[SPARK-7786][STREAMING] Allow StreamingListener to be specified in SparkConf and loaded when creating StreamingContext

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -1968,7 +1968,7 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
       for (className <- listenerClassNames) {
         // Use reflection to find the right constructor
         val constructors = {
-          val listenerClass = Class.forName(className)
+          val listenerClass = org.apache.spark.util.Utils.classForName(className)
           listenerClass.getConstructors.asInstanceOf[Array[Constructor[_ <: SparkListener]]]
         }
         val constructorTakingSparkConf = constructors.find { c =>

docs/configuration.md

@@ -1493,6 +1493,17 @@ Apart from these, the following properties are also available, and may be useful
     How many batches the Spark Streaming UI and status APIs remember before garbage collecting.
   </td>
 </tr>
+<tr>
+  <td><code>spark.streaming.extraListeners</code></td>
+  <td>(none)</td>
+  <td>
+    A comma-separated list of classes that implement <code>StreamingListener</code>; when initializing
+    SparkContext, instances of these classes will be created and registered with Spark's streaming listener
+    bus.  If a class has a single-argument constructor that accepts a SparkConf, that constructor
+    will be called; otherwise, a zero-argument constructor will be called. If no valid constructor
+    can be found, the StreamingContext creation will fail with an exception.
+  </td>
+</tr>
 </table>
 
 #### SparkR

streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala

@@ -18,6 +18,7 @@
 package org.apache.spark.streaming
 
 import java.io.{InputStream, NotSerializableException}
+import java.lang.reflect.Constructor
 import java.util.concurrent.atomic.{AtomicInteger, AtomicReference}
 
 import scala.collection.Map
@@ -202,6 +203,7 @@ class StreamingContext private[streaming] (
 
   private val startSite = new AtomicReference[CallSite](null)
 
+  setupStreamingListeners()
   private var shutdownHookRef: AnyRef = _
 
   /**
@@ -538,6 +540,46 @@ class StreamingContext private[streaming] (
     scheduler.listenerBus.addListener(streamingListener)
   }
 
+  /**
+   * Registers streamingListeners specified in spark.streaming.extraListeners
+   */
+  private def setupStreamingListeners(): Unit = {
+    // Use reflection to instantiate listeners specified via `spark.streaming.extraListeners`
+    val listenerClassNames: Seq[String] =
+      conf.get("spark.streaming.extraListeners", "").split(',').map(_.trim).filter(_ != "")
+    for (className <- listenerClassNames) {
+      // Use reflection to find the right constructor
+      val constructors = {
+        val listenerClass = org.apache.spark.util.Utils.classForName(className)
+        listenerClass.getConstructors.asInstanceOf[Array[Constructor[_ <: StreamingListener]]]
+      }
+      val constructorTakingSparkConf = constructors.find { c =>
+        c.getParameterTypes.sameElements(Array(classOf[SparkConf]))
+      }
+      lazy val zeroArgumentConstructor = constructors.find { c =>
+        c.getParameterTypes.isEmpty
+      }
+      val listener: StreamingListener = {
+        if (constructorTakingSparkConf.isDefined) {
+          constructorTakingSparkConf.get.newInstance(conf)
+        } else if (zeroArgumentConstructor.isDefined) {
+          zeroArgumentConstructor.get.newInstance()
+        } else {
+          throw new SparkException(
+             s"Exception when registering Streaming Listener:" +
+              " $className did not have a zero-argument constructor or a" +
+              " single-argument constructor that accepts SparkConf. Note: if the class is" +
+              " defined inside of another Scala class, then its constructors may accept an" +
+              " implicit parameter that references the enclosing class; in this case, you must" +
+              " define the listener as a top-level class in order to prevent this extra" +
+              " parameter from breaking Spark's ability to find a valid constructor.")
+        }
+      }
+      addStreamingListener(listener)
+      logInfo(s"Registered StreamingListener $className")
+    }
+  }
+
   private def validate() {
     assert(graph != null, "Graph is null")
     graph.validate()

streaming/src/main/scala/org/apache/spark/streaming/scheduler/StreamingListener.scala

@@ -17,6 +17,8 @@
 
 package org.apache.spark.streaming.scheduler
 
+import org.apache.spark.scheduler.StatsReportListener
+
 import scala.collection.mutable.Queue
 
 import org.apache.spark.util.Distribution
@@ -81,10 +83,13 @@ trait StreamingListener {
 /**
  * :: DeveloperApi ::
  * A simple StreamingListener that logs summary statistics across Spark Streaming batches
- * @param numBatchInfos Number of last batches to consider for generating statistics (default: 10)
+ * @param numBatchInfos Number of last batches to consider for generating statistics (default: 100)
  */
 @DeveloperApi
-class StatsReportListener(numBatchInfos: Int = 10) extends StreamingListener {
+class StatsReportListener(numBatchInfos: Int) extends StreamingListener {
+
+  def this() = this(100)
+
   // Queue containing latest completed batches
   val batchInfos = new Queue[BatchInfo]()
 

streaming/src/test/scala/org/apache/spark/streaming/StreamingListenerSuite.scala

@@ -18,6 +18,7 @@
 package org.apache.spark.streaming
 
 import scala.collection.mutable.{ArrayBuffer, SynchronizedBuffer}
+import scala.collection.JavaConversions._
 import scala.concurrent.Future
 import scala.concurrent.ExecutionContext.Implicits.global
 
@@ -29,7 +30,7 @@ import org.apache.spark.streaming.scheduler._
 import org.scalatest.Matchers
 import org.scalatest.concurrent.Eventually._
 import org.scalatest.time.SpanSugar._
-import org.apache.spark.Logging
+import org.apache.spark.{SparkConf, Logging}
 
 class StreamingListenerSuite extends TestSuiteBase with Matchers {
 
@@ -140,6 +141,16 @@ class StreamingListenerSuite extends TestSuiteBase with Matchers {
     }
     true
   }
+
+  test("registering listeners via spark.streaming.extraListeners") {
+    val conf = new SparkConf().setMaster("local").setAppName("test")
+      .set("spark.streaming.extraListeners", classOf[BatchInfoCollector].getName + "," +
+        classOf[ReceiverInfoCollector].getName)
+    val scc = new StreamingContext(conf, Seconds(1))
+
+    scc.scheduler.listenerBus.listeners.exists { _.isInstanceOf[BatchInfoCollector] }
+    scc.scheduler.listenerBus.listeners.exists { _.isInstanceOf[ReceiverInfoCollector] }
+  }
 }
 
 /** Listener that collects information on processed batches */