make IdentityExtractionFn singleton

processing/src/main/java/io/druid/query/extraction/IdentityExtractionFn.java

@@ -24,6 +24,14 @@ import com.google.common.base.Strings;
 public class IdentityExtractionFn implements ExtractionFn
 {
   private static final byte CACHE_TYPE_ID = 0x6;
+
+  private static final IdentityExtractionFn instance = new IdentityExtractionFn();
+
+  private IdentityExtractionFn()
+  {
+
+  }
+
   @Override
   public byte[] getCacheKey()
   {
@@ -71,4 +79,9 @@ public class IdentityExtractionFn implements ExtractionFn
   {
      return o != null && o instanceof IdentityExtractionFn;
   }
+
+  public static final IdentityExtractionFn getInstance()
+  {
+    return instance;
+  }
 }

processing/src/main/java/io/druid/query/groupby/having/DimensionSelectorHavingSpec.java

@@ -48,11 +48,7 @@ public class DimensionSelectorHavingSpec implements HavingSpec
   {
     dimension = Preconditions.checkNotNull(dimName, "Must have attribute 'dimension'");
     this.value = value;
-    if (extractionFn != null) {
-      this.extractionFn = extractionFn;
-    } else {
-      this.extractionFn = new IdentityExtractionFn(); 
-    }
+    this.extractionFn = extractionFn != null ? extractionFn : IdentityExtractionFn.getInstance();
   }
 
   @JsonProperty("value")

processing/src/main/java/io/druid/query/search/SearchQueryRunner.java

@@ -121,7 +121,7 @@ public class SearchQueryRunner implements QueryRunner<Result<SearchResultValue>>
         final BitmapIndex bitmapIndex = column.getBitmapIndex();
         ExtractionFn extractionFn = dimension.getExtractionFn();
         if (extractionFn == null) {
-          extractionFn = new IdentityExtractionFn();
+          extractionFn = IdentityExtractionFn.getInstance();
         }
         if (bitmapIndex != null) {
           for (int i = 0; i < bitmapIndex.getCardinality(); ++i) {

processing/src/test/java/io/druid/query/filter/ExtractionDimFilterTest.java

@@ -35,13 +35,13 @@ public class ExtractionDimFilterTest
     ExtractionDimFilter extractionDimFilter = new ExtractionDimFilter(
         "abc",
         "d",
-        new IdentityExtractionFn(),
+        IdentityExtractionFn.getInstance(),
         null
     );
     ExtractionDimFilter extractionDimFilter2 = new ExtractionDimFilter(
         "ab",
         "cd",
-        new IdentityExtractionFn(),
+        IdentityExtractionFn.getInstance(),
         null
     );
 

processing/src/test/java/io/druid/query/groupby/having/DimensionSelectorHavingSpecTest.java

@@ -162,7 +162,7 @@ public class DimensionSelectorHavingSpecTest
   @Test
   public void testGetCacheKey()
   {
-    ExtractionFn extractionFn = new IdentityExtractionFn();
+    ExtractionFn extractionFn = IdentityExtractionFn.getInstance();
     byte[] dimBytes = "dimension".getBytes(Charsets.UTF_8);
     byte[] valBytes = "v".getBytes(Charsets.UTF_8);
     byte[] extFunKey = extractionFn.getCacheKey();