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A set of utilities for Java
There is a newer version: 3.0.0
package org.rx.io;

import lombok.*;
import lombok.extern.slf4j.Slf4j;
import org.rx.bean.FlagsEnum;
import org.rx.core.Delegate;
import org.rx.core.Disposable;
import org.rx.core.EventArgs;
import org.rx.core.EventTarget;
import org.rx.core.Tasks;

import java.nio.file.*;
import java.util.concurrent.Future;
import java.util.function.Predicate;

import static org.rx.core.App.*;
import static org.rx.core.Extends.quietly;

@Slf4j
public class FileWatcher extends Disposable implements EventTarget {
    @RequiredArgsConstructor
    public static class FileChangeEventArgs extends EventArgs {
        @Getter
        final Path path;
        final WatchEvent.Kind changeKind;

        public boolean isCreate() {
            return StandardWatchEventKinds.ENTRY_CREATE.equals(changeKind);
        }

        public boolean isModify() {
            return StandardWatchEventKinds.ENTRY_MODIFY.equals(changeKind);
        }

        public boolean isDelete() {
            return StandardWatchEventKinds.ENTRY_DELETE.equals(changeKind);
        }
    }

    public final Delegate onChanged = Delegate.create();
    @Getter
    private final String directoryPath;
    private final WatchService service;
    private final Future future;
    @Setter
    private Predicate filter;

    @Override
    public FlagsEnum eventFlags() {
        return EventFlags.QUIETLY.flags();
    }

    public FileWatcher(String directoryPath) {
        this(directoryPath, null);
    }

    @SneakyThrows
    public FileWatcher(String directoryPath, Predicate filter) {
        this.directoryPath = directoryPath;
        this.filter = filter;

        Files.createDirectory(directoryPath);
        service = FileSystems.getDefault().newWatchService();
        Paths.get(directoryPath).register(service, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.ENTRY_DELETE);

        future = Tasks.run(() -> {
            while (!isClosed()) {
                quietly(() -> {
                    WatchKey key = service.take();
                    for (WatchEvent event : key.pollEvents()) {
                        raiseEvent(event);
                    }
                    key.reset();
                });
            }
        });
    }

    @SneakyThrows
    @Override
    protected void freeObjects() {
        future.cancel(false);
        service.close();
    }

    private void raiseEvent(WatchEvent tmp) {
        WatchEvent event = (WatchEvent) tmp;
        Path absolutePath = Paths.get(directoryPath, event.context().toString());
        if (filter != null && !filter.test(absolutePath)) {
            return;
        }
        raiseEvent(onChanged, new FileChangeEventArgs(absolutePath, event.kind()));
    }
}