Addd a new utility for a persisted boolean

core/src/main/java/jenkins/util/io/FileBoolean.java

+package jenkins.util.io;
+
+import jenkins.model.Jenkins;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Uses a presence/absence of a file as a persisted boolean storage.
+ *
+ * <p>
+ * This is convenient when you need to store just a few bits of infrequently accessed information
+ * as you can forget the explicit persistence of it. This class masks I/O problem, so if the persistence
+ * fails, you'll get no error report.
+ *
+ * @author Kohsuke Kawaguchi
+ * @since 1.498
+ */
+public class FileBoolean {
+    private final File file;
+
+    public FileBoolean(File file) {
+        this.file = file;
+    }
+
+    public FileBoolean(Class owner, String name) {
+        this(new File(Jenkins.getInstance().getRootDir(),owner.getName().replace('$','.')+'/'+name));
+    }
+
+    /**
+     * Gets the current state. True if the file exists, false if it doesn't.
+     */
+    public boolean get() {
+        return file.exists();
+    }
+
+    public boolean isOn() { return get(); }
+    public boolean isOff() { return !get(); }
+
+    public void set(boolean b) {
+        if (b) on(); else off();
+    }
+
+    public void on() {
+        try {
+            file.getParentFile().mkdirs();
+            new FileOutputStream(file).close();
+        } catch (IOException e) {
+            LOGGER.log(Level.WARNING, "Failed to touch "+file);
+        }
+    }
+
+    public void off() {
+        file.delete();
+    }
+
+    private static final Logger LOGGER = Logger.getLogger(FileBoolean.class.getName());
+}