java - 初始化MapState的内容

Question

我已经实现了一个具有以下结构的 Flink RichFunction :

public class MyFunction extends KeyedBroadcastProcessFunction <String, InputType, BroadcastedStateType, OutputType> {

    private MapState<String, MyState> myState;              

    @Override
    public void open(Configuration conf)throws Exception{
        myState = getRuntimeContext().getMapState(new MapStateDescriptor<>("state", Types.STRING, Types.POJO(BroadcastedStateType.class)));
    }

    @Override
    public void processElement(InputType value, ReadOnlyContext ctx, Collector<OutputType> out) throws Exception {
        MyState state = myState.get(value.ID());

        // Do things
    }

    @Override
    public void processBroadcastElement(BroadcastedStateType value, Context ctx, Collector<OutputType> out) throws Exception {
        state.put(value.ID(), value.state());   // Update the mapState with value from broadcast
    }

    // retrieve all the state values and put them in the MapState
    private void initialState() throws Exception{
       Map<String, MyState> initialValues = ...;
       this.cameras.putAll(initialValues);
    }
}

mapState 变量存储通过 BroadcastedStream 更新的多个状态。更新是在 processBroadcastElement() 函数中完成的。

在作业开始时，我想使用 initialState() 函数初始化 mapState。

问题是我无法在 open() 函数中使用它(请参阅 here 为什么)

在这种情况下初始化mapState的正确方法是什么？ (并且在所有使用 RichFunctions 的情况下)

Answer 1

您想要实现 org.apache.flink.streaming.api.checkpoint.CheckpointedFunction

当您这样做时，您实现了两种方法:

@Override
public void snapshotState(FunctionSnapshotContext context) throws Exception {

    // called when it's time to save state

    myState.clear();

        // Update myState with current application state 

}

@Override
public void initializeState(FunctionInitializationContext context) throws Exception {

    // called when things start up, possibly recovering from an error

    descriptor = new MapStateDescriptor<>("state", Types.STRING, Types.POJO(BroadcastedStateType.class));

    myState = context.getKeyedStateStore().getMapState(descriptor);

    if (context.isRestored()) {

        // restore application state from myState  

    }       

}

您可以在initializeState()方法而不是open()中初始化myState变量。