FLINK-状态管理-状态使用

1.ValueState:

private var lastTempState: ValueState[Double] = _

override def open(parameters: Configuration): Unit = {
  val lastTempDescriptor = new ValueStateDescriptor[Double]("lastTemp", classOf[Double])
  lastTempState = getRuntimeContext.getState[Double](lastTempDescriptor)
}

2.ListState:

private var itemState : ListState[ItemViewCount] = _

override def open(parameters: Configuration): Unit = {
  //命名状态变量的名字和类型
  val itemStateDescription: ListStateDescriptor[ItemViewCount] = new ListStateDescriptor[ItemViewCount]("itemState", classOf[ItemViewCount])
  itemState = getRuntimeContext.getListState(itemStateDescription)
}

Flink提供了三种基于key/value的state接口，ListState接口适用于缓存多个值的计算。具体实现之前，因为state必须是基于key，且必须获取getRuntimeContext，state必须同时满足两个条件：

• 直接基于keyedStream或者由keyedStream转换来的windowedStream
• 必须继承RichFunction

实际实现时候，因为windowedStream在scala中不能实现RichWindowFunction，因此在main中使用flatmap间接实现了windowFunction中的功能：

val fromTransactionDataStream = watermarkTransaction
      .keyBy(_.code)
      .window(TumblingEventTimeWindows.of(Time.seconds(10)))
      
val transaction = fromTransactionDataStream
      .apply(new StockTransactionApply)
      .keyBy(_._3)
      .flatMap(new TransactionStateFlatMapFunction)

3.MapState

private var behaviorMapState: MapState[String, Int] = _

override def open(parameters: Configuration): Unit = {
  // 创建StateDescriptor
  val behaviorMapStateDescriptor = new MapStateDescriptor[String, Int]("behaviorMap", classOf[String], classOf[Int])
  // 通过StateDescriptor获取运行时上下文中的状态
  behaviorMapState = getRuntimeContext.getMapState(behaviorMapStateDescriptor)
}

 4.Reducing和AggregatingState

ReducingState和AggregatingState在注册StateDescriptor时，还需要实现一个ReduceFunction或AggregationFunction。下面的代码注册ReducingStateDescriptor时实现一个YourReduceFunction，YourReduceFunction实现了ReduceFunction。我们在ReducingState中使用add(in: T)方法向状态里增加一个元素，新元素和状态中已有数据通过ReduceFunction两两聚合。AggregatingState的使用方法与之类似。

val reducingStateDescriptor = new ReducingStateDescriptor[UserBehavior]("reducing", new YourReduceFunction, classOf[UserBehavior])