我正在用flink做一个简单的程序，但是它不会在std输出中打印任何字符串。我试过在流上使用print（）方法，在结果上使用reduce函数和after print（）方法。这是一个代码：
公共类流化作业{

public static void main(String[] args) throws Exception {
    final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
    env.enableCheckpointing(10000);
    env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);
    env.getConfig().setAutoWatermarkInterval(200L);
    List<Oggetto> objects = produciValori();
    DataStream<Oggetto> stream = env.fromCollection(objects);
    stream./*
    timeWindowAll(Time.seconds(5)).reduce(new Reduce()).*/
    print();
    env.execute("Flink Streaming Java Quickstart Mio");
}

private static List<Oggetto> produciValori() {
    List<Oggetto> objects = new ArrayList<>();
    int prop1 = 0;
    int prop2 = 1000;
    String stringa1 = "stringa1: " + prop1;
    String stringa2 = "stringa2: " + prop2;
    for (int i = 0; i < 1000; i++) {
        prop1 = prop1 + 1;
        prop2 = prop2 + 1;
        stringa1 = "stringa1: " + prop1;
        stringa2 = "stringa2: " + prop2;
        Oggetto o = new Oggetto(prop1, prop2, stringa1, stringa2);
        objects.add(o);
    }
    return objects;
}

private static class Reduce implements org.apache.flink.api.common.functions.ReduceFunction<Oggetto> {
    @Override
    public Oggetto reduce(Oggetto oggetto, Oggetto t1) throws Exception {
        if (oggetto.getPropInt1() <= t1.getPropInt1()){
            return oggetto;
        }else {
            return t1;
        }
    }
}

}