updateStateByKey
是Flink早期版本中提供的方法,它允许你根据键来更新状态,这个方法接受一个初始状态,一个状态更新函数和一个键值对输入流,当输入流中的键与当前状态中的键匹配时,状态更新函数会被调用,并使用新的值来更新状态,如果输入流中的键与当前状态中的键不匹配,那么状态将保持不变。
下面是一个使用updateStateByKey
的示例代码:
import org.apache.flink.api.common.functions.UpdateStateKeyFunction; import org.apache.flink.api.common.state.MapState; import org.apache.flink.api.common.state.MapStateDescriptor; import org.apache.flink.api.java.tuple.Tuple2; import org.apache.flink.streaming.api.datastream.DataStream; import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment; public class UpdateStateByKeyExample { public static void main(String[] args) throws Exception { StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment(); DataStream<Tuple2<String, Integer>> dataStream = env.fromElements( new Tuple2<>("key1", 1), new Tuple2<>("key1", 2), new Tuple2<>("key2", 3) ); MapStateDescriptor<String, Integer> stateDescriptor = new MapStateDescriptor<>( "state", String.class, Integer.class ); DataStream<Tuple2<String, Integer>> result = dataStream .updateStateByKey(new UpdateStateKeyFunction<Tuple2<String, Integer>>() { private MapState<String, Integer> state; @Override public void open(Configuration parameters) throws Exception { state = getRuntimeContext().getMapState(stateDescriptor); } @Override public void updateKeyedState(Tuple2<String, Integer> value) throws Exception { state.put(value.f0, value.f1); } }); result.print(); env.execute(); } }
在上面的示例中,我们创建了一个包含键值对的DataStream,并使用updateStateByKey
方法来根据键更新状态,我们定义了一个UpdateStateKeyFunction
,并在open
方法中获取了MapState的引用,在updateKeyedState
方法中,我们将输入流中的值添加到MapState中,我们打印出处理后的结果。
随着Flink的发展,updateStateByKey
方法被视为过时的,并在后续版本中被弃用,取而代之的是mapWithState
方法,与updateStateByKey
相比,mapWithState
提供了更灵活的状态管理功能,并支持更复杂的逻辑,它允许你在每个事件上执行自定义的映射操作,并根据需要更新状态。mapWithState
还提供了更多的状态操作,如删除状态和清除状态。
下面是一个使用mapWithState
的示例代码:
import org.apache.flink.api.common.state.MapStateDescriptor; import org.apache.flink.api.java.tuple.Tuple2; import org.apache.flink.streaming.api.datastream.DataStream; import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment; import org.apache.flink.streaming.api.functions.ProcessFunction; import org.apache.flink.util.Collector; public class MapWithStateExample { public static void main(String[] args) throws Exception { StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment(); DataStream<Tuple2<String, Integer>> dataStream = env.fromElements( new Tuple2<>("key1", 1), new Tuple2<>("key1", 2), new Tuple2<>("key2", 3) ); MapStateDescriptor<String, Integer> stateDescriptor = new MapStateDescriptor<>( "state", String.class, Integer.class ); DataStream<Tuple2<String, Integer>> result = dataStream .process(new ProcessFunction<
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