refactor Jackson code to hardcode buffer-recycler

play-json/jvm/src/main/scala/play/api/libs/json/jackson/JacksonJson.scala

@@ -14,12 +14,14 @@ import scala.collection.mutable.ArrayBuffer
 import scala.collection.mutable.ListBuffer
 
 import com.fasterxml.jackson.core.JsonFactory
+import com.fasterxml.jackson.core.JsonFactoryBuilder
 import com.fasterxml.jackson.core.JsonGenerator
 import com.fasterxml.jackson.core.JsonParser
 import com.fasterxml.jackson.core.JsonTokenId
 import com.fasterxml.jackson.core.Version
 import com.fasterxml.jackson.core.json.JsonWriteFeature
 import com.fasterxml.jackson.core.util.DefaultPrettyPrinter
+import com.fasterxml.jackson.core.util.JsonRecyclerPools
 
 import com.fasterxml.jackson.databind.Module.SetupContext
 import com.fasterxml.jackson.databind._
@@ -282,9 +284,10 @@ private[json] object JacksonJson {
 }
 
 private[json] case class JacksonJson(jsonConfig: JsonConfig) {
-  private val mapper = (new ObjectMapper).registerModule(new PlayJsonMapperModule(jsonConfig))
-
-  private val jsonFactory = new JsonFactory(mapper)
+  private val jsonFactory = JsonFactory.builder()
+            .recyclerPool(JsonRecyclerPools.threadLocalPool())
+            .build()
+  private val mapper = new ObjectMapper(jsonFactory).registerModule(new PlayJsonMapperModule(jsonConfig))
 
   private def stringJsonGenerator(out: java.io.StringWriter) =
     jsonFactory.createGenerator(out)