document multi-arg logging, see #1856

akka-docs/java/code/akka/docs/event/LoggingDocTestBase.java

@@ -33,7 +33,7 @@ import akka.actor.DeadLetter;
 //#imports-deadletter
 
 public class LoggingDocTestBase {
-
+  
   @Test
   public void useLoggingActor() {
     ActorSystem system = ActorSystem.create("MySystem");
@@ -55,6 +55,16 @@ public class LoggingDocTestBase {
     //#deadletters
     system.shutdown();
   }
+  
+  @Test
+  public void demonstrateMultipleArgs() {
+    final ActorSystem system = ActorSystem.create("multiArg");
+    //#array
+    final Object[] args = new Object[] { "The", "brown", "fox", "jumps", 42 };
+    system.log().debug("five parameters: {}, {}, {}, {}, {}", args);
+    //#array
+    system.shutdown();
+  }
 
   //#my-actor
   class MyActor extends UntypedActor {

akka-docs/java/logging.rst

@@ -30,8 +30,13 @@ object is translated to a String according to the following rules:
   * in case of a class an approximation of its simpleName
   * and in all other cases the simpleName of its class
 
-The log message may contain argument placeholders ``{}``, which will be substituted if the log level
+The log message may contain argument placeholders ``{}``, which will be
-is enabled.
+substituted if the log level is enabled. Giving more arguments as there are
+placeholders results in a warning being appended to the log statement (i.e. on
+the same line with the same severity). You may pass a Java array as the only
+substitution argument to have its elements be treated individually:
+
+.. includecode:: code/akka/docs/event/LoggingDocTestBase.java#array
 
 The Java :class:`Class` of the log source is also included in the generated
 :class:`LogEvent`. In case of a simple string this is replaced with a “marker”

akka-docs/scala/code/akka/docs/event/LoggingDocSpec.scala

@@ -89,4 +89,11 @@ class LoggingDocSpec extends AkkaSpec {
     //#deadletters
   }
 
+  "demonstrate logging more arguments" in {
+    //#array
+    val args = Array("The", "brown", "fox", "jumps", 42)
+    system.log.debug("five parameters: {}, {}, {}, {}, {}", args)
+    //#array
+  }
+
 }

akka-docs/scala/logging.rst

@@ -34,8 +34,20 @@ The source object is translated to a String according to the following rules:
   * and in all other cases a compile error occurs unless and implicit
     :class:`LogSource[T]` is in scope for the type in question.
 
-The log message may contain argument placeholders ``{}``, which will be substituted if the log level
+The log message may contain argument placeholders ``{}``, which will be
-is enabled.
+substituted if the log level is enabled. Giving more arguments as there are
+placeholders results in a warning being appended to the log statement (i.e. on
+the same line with the same severity). You may pass a Java array as the only
+substitution argument to have its elements be treated individually:
+
+.. includecode:: code/akka/docs/event/LoggingDocSpec.scala#array
+
+The Java :class:`Class` of the log source is also included in the generated
+:class:`LogEvent`. In case of a simple string this is replaced with a “marker”
+class :class:`akka.event.DummyClassForStringSources` in order to allow special
+treatment of this case, e.g. in the SLF4J event listener which will then use
+the string instead of the class’ name for looking up the logger instance to
+use.
 
 Auxiliary logging options
 -------------------------