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/java/code/akka/docs/extension/ExtensionDocTestBase.java

@@ -9,63 +9,63 @@ import java.util.concurrent.atomic.AtomicLong;
 
 //#imports
 
-import org.junit.After;
-import org.junit.Before;
 import org.junit.Test;
-import static org.junit.Assert.*;
 
 public class ExtensionDocTestBase {
 
-    //#extension
-    public static class CountExtensionImpl implements Extension {
-      //Since this Extension is a shared instance
-      // per ActorSystem we need to be threadsafe
-      private final AtomicLong counter = new AtomicLong(0);
+  //#extension
+  public static class CountExtensionImpl implements Extension {
+    //Since this Extension is a shared instance
+    // per ActorSystem we need to be threadsafe
+    private final AtomicLong counter = new AtomicLong(0);
 
-      //This is the operation this Extension provides
-      public long increment()  {
-          return counter.incrementAndGet();
-      }
+    //This is the operation this Extension provides
+    public long increment() {
+      return counter.incrementAndGet();
     }
-    //#extension
+  }
 
-    //#extensionid
-    static class CountExtensionId extends AbstractExtensionId<CountExtensionImpl> {
-        //This method will be called by Akka
-        // to instantiate our Extension
-        public CountExtensionImpl createExtension(ActorSystemImpl i) {
-          return new CountExtensionImpl();
-        }
-    }
+  //#extension
 
+  //#extensionid
+  public static class CountExtension extends AbstractExtensionId<CountExtensionImpl> implements ExtensionIdProvider {
     //This will be the identifier of our CountExtension
-    public final static CountExtensionId CountExtension = new CountExtensionId();
-    //#extensionid
+    public final static CountExtension instance = new CountExtension();
 
-    //#extensionid-provider
-    static class CountExtensionIdProvider implements ExtensionIdProvider {
-        public CountExtensionId lookup() {
-          return CountExtension; //The public static final
-        }
-      }
-    //#extensionid-provider
-
-    //#extension-usage-actor
-    static class MyActor extends UntypedActor {
-      public void onReceive(Object msg) {
-        CountExtension.get(getContext().system()).increment();
-      }
+    //The lookup method is required by ExtensionIdProvider,
+    // so we return ourselves here, this allows us
+    // to configure our extension to be loaded when
+    // the ActorSystem starts up
+    public CountExtension lookup() {
+      return CountExtension.instance; //The public static final
     }
-    //#extension-usage-actor
 
+    //This method will be called by Akka
+    // to instantiate our Extension
+    public CountExtensionImpl createExtension(ActorSystemImpl system) {
+      return new CountExtensionImpl();
+    }
+  }
 
-  @Test public void demonstrateHowToCreateAndUseAnAkkaExtensionInJava() {
+  //#extensionid
+
+  //#extension-usage-actor
+  public static class MyActor extends UntypedActor {
+    public void onReceive(Object msg) {
+      CountExtension.instance.get(getContext().system()).increment();
+    }
+  }
+
+  //#extension-usage-actor
+
+  @Test
+  public void demonstrateHowToCreateAndUseAnAkkaExtensionInJava() {
     final ActorSystem system = null;
     try {
       //#extension-usage
-      CountExtension.get(system).increment();
+      CountExtension.instance.get(system).increment();
       //#extension-usage
-    } catch(Exception e) {
+    } catch (Exception e) {
       //do nothing
     }
   }

akka-docs/java/code/akka/docs/extension/SettingsExtensionDocTest.scala

@@ -0,0 +1,8 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.docs.extension
+
+import org.scalatest.junit.JUnitSuite
+
+class SettingsExtensionDocTest extends SettingsExtensionDocTestBase with JUnitSuite

akka-docs/java/code/akka/docs/extension/SettingsExtensionDocTestBase.java

@@ -0,0 +1,85 @@
+/**
+ * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.docs.extension;
+
+//#imports
+import akka.actor.Extension;
+import akka.actor.AbstractExtensionId;
+import akka.actor.ExtensionIdProvider;
+import akka.actor.ActorSystem;
+import akka.actor.ActorSystemImpl;
+import akka.util.Duration;
+import com.typesafe.config.Config;
+import java.util.concurrent.TimeUnit;
+
+//#imports
+
+import akka.actor.UntypedActor;
+import org.junit.Test;
+
+public class SettingsExtensionDocTestBase {
+
+  //#extension
+  public static class SettingsImpl implements Extension {
+
+    public final String DB_URI;
+    public final Duration CIRCUIT_BREAKER_TIMEOUT;
+
+    public SettingsImpl(Config config) {
+      DB_URI = config.getString(config.getString("myapp.db.uri"));
+      CIRCUIT_BREAKER_TIMEOUT = Duration.create(config.getMilliseconds("myapp.circuit-breaker.timeout"),
+          TimeUnit.MILLISECONDS);
+    }
+
+  }
+
+  //#extension
+
+  //#extensionid
+  public static class Settings extends AbstractExtensionId<SettingsImpl> implements ExtensionIdProvider {
+    public final static Settings instance = new Settings();
+
+    public Settings lookup() {
+      return Settings.instance;
+    }
+
+    public SettingsImpl createExtension(ActorSystemImpl system) {
+      return new SettingsImpl(system.settings().config());
+    }
+  }
+
+  //#extensionid
+
+  //#extension-usage-actor
+  public static class MyActor extends UntypedActor {
+    Connection connection = connect(Settings.instance.get(getContext().system()).DB_URI,
+        Settings.instance.get(getContext().system()).CIRCUIT_BREAKER_TIMEOUT);
+
+    //#extension-usage-actor
+
+    public Connection connect(String dbUri, Duration circuitBreakerTimeout) {
+      return new Connection();
+    }
+
+    public void onReceive(Object msg) {
+    }
+
+  }
+
+  public static class Connection {
+  }
+
+  @Test
+  public void demonstrateHowToCreateAndUseAnAkkaExtensionInJava() {
+    final ActorSystem system = null;
+    try {
+      //#extension-usage
+      String dbUri = Settings.instance.get(system).DB_URI;
+      //#extension-usage
+    } catch (Exception e) {
+      //do nothing
+    }
+  }
+
+}