Added convenience overload

Author: DavyLandman

src/main/java/engineering/swat/watch/WatchEventListener.java

@@ -0,0 +1,37 @@
+/*
+ * BSD 2-Clause License
+ *
+ * Copyright (c) 2023, Swat.engineering
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. 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.
+ *
+ * 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 HOLDER 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 engineering.swat.watch;
+
+/**
+ * A visit like interface that allows you to only override the functions you are interested in
+ */
+public interface WatchEventListener {
+    default void onCreated(WatchEvent ev) { }
+    default void onModified(WatchEvent ev) { }
+    default void onDeleted(WatchEvent ev) { }
+    default void onOverflow(WatchEvent ev) { }
+}

src/main/java/engineering/swat/watch/Watcher.java

@@ -100,10 +100,41 @@ public static Watcher watch(Path path, WatchScope scope) {
      * @return this for optional method chaining
      */
     public Watcher on(Consumer<WatchEvent> eventHandler) {
+        if (this.eventHandler != NULL_HANDLER) {
+            throw new IllegalArgumentException("on handler cannot be set more than once");
+        }
         this.eventHandler = eventHandler;
         return this;
     }
 
+    /**
+     * Convenience variant of {@link #on(Consumer)}, which allows you to only respond to certain events
+     */
+    public Watcher on(WatchEventListener listener) {
+        if (this.eventHandler != NULL_HANDLER) {
+            throw new IllegalArgumentException("on handler cannot be set more than once");
+        }
+        this.eventHandler = ev -> {
+            switch (ev.getKind()) {
+                case CREATED:
+                    listener.onCreated(ev);
+                    break;
+                case DELETED:
+                    listener.onDeleted(ev);
+                    break;
+                case MODIFIED:
+                    listener.onModified(ev);
+                    break;
+                case OVERFLOW:
+                    listener.onOverflow(ev);
+                    break;
+                default:
+                    throw new IllegalArgumentException("Unexpected kind: " + ev.getKind());
+            }
+        };
+        return this;
+    }
+
     /**
      * Optionally configure the executor in which the {@link #on(Consumer)} callbacks are scheduled.
      * If not defined, every task will be scheduled on the {@link java.util.concurrent.ForkJoinPool#commonPool()}.