /**
     * Creates a WatchService and registers the given directory
     *
     * @param dir Path
     * @param obj CodeListener
     * @throws java.io.IOException
     */
    private WatchSketchDir(Path dir) throws IOException {
        this.watcher = FileSystems.getDefault().newWatchService();
        this.keys = new HashMap<>();

        System.out.format("Scanning Codebase\n", dir);
        registerAll(dir);
        System.out.format("Watching %s\n", dir);

        // enable trace after initial registration
        this.trace = true;
    }

    /**
     * Process all events for keys queued to the watcher
     */
    void addListener(CodeListener obj) {
        for (;;) {

            // wait for key to be signalled
            WatchKey key;
            try {
                key = watcher.take();
            } catch (InterruptedException x) {
                return;
            }

            Path dir = keys.get(key);
            if (dir == null) {
                System.err.println("WatchKey not recognized!!");
                continue;
            }

            key.pollEvents().stream().forEach((WatchEvent<?> event) -> {
                WatchEvent.Kind kind = event.kind();
                // TBD - provide example of how OVERFLOW event is handled
                if (!(kind == OVERFLOW)) {
                    // Context for directory entry event is the file name of entry
                    WatchEvent<Path> ev = cast(event);
                    Path name = ev.context();
                    Path child = dir.resolve(name);
                    if (child.toFile().getAbsolutePath().endsWith(".rb")
                            || child.toFile().getAbsolutePath().endsWith(".glsl")) {
                        obj.code_event(event);
                    }
                    // if directory is created, and watching recursively, then
                    // register it and its sub-directories
                }
            });

            // reset key and remove from set if directory no longer accessible
            boolean valid = key.reset();
            if (!valid) {
                keys.remove(key);

                // all directories are inaccessible
                if (keys.isEmpty()) {
                    break;
                }
            }
        }
    }    
}