Add trigger for the existence of files.

diff --git a/src/main/java/net/pterodactylus/reactor/triggers/FileExistenceTrigger.java b/src/main/java/net/pterodactylus/reactor/triggers/FileExistenceTrigger.java
new file mode 100644 (file)
index 0000000..2be86ea
--- /dev/null
+++ b/src/main/java/net/pterodactylus/reactor/triggers/FileExistenceTrigger.java
@@ -0,0 +1,42 @@
+/*
+ * Reactor - FileExistenceTrigger.java - Copyright © 2013 David Roden
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package net.pterodactylus.reactor.triggers;
+
+import net.pterodactylus.reactor.Trigger;
+import net.pterodactylus.reactor.states.FileState;
+
+/**
+ * A trigger that detects changes in the existence of a file.
+ *
+ * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
+ */
+public class FileExistenceTrigger implements Trigger<FileState> {
+
+       //
+       // TRIGGER METHODS
+       //
+
+       /**
+        * {@inheritDoc}
+        */
+       @Override
+       public boolean triggers(FileState previousState, FileState currentState) {
+               return previousState.exists() != currentState.exists();
+       }
+
+}