DOC: Extension sample for application specific settings. See #1702

* Added sample and documentation for how to create extension for application specific config
* Simplified java usage of ExtensionIdProvider, more aligned with how it is done in scala

akka-docs/scala/code/akka/docs/extension/ExtensionDocSpec.scala

@@ -3,16 +3,13 @@
  */
 package akka.docs.extension
 
-import org.scalatest.WordSpec
-import org.scalatest.matchers.MustMatchers
-
-//#imports
-import akka.actor._
 import java.util.concurrent.atomic.AtomicLong
-
-//#imports
+import akka.actor.Actor
+import akka.testkit.AkkaSpec
 
 //#extension
+import akka.actor.Extension
+
 class CountExtensionImpl extends Extension {
   //Since this Extension is a shared instance
   // per ActorSystem we need to be threadsafe
@@ -24,6 +21,10 @@ class CountExtensionImpl extends Extension {
 //#extension
 
 //#extensionid
+import akka.actor.ExtensionId
+import akka.actor.ExtensionIdProvider
+import akka.actor.ActorSystemImpl
+
 object CountExtension
   extends ExtensionId[CountExtensionImpl]
   with ExtensionIdProvider {
@@ -39,39 +40,37 @@ object CountExtension
 }
 //#extensionid
 
-//#extension-usage-actor
-import akka.actor.Actor
+object ExtensionDocSpec {
+  //#extension-usage-actor
 
-class MyActor extends Actor {
-  def receive = {
-    case someMessage ⇒
-      CountExtension(context.system).increment()
-  }
-}
-//#extension-usage-actor
-
-//#extension-usage-actor-trait
-import akka.actor.Actor
-
-trait Counting { self: Actor ⇒
-  def increment() = CountExtension(context.system).increment()
-}
-class MyCounterActor extends Actor with Counting {
-  def receive = {
-    case someMessage ⇒ increment()
-  }
-}
-//#extension-usage-actor-trait
-
-class ExtensionDocSpec extends WordSpec with MustMatchers {
-
-  "demonstrate how to create an extension in Scala" in {
-    val system: ActorSystem = null
-    intercept[Exception] {
-      //#extension-usage
-      CountExtension(system).increment
-      //#extension-usage
+  class MyActor extends Actor {
+    def receive = {
+      case someMessage ⇒
+        CountExtension(context.system).increment()
     }
   }
+  //#extension-usage-actor
+
+  //#extension-usage-actor-trait
+
+  trait Counting { self: Actor ⇒
+    def increment() = CountExtension(context.system).increment()
+  }
+  class MyCounterActor extends Actor with Counting {
+    def receive = {
+      case someMessage ⇒ increment()
+    }
+  }
+  //#extension-usage-actor-trait
+}
+
+class ExtensionDocSpec extends AkkaSpec {
+  import ExtensionDocSpec._
+
+  "demonstrate how to create an extension in Scala" in {
+    //#extension-usage
+    CountExtension(system).increment
+    //#extension-usage
+  }
 
 }

akka-docs/scala/code/akka/docs/extension/SettingsExtensionDocSpec.scala

@@ -0,0 +1,77 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.docs.extension
+
+//#imports
+import akka.actor.Extension
+import akka.actor.ExtensionId
+import akka.actor.ExtensionIdProvider
+import akka.actor.ActorSystemImpl
+import akka.util.Duration
+import com.typesafe.config.Config
+import java.util.concurrent.TimeUnit
+
+//#imports
+
+import akka.actor.Actor
+import akka.testkit.AkkaSpec
+
+//#extension
+class SettingsImpl(config: Config) extends Extension {
+  val DbUri: String = config.getString("myapp.db.uri")
+  val CircuitBreakerTimeout: Duration = Duration(config.getMilliseconds("myapp.circuit-breaker.timeout"), TimeUnit.MILLISECONDS)
+}
+//#extension
+
+//#extensionid
+object Settings extends ExtensionId[SettingsImpl] with ExtensionIdProvider {
+
+  override def lookup = Settings
+
+  override def createExtension(system: ActorSystemImpl) = new SettingsImpl(system.settings.config)
+}
+//#extensionid
+
+object SettingsExtensionDocSpec {
+
+  val config = """
+    //#config
+    myapp {
+      db {
+        uri = "mongodb://example1.com:27017,example2.com:27017"
+      }
+      circuit-breaker {
+        timeout = 30 seconds
+      }
+    }
+    //#config
+    """
+
+  //#extension-usage-actor
+
+  class MyActor extends Actor {
+    val connection = connect(Settings(context.system).DbUri, Settings(context.system).CircuitBreakerTimeout)
+
+    //#extension-usage-actor
+    def receive = {
+      case someMessage ⇒
+    }
+
+    def connect(dbUri: String, circuitBreakerTimeout: Duration) = {
+      "dummy"
+    }
+  }
+
+}
+
+class SettingsExtensionDocSpec extends AkkaSpec(SettingsExtensionDocSpec.config) {
+
+  "demonstrate how to create application specific settings extension in Scala" in {
+    //#extension-usage
+    val dbUri = Settings(system).DbUri
+    val circuitBreakerTimeout = Settings(system).CircuitBreakerTimeout
+    //#extension-usage
+  }
+
+}