struct streaming中的监听器StreamingQueryListener

在struct streaming提供了一个类，用来监听流的启动、停止、状态更新

StreamingQueryListener

实例化：StreamingQueryListener 后需要实现3个函数：

abstract class StreamingQueryListener {

import StreamingQueryListener._

/**
* Called when a query is started.
* @note This is called synchronously with
* [[org.apache.spark.sql.streaming.DataStreamWriter `DataStreamWriter.start()`]],
* that is, `onQueryStart` will be called on all listeners before
* `DataStreamWriter.start()` returns the corresponding [[StreamingQuery]]. Please
* don't block this method as it will block your query.
* @since 2.0.0
*/
def onQueryStarted(event: QueryStartedEvent): Unit

/**
* Called when there is some status update (ingestion rate updated, etc.)
*
* @note This method is asynchronous. The status in [[StreamingQuery]] will always be
* latest no matter when this method is called. Therefore, the status of [[StreamingQuery]]
* may be changed before/when you process the event. E.g., you may find [[StreamingQuery]]
* is terminated when you are processing `QueryProgressEvent`.
* @since 2.0.0
*/
def onQueryProgress(event: QueryProgressEvent): Unit

/**
* Called when a query is stopped, with or without error.
* @since 2.0.0
*/
def onQueryTerminated(event: QueryTerminatedEvent): Unit
}

onQueryStarted：结构化流启动的时候异步回调
onQueryProgress：查询过程中的状态发生更新时候的异步回调
onQueryTerminated：查询结束实时的异步回调

上面这些内容有什么作用？
一般在流处理中添加任务告警时候能用到。比如在onQueryStarted中判断是不是有满足告警的条件 ， 如果有的话，就发送邮件告警或者钉钉告警灯
那么在告警信息中我们就可以根据其中的exception获取报错具体详情，然后一并发送到邮件中

@InterfaceStability.Evolving
class QueryTerminatedEvent private[sql](
val id: UUID,
val runId: UUID,
val exception: Option[String]) extends Event

最后，附上一个使用的小例子：

/**
  * Created by angel
  */
object Test {
  def main(args: Array[String]): Unit = {
    val spark = SparkSession
      .builder
      .appName("IQL")
      .master("local[4]")
      .enableHiveSupport()
      .getOrCreate()
    spark.sparkContext.setLogLevel("WARN")



    // Save the code as demo-StreamingQueryManager.scala
    // Start it using spark-shell
    // $ ./bin/spark-shell -i demo-StreamingQueryManager.scala

    // Register a StreamingQueryListener to receive notifications about state changes of streaming queries
    import org.apache.spark.sql.streaming.StreamingQueryListener
    val myQueryListener = new StreamingQueryListener {
      import org.apache.spark.sql.streaming.StreamingQueryListener._
      def onQueryTerminated(event: QueryTerminatedEvent): Unit = {
        println(s"Query ${event.id} terminated")
      }

      def onQueryStarted(event: QueryStartedEvent): Unit = {
        println(s"Query ${event.id} started")
      }
      def onQueryProgress(event: QueryProgressEvent): Unit = {
        println(s"Query ${event.progress.name} process")
      }
    }
    spark.streams.addListener(myQueryListener)

    import org.apache.spark.sql.streaming._
    import scala.concurrent.duration._

    // Start streaming queries

    // Start the first query
    val q4s = spark.readStream.
      format("rate").
      load.
      writeStream.
      format("console").
      trigger(Trigger.ProcessingTime(4.seconds)).
      option("truncate", false).
      start

    // Start another query that is slightly slower
    val q10s = spark.readStream.
      format("rate").
      load.
      writeStream.
      format("console").
      trigger(Trigger.ProcessingTime(10.seconds)).
      option("truncate", false).
      start

    // Both queries run concurrently
    // You should see different outputs in the console
    // q4s prints out 4 rows every batch and twice as often as q10s
    // q10s prints out 10 rows every batch

    /*
    -------------------------------------------
    Batch: 7
    -------------------------------------------
    +-----------------------+-----+
    |timestamp              |value|
    +-----------------------+-----+
    |2017-10-27 13:44:07.462|21   |
    |2017-10-27 13:44:08.462|22   |
    |2017-10-27 13:44:09.462|23   |
    |2017-10-27 13:44:10.462|24   |
    +-----------------------+-----+

    -------------------------------------------
    Batch: 8
    -------------------------------------------
    +-----------------------+-----+
    |timestamp              |value|
    +-----------------------+-----+
    |2017-10-27 13:44:11.462|25   |
    |2017-10-27 13:44:12.462|26   |
    |2017-10-27 13:44:13.462|27   |
    |2017-10-27 13:44:14.462|28   |
    +-----------------------+-----+

    -------------------------------------------
    Batch: 2
    -------------------------------------------
    +-----------------------+-----+
    |timestamp              |value|
    +-----------------------+-----+
    |2017-10-27 13:44:09.847|6    |
    |2017-10-27 13:44:10.847|7    |
    |2017-10-27 13:44:11.847|8    |
    |2017-10-27 13:44:12.847|9    |
    |2017-10-27 13:44:13.847|10   |
    |2017-10-27 13:44:14.847|11   |
    |2017-10-27 13:44:15.847|12   |
    |2017-10-27 13:44:16.847|13   |
    |2017-10-27 13:44:17.847|14   |
    |2017-10-27 13:44:18.847|15   |
    +-----------------------+-----+
    */

    // Stop q4s on a separate thread
    // as we're about to block the current thread awaiting query termination
    import java.util.concurrent.Executors
    import java.util.concurrent.TimeUnit.SECONDS
    def queryTerminator(query: StreamingQuery) = new Runnable {
      def run = {
        println(s"Stopping streaming query: ${query.id}")
        query.stop
      }
    }
    import java.util.concurrent.TimeUnit.SECONDS
    // Stop the first query after 10 seconds
    Executors.newSingleThreadScheduledExecutor.
      scheduleWithFixedDelay(queryTerminator(q4s), 10, 60 * 5, SECONDS)
    // Stop the other query after 20 seconds
    Executors.newSingleThreadScheduledExecutor.
      scheduleWithFixedDelay(queryTerminator(q10s), 20, 60 * 5, SECONDS)

    // Use StreamingQueryManager to wait for any query termination (either q1 or q2)
    // the current thread will block indefinitely until either streaming query has finished
    spark.streams.awaitAnyTermination

    // You are here only after either streaming query has finished
    // Executing spark.streams.awaitAnyTermination again would return immediately

    // You should have received the QueryTerminatedEvent for the query termination

    // reset the last terminated streaming query
    spark.streams.resetTerminated

    // You know at least one query has terminated

    // Wait for the other query to terminate
    spark.streams.awaitAnyTermination

    assert(spark.streams.active.isEmpty)

    println("The demo went all fine. Exiting...")

    // leave spark-shell
    System.exit(0)
  }
}