segregate MethodHandles code from aggregation logic to make it easier…

… to delete when increasing the language level

src/main/java/com/timgroup/statsd/MapUtils.java

@@ -0,0 +1,51 @@
+package com.timgroup.statsd;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.util.Map;
+
+/**
+ * MethodHandle based bridge for using JDK8+ functionality at JDK7 language level.
+ * Can be removed when support for JDK7 is dropped.
+ */
+public class MapUtils {
+
+    private static final MethodHandle MAP_PUT_IF_ABSENT = buildMapPutIfAbsent();
+    /**
+     * Emulates {@code Map.putIfAbsent} semantics. Replace when baselining at JDK8+.
+     * @return the previous value associated with the message, or null if the value was not seen before
+     */
+    static Message putIfAbsent(Map<Message, Message> map, Message message) {
+        if (MAP_PUT_IF_ABSENT != null) {
+            try {
+                return (Message) (Object) MAP_PUT_IF_ABSENT.invokeExact(map, (Object) message, (Object) message);
+            } catch (Throwable ignore) {
+                return putIfAbsentFallback(map, message);
+            }
+        }
+        return putIfAbsentFallback(map, message);
+    }
+
+    /**
+     * Emulates {@code Map.putIfAbsent} semantics. Replace when baselining at JDK8+.
+     * @return the previous value associated with the message, or null if the value was not seen before
+     */
+    private static Message putIfAbsentFallback(Map<Message, Message> map, Message message) {
+        if (map.containsKey(message)) {
+            return map.get(message);
+        }
+        map.put(message, message);
+        return null;
+    }
+
+    private static MethodHandle buildMapPutIfAbsent() {
+        try {
+            return MethodHandles.publicLookup()
+                    .findVirtual(Map.class, "putIfAbsent",
+                            MethodType.methodType(Object.class, Object.class, Object.class));
+        } catch (Throwable ignore) {
+            return null;
+        }
+    }
+}

src/main/java/com/timgroup/statsd/StatsDAggregator.java

@@ -1,8 +1,5 @@
 package com.timgroup.statsd;
 
-import java.lang.invoke.MethodHandle;
-import java.lang.invoke.MethodHandles;
-import java.lang.invoke.MethodType;
 import java.util.ArrayList;
 import java.util.EnumSet;
 import java.util.HashMap;
@@ -18,8 +15,6 @@ public class StatsDAggregator {
     public static int DEFAULT_SHARDS = 4;  // 4 partitions to reduce contention.
 
     protected final String AGGREGATOR_THREAD_NAME = "statsd-aggregator-thread";
-
-    private static final MethodHandle MAP_PUT_IF_ABSENT = buildMapPutIfAbsent();
     protected static final Set<Message.Type> AGGREGATE_SET = EnumSet.of(Message.Type.COUNT, Message.Type.GAUGE,
             Message.Type.SET);
     protected final ArrayList<Map<Message, Message>> aggregateMetrics;
@@ -109,7 +104,7 @@ public boolean aggregateMessage(Message message) {
 
         synchronized (map) {
             // For now let's just put the message in the map
-            Message msg = putIfAbsent(map, message);
+            Message msg = MapUtils.putIfAbsent(map, message);
             if (msg != null) {
                 msg.aggregate(message);
                 if (telemetry != null) {
@@ -163,41 +158,4 @@ protected void flush() {
             }
         }
     }
-
-    /**
-     * Emulates {@code Map.putIfAbsent} semantics. Replace when baselining at JDK8+.
-     * @return the previous value associated with the message, or null if the value was not seen before
-     */
-    private static Message putIfAbsent(Map<Message, Message> map, Message message) {
-        if (MAP_PUT_IF_ABSENT != null) {
-            try {
-                return (Message) (Object) MAP_PUT_IF_ABSENT.invokeExact(map, (Object) message, (Object) message);
-            } catch (Throwable ignore) {
-                return putIfAbsentFallback(map, message);
-            }
-        }
-        return putIfAbsentFallback(map, message);
-    }
-
-    /**
-     * Emulates {@code Map.putIfAbsent} semantics. Replace when baselining at JDK8+.
-     * @return the previous value associated with the message, or null if the value was not seen before
-     */
-    private static Message putIfAbsentFallback(Map<Message, Message> map, Message message) {
-        if (map.containsKey(message)) {
-            return map.get(message);
-        }
-        map.put(message, message);
-        return null;
-    }
-
-    private static MethodHandle buildMapPutIfAbsent() {
-        try {
-            return MethodHandles.publicLookup()
-                    .findVirtual(Map.class, "putIfAbsent",
-                            MethodType.methodType(Object.class, Object.class, Object.class));
-        } catch (Throwable ignore) {
-            return null;
-        }
-    }
 }