Fix memory leak (#666)

Let maps implement Closeable.

Author: dr0i

metamorph-api/src/main/java/org/metafacture/metamorph/api/helpers/AbstractReadOnlyMap.java

@@ -16,6 +16,7 @@
 
 package org.metafacture.metamorph.api.helpers;
 
+import java.io.Closeable;
 import java.util.Collection;
 import java.util.Map;
 import java.util.Set;
@@ -29,7 +30,7 @@
  * @param <V> type of values
  * @author Markus Michael Geipel
  */
-public abstract class AbstractReadOnlyMap<K, V> implements Map<K, V> {
+public abstract class AbstractReadOnlyMap<K, V> implements Map<K, V>, Closeable {
 
     @Override
     public final int size() {

metamorph/src/main/java/org/metafacture/metamorph/maps/FileMap.java

@@ -290,4 +290,9 @@ public Set<String> keySet() {
         return Collections.unmodifiableSet(map.keySet());
     }
 
+    @Override
+    public void close() throws IOException {
+        map.clear();
+        fileOpener.closeStream();
+    }
 }

metamorph/src/main/java/org/metafacture/metamorph/maps/RestMap.java

@@ -107,4 +107,8 @@ public void setCharsetName(final String name) {
         charsetName = name;
     }
 
+    @Override
+    public void close() throws IOException {
+
+    }
 }