net_alchim31_livereload.Watcher Maven / Gradle / Ivy

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package net_alchim31_livereload;

import static java.nio.file.LinkOption.NOFOLLOW_LINKS;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;

import java.io.IOException;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.SimpleFileVisitor;
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;

/**
 * @see http://docs.oracle.com/javase/tutorial/essential/io/notification.html
 * @author dwayne
 * 
 */
//TODO make a start/stop/join method
public class Watcher {
  private final WatchService        _watcher;
  private final Map _keys;
  private final Path                _docroot;
  
  public LRWebSocketHandler         listener = null;

  public Watcher(Path docroot) throws Exception {
    _docroot = docroot;
    this._watcher = docroot.getFileSystem().newWatchService();
    this._keys = new HashMap();

    //System.out.format("Scanning %s ...\n", _docroot);
    registerAll(_docroot);
    //System.out.println("Done.");
  }

  private void notify(String path) throws Exception {
    LRWebSocketHandler l = listener;
    if (l != null)
      l.notifyChange(path);
  }

  @SuppressWarnings("unchecked")
  static  WatchEvent cast(WatchEvent event) {
    return (WatchEvent) event;
  }

  /**
   * Register the given directory with the WatchService
   */
  private void register(Path dir) throws IOException {
    WatchKey key = dir.register(_watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
    _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() {
      @Override
      public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
          throws IOException
      {
        register(dir);
        return FileVisitResult.CONTINUE;
      }
    });
  }

  /**
   * Process all events for keys queued to the watcher
   * @throws Exception 
   */
  void run() throws Exception {
    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;
      }

      for (WatchEvent event : key.pollEvents()) {
        WatchEvent.Kind kind = event.kind();

        // TBD - provide example of how OVERFLOW event is handled
        if (kind == OVERFLOW) {
          continue;
        }

        // Context for directory entry event is the file name of entry
        WatchEvent ev = cast(event);
        Path name = ev.context();
        Path child = dir.resolve(name);

        //System.out.format("%s: %s ++ %s\n", event.kind().name(), name, _docroot.relativize(child));
        if (kind == ENTRY_MODIFY) {
          notify(_docroot.relativize(child).toString());
        } else if (kind == ENTRY_CREATE) {
          // if directory is created, and watching recursively, then
          // register it and its sub-directories
          if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
            registerAll(child);
          }
        }
      }

      // 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;
        }
      }
    }
  }
}