如何在flink流处理中对带过滤器的键控流添加处理函数？

import org.apache.flink.api.common.functions.FilterFunction;
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 FlinkStreamProcessingExample {

    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        // 创建一个带过滤器的键控流
        DataStream<Tuple2<String, Integer>> keyedStream = env.fromElements(
                new Tuple2<>("key1", 10),
                new Tuple2<>("key2", 20),
                new Tuple2<>("key1", 30),
                new Tuple2<>("key2", 40))
                .keyBy(0)
                .filter(new FilterFunction<Tuple2<String, Integer>>() {
                    @Override
                    public boolean filter(Tuple2<String, Integer> value) throws Exception {
                        // 过滤出键为 "key1" 的数据
                        return value.f0.equals("key1");
                    }
                });

        // 对过滤后的键控流添加处理函数
        keyedStream.process(new CustomProcessFunction())
                .print();

        env.execute("Flink Stream Processing Example");
    }

    // 自定义处理函数
    public static class CustomProcessFunction extends ProcessFunction<Tuple2<String, Integer>, String> {
        @Override
        public void processElement(Tuple2<String, Integer> value, Context ctx, Collector<String> out) throws Exception {
            // 对每个元素进行处理，这里仅将数据转换成字符串并输出
            out.collect(value.toString());
        }
    }
}