java实时监控文件行尾内容的实现

tail -f

  public interface Listener {

  /**
   * 发生文件变动事件时的处理逻辑
   * 
   * @param event
   */
  void fire(FileChangeEvent event);
}

public class FileChangeListener implements Listener {

  /**
   * 保存路径跟文件包装类的映射
   */
  private final Map<String, FileWrapper> map = new ConcurrentHashMap<>();

  public void fire(FileChangeEvent event) {
    switch (event.getKind().name()) {
    case "ENTRY_MODIFY":
      // 文件修改事件
      modify(event.getPath());
      break;
    default:
      throw new UnsupportedOperationException(
          String.format("The kind [%s] is unsupport.", event.getKind().name()));
    }
  }

  private void modify(Path path) {
    // 根据全路径获取包装类对象
    FileWrapper wrapper = map.get(path.toString());
    if (wrapper == null) {
      wrapper = new FileWrapper(path.toFile());
      map.put(path.toString(), wrapper);
    }
    try {
      // 读取追加的内容
      new ContentReader(wrapper).read();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

}

public class FileWrapper {

  /**
   * 当前文件读取的行数
   */
  private int currentLine;

  /**
   * 监听的文件
   */
  private final File file;

  public FileWrapper(File file) {
    this(file, 0);
  }

  public FileWrapper(File file, int currentLine) {
    this.file = file;
    this.currentLine = currentLine;
  }

  public int getCurrentLine() {
    return currentLine;
  }

  public void setCurrentLine(int currentLine) {
    this.currentLine = currentLine;
  }

  public File getFile() {
    return file;
  }

}

public class FileChangeEvent {

  /**
   * 文件全路径
   */
  private final Path path;
  /**
   * 事件类型
   */
  private final WatchEvent.Kind<?> kind;

  public FileChangeEvent(Path path, Kind<?> kind) {
    this.path = path;
    this.kind = kind;
  }

  public Path getPath() {
    return this.path;
  }

  public WatchEvent.Kind<?> getKind() {
    return this.kind;
  }

}

public class ContentReader {

  private final FileWrapper wrapper;

  public ContentReader(FileWrapper wrapper) {
    this.wrapper = wrapper;
  }

  public void read() throws FileNotFoundException, IOException {
    try (LineNumberReader lineReader = new LineNumberReader(new FileReader(wrapper.getFile()))) {
      List<String> contents = lineReader.lines().collect(Collectors.toList());
      if (contents.size() > wrapper.getCurrentLine()) {
        for (int i = wrapper.getCurrentLine(); i < contents.size(); i++) {
          // 这里只是简单打印出新加的内容到控制台
          System.out.println(contents.get(i));
        }
      }
      // 保存当前读取到的行数
      wrapper.setCurrentLine(contents.size());
    }
  }

}

public class DirectoryTargetMonitor {

  private WatchService watchService;

  private final FileChangeListener listener;

  private final Path path;

  private volatile boolean start = false;

  public DirectoryTargetMonitor(final FileChangeListener listener, final String targetPath) {
    this(listener, targetPath, "");
  }

  public DirectoryTargetMonitor(final FileChangeListener listener, final String targetPath, final String... morePaths) {
    this.listener = listener;
    this.path = Paths.get(targetPath, morePaths);
  }

  public void startMonitor() throws IOException {
    this.watchService = FileSystems.getDefault().newWatchService();
    // 注册变更事件到WatchService
    this.path.register(watchService, StandardWatchEventKinds.ENTRY_MODIFY);
    this.start = true;
    while (start) {
      WatchKey watchKey = null;
      try {
        // 阻塞直到有事件发生
        watchKey = watchService.take();
        watchKey.pollEvents().forEach(event -> {
          WatchEvent.Kind<?> kind = event.kind();
          Path path = (Path) event.context();
          Path child = this.path.resolve(path);
          listener.fire(new FileChangeEvent(child, kind));
        });
      } catch (Exception e) {
        this.start = false;
      } finally {
        if (watchKey != null) {
          watchKey.reset();
        }
      }
    }
  }

  public void stopMonitor() throws IOException {
    System.out.printf("The directory [%s] monitor will be stop ...\n", path);
    Thread.currentThread().interrupt();
    this.start = false;
    this.watchService.close();
    System.out.printf("The directory [%s] monitor will be stop done.\n", path);
  }

}

  public static void main(String[] args) throws IOException {
    DirectoryTargetMonitor monitor = new DirectoryTargetMonitor(new FileChangeListener(), "D:\\monitor");
    monitor.startMonitor();
  }