!per #18050 Make event adapter lookup more efficient

akka-persistence-query/src/test/scala/akka/persistence/query/PersistenceQuerySpec.scala

@@ -5,12 +5,11 @@
 package akka.persistence.query
 
 import java.util.concurrent.atomic.AtomicInteger
-
 import akka.actor.ActorSystem
-import akka.persistence.journal.{ EventAdapter, EventSeq }
+import akka.persistence.journal.EventSeq
+import akka.persistence.journal.ReadEventAdapter
 import com.typesafe.config.ConfigFactory
 import org.scalatest.{ BeforeAndAfterAll, Matchers, WordSpecLike }
-
 import scala.concurrent.Await
 import scala.concurrent.duration._
 
@@ -73,9 +72,6 @@ object ExampleQueryModels {
   case class NewModel(value: String)
 }
 
-class PrefixStringWithPAdapter extends EventAdapter {
+class PrefixStringWithPAdapter extends ReadEventAdapter {
   override def fromJournal(event: Any, manifest: String) = EventSeq.single("p-" + event)
-
-  override def manifest(event: Any) = ""
-  override def toJournal(event: Any) = throw new Exception("toJournal should not be called by query side")
 }

akka-persistence/src/main/scala/akka/persistence/journal/EventAdapters.scala

@@ -16,8 +16,10 @@ import scala.collection.mutable.ArrayBuffer
 import scala.reflect.ClassTag
 import scala.util.Try
 
-/** INTERNAL API */
-private[akka] class EventAdapters(
+/**
+ * `EventAdapters` serves as a per-journal collection of bound event adapters.
+ */
+class EventAdapters(
   map: ConcurrentHashMap[Class[_], EventAdapter],
   bindings: immutable.Seq[(Class[_], EventAdapter)],
   log: LoggingAdapter) {
@@ -62,6 +64,9 @@ private[akka] object EventAdapters {
   def apply(system: ExtendedActorSystem, config: Config): EventAdapters = {
     val adapters = configToMap(config, "event-adapters")
     val adapterBindings = configToListMap(config, "event-adapter-bindings")
+    if (adapters.isEmpty && adapterBindings.isEmpty)
+      IdentityEventAdapters
+    else
       apply(system, adapters, adapterBindings)
   }
 

akka-persistence/src/main/scala/akka/persistence/journal/WriteJournalBase.scala

@@ -13,8 +13,8 @@ import akka.persistence.AtomicWrite
 private[akka] trait WriteJournalBase {
   this: Actor ⇒
 
-  lazy val persistence = Persistence(context.system)
-  private def eventAdapters = persistence.adaptersFor(self)
+  val persistence = Persistence(context.system)
+  private val eventAdapters = persistence.adaptersFor(self)
 
   protected def preparePersistentBatch(rb: immutable.Seq[PersistentEnvelope]): immutable.Seq[AtomicWrite] =
     rb.collect { // collect instead of flatMap to avoid Some allocations