centralize ObjectCache into core templating API

adapters-api/src/main/java/io/nosqlbench/engine/api/templating/ObjectCache.java

@@ -0,0 +1,27 @@
+package io.nosqlbench.engine.api.templating;
+
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
+
+/**
+ * An object cache to memoize returned objects into a concurrent hash map by name.
+ * This is meant to be used when you want to lazily initialize an instance of something
+ * by name that is likely to be re-used over the lifetime of an owning object.
+ *
+ * @param <T> The type of object.
+ */
+public class ObjectCache<T> implements Function<String,T> {
+
+    private final ConcurrentHashMap<String,T> cache = new ConcurrentHashMap<>();
+
+    private final Function<String, T> newInstanceFunction;
+
+    public ObjectCache(Function<String,T> newInstanceFunction) {
+        this.newInstanceFunction = newInstanceFunction;
+    }
+
+    @Override
+    public T apply(String name) {
+        return cache.computeIfAbsent(name, newInstanceFunction);
+    }
+}