Implement DirectoryEvent Flow.Publisher and Flow.Subscriber

Consumers can asynchronously subscribe to directory events with the Flow components.

Ref: bisq-network#1798

common/src/main/java/bisq/common/io_watcher/DirectoryEventPublisher.java

@@ -0,0 +1,42 @@
+/*
+ * This file is part of Bisq.
+ *
+ * Bisq is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Bisq is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Bisq. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package bisq.common.io_watcher;
+
+import java.nio.file.Path;
+import java.nio.file.WatchEvent;
+import java.nio.file.WatchService;
+import java.util.Set;
+import java.util.concurrent.Flow;
+
+public class DirectoryEventPublisher implements Flow.Publisher<Path> {
+    private final WatchService watchService;
+    private final Path directoryPath;
+    private final Set<WatchEvent.Kind<?>> watchEventKinds;
+
+    public DirectoryEventPublisher(WatchService watchService, Path directoryPath, Set<WatchEvent.Kind<?>> watchEventKinds) {
+        this.watchService = watchService;
+        this.directoryPath = directoryPath;
+        this.watchEventKinds = watchEventKinds;
+    }
+
+    @Override
+    public void subscribe(Flow.Subscriber<? super Path> subscriber) {
+        var subscription = new DirectoryEventSubscription(subscriber, watchService, directoryPath, watchEventKinds);
+        subscriber.onSubscribe(subscription);
+    }
+}

common/src/main/java/bisq/common/io_watcher/DirectoryEventSubscriber.java

@@ -0,0 +1,53 @@
+/*
+ * This file is part of Bisq.
+ *
+ * Bisq is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Bisq is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Bisq. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package bisq.common.io_watcher;
+
+import java.nio.file.Path;
+import java.util.concurrent.Flow;
+import java.util.function.Consumer;
+
+public class DirectoryEventSubscriber implements Flow.Subscriber<Path> {
+    private final Consumer<? super Path> consumer;
+    private Flow.Subscription subscription;
+
+    public DirectoryEventSubscriber(Consumer<? super Path> consumer) {
+        this.consumer = consumer;
+    }
+
+    @Override
+    public void onSubscribe(Flow.Subscription subscription) {
+        this.subscription = subscription;
+        subscription.request(1);
+    }
+
+    @Override
+    public void onNext(Path path) {
+        consumer.accept(path);
+        subscription.request(1);
+    }
+
+    @Override
+    public void onError(Throwable throwable) {
+        throw new RuntimeException(throwable);
+    }
+
+    @Override
+    public void onComplete() {
+        throw new UnsupportedOperationException();
+    }
+}