本文将详细介绍aggregatingstate的概念、实现和使用,在需要时对数据进行聚合是现代计算机系统中的一项主要任务,这可以减少计算或存储的需求,并简化和提高系统的性能。
一、什么是aggregatingstate
aggregatingstate是Apache Flink中的一个状态类型,可以将输入的多个数据聚合为一组数据,同时也可以根据所选择的函数,更新当前的聚合结果。相比于其他状态类型,aggregatingstate提供了更为灵活的聚合方式,可以使用Flink提供的内置函数或者自定义函数去实现多种聚合方式,如平均数、最大值、最小值、加和等等。
二、aggregatingstate的实现方式
在Flink中,使用aggregatingstate需要以下步骤:
1.定义状态
定义一个Tuple类型的AggregatableTuple,包含聚合的不同类型值和一个聚合函数,示例代码如下:
public static class AggregatableTuple { int sum1; int sum2; public int getSum1() { return sum1; } public void setSum1(int sum1) { this.sum1 = sum1; } public int getSum2() { return sum2; } public void setSum2(int sum2) { this.sum2 = sum2; } public static final AggregatingStateDescriptor AGGREGATING_STATE_DESCRIPTOR = new AggregatingStateDescriptor<>("aggState", new AggregatorFunction(), TypeInformation.of(AggregatableTuple.class)); public static final class AggregatorFunction implements AggregateFunction { private static final long serialVersionUID = 1L; @Override public AggregatableTuple createAccumulator() { return new AggregatableTuple(); } @Override public AggregatableTuple add(AggregatableTuple t, AggregatableTuple acc) { acc.setSum1(t.getSum1() + acc.getSum1()); acc.setSum2(t.getSum2() + acc.getSum2()); return acc; } @Override public AggregatableTuple getResult(AggregatableTuple acc) { return acc; } @Override public AggregatableTuple merge(AggregatableTuple a, AggregatableTuple b) { a.setSum1(a.getSum1() + b.getSum1()); a.setSum2(a.getSum2() + b.getSum2()); return a; } } }
2.创建状态
使用AggregatableTuple.AGGREGATING_STATE_DESCRIPTOR创建aggregatingstate类型状态,示例代码如下:
private static final AggregatingStateDescriptor AGGREGATING_STATE_DESCRIPTOR = AggregatableTuple.AGGREGATING_STATE_DESCRIPTOR; private AggregatingStateaggregatingState; @Override public void open(Configuration parameters) throws Exception { super.open(parameters); aggregatingState = getRuntimeContext().getAggregatingState(AGGREGATING_STATE_DESCRIPTOR); }
3.使用状态
使用aggregatingstate的add方法来将输入数据合并到当前的聚合结果中,最后使用get方法获取聚合结果,示例代码如下:
@Override public void processElement(Integer value, Context context, Collectorcollector) throws Exception { aggregatingState.add(value); AggregatableTuple result = aggregatingState.get(); collector.collect(result.getSum1()); }
三、如何使用aggregatingstate
下面将说明使用aggregatingstate实现平均值的方式:
1.定义状态
定义AggregatableTuple类型的变量作为状态,包含两个int型变量(sum和count)和一个聚合函数,示例代码如下:
public static class AggregatableTuple { int sum; int count; public int getSum() { return sum; } public void setSum(int sum) { this.sum = sum; } public int getCount() { return count; } public void setCount(int count) { this.count = count; } public static final AggregatingStateDescriptor AGGREGATING_STATE_DESCRIPTOR = new AggregatingStateDescriptor<>("aggState", new AggregatorFunction(), TypeInformation.of(AggregatableTuple.class)); public static final class AggregatorFunction implements AggregateFunction{ private static final long serialVersionUID = 1L; @Override public AggregatableTuple createAccumulator() { return new AggregatableTuple(); } @Override public AggregatableTuple add(Integer value, AggregatableTuple accumulator) { accumulator.setSum(accumulator.getSum() + value); accumulator.setCount(accumulator.getCount() + 1); return accumulator; } @Override public AggregatableTuple getResult(AggregatableTuple accumulator) { return accumulator; } @Override public AggregatableTuple merge(AggregatableTuple a, AggregatableTuple b) { a.setSum(a.getSum() + b.getSum()); a.setCount(a.getCount() + b.getCount()); return a; } } }
2.创建状态
在Task中使用getAggregatingState方法创建aggregatingstate类型状态,示例代码如下:
private AggregatingStatesumState; @Override public void open(Configuration parameters) throws Exception { super.open(parameters); sumState = getRuntimeContext().getAggregatingState(AggregatableTuple.AGGREGATING_STATE_DESCRIPTOR); }
3.实现平均值
在processElement方法中添加数据并更新聚合结果,最后使用get方法获取聚合结果,然后计算平均值并返回,示例代码如下:
@Override public void processElement(Integer value, Context ctx, Collector> out) throws Exception { sumState.add(value); AggregatableTuple res = sumState.get(); if (res.getCount() != 0) { double avg = (double) res.getSum() / res.getCount(); out.collect(new Tuple2<>(ctx.timerService().currentProcessingTime(), avg)); } }
四、总结
aggregatingstate可以将输入数据聚合成一组数据,同时可以使用Flink提供的内置函数或者自定义函数去实现多种聚合方式。通过本文的介绍,你已经掌握了aggregatingstate的概念、实现和使用方法,可以更加灵活地使用Flink实现各种不同的聚合操作。