[main] FileBackedRef from Inceptum

src/main/java/io/gitlab/jfronny/commons/cache/FileBackedRef.java

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+package io.gitlab.jfronny.commons.cache;
+
+import io.gitlab.jfronny.commons.io.JFiles;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.lang.reflect.Type;
+import java.nio.file.*;
+
+/**
+ * Maintains an object reference backed by a file and re-creates it automatically upon change
+ * @param <T> The type of the referenced object
+ */
+public class FileBackedRef<T> implements Closeable {
+    private final Path filePath;
+    private final Type type;
+    private final WatchService service;
+    private T cache = null;
+
+    public FileBackedRef(Path filePath, Type type) throws IOException {
+        this.filePath = filePath;
+        this.type = type;
+        this.service = FileSystems.getDefault().newWatchService();
+        filePath.getParent().register(service, StandardWatchEventKinds.ENTRY_MODIFY);
+    }
+
+    public FileBackedRef(Path filePath, Class<T> type) throws IOException {
+        this(filePath, (Type) type);
+    }
+
+    public T get() throws IOException {
+        WatchKey key = service.poll();
+        boolean update = cache == null;
+        if (key != null) {
+            for (WatchEvent<?> event : key.pollEvents()) {
+                update |= event.context().equals(filePath);
+            }
+            key.reset();
+        }
+        if (update) cache = JFiles.readObject(filePath, type);
+        return cache;
+    }
+
+    @Override
+    public void close() throws IOException {
+        service.close();
+    }
+}