在要转换为 JSON 的地图定义中使用 for 循环（或迭代）

Question

我有以下代码（不起作用）定义正在转换为 JSON 的列表映射...

ObjectMapper objectMapper = new ObjectMapper();
    //Set pretty printing of json
    objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

    //Define map which will be converted to JSON
    List<TimeSeriesRollup> dataPoints = null;
    for(int i=1; i<24; i++){
    Long xVal = graphs2.get(i).get(0);
    Long yVal = graphs2.get(i).get(1);
    dataPoints = Stream.of(
            new TimeSeriesRollup(xVal, yVal))
            .collect(Collectors.toList());
    }

    List<TimeSeriesGraph> dataInfo = Stream.of(
            new TimeSeriesGraph("test", dataPoints))
            .collect(Collectors.toList());


    //1. Convert List of Person objects to JSON
    String arrayToJson = objectMapper.writeValueAsString(dataInfo);
    return arrayToJson;

所需的代码功能是这样的......

ObjectMapper objectMapper = new ObjectMapper();
    //Set pretty printing of json
    objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

    //Define map which will be converted to JSON
    List<TimeSeriesRollup> dataPoints = null;
    dataPoints = Stream.of(
            new TimeSeriesRollup(xVal1, yVal1))
            new TimeSeriesRollup(xVal2, yVal2))
            new TimeSeriesRollup(xVal3, yVal3))
            new TimeSeriesRollup(xVal, yVal))
            new TimeSeriesRollup(xVal, yVal))
            new TimeSeriesRollup(xVal, yVal)) etc...
            .collect(Collectors.toList());
    }

    List<TimeSeriesGraph> dataInfo = Stream.of(
            new TimeSeriesGraph("test", dataPoints))
            .collect(Collectors.toList());


    //1. Convert List of Person objects to JSON
    String arrayToJson = objectMapper.writeValueAsString(dataInfo);
    return arrayToJson;

我希望能够添加任意数量的“TimeSeriesRollup”，由方法中其他位置的变量定义。对此有何想法或见解？我可以提供任何其他信息吗？

Answer 1

据我了解，您需要的是从一组点组成流的索引，因此您可以从具有所需范围的Intstream 开始：

List<TimeSeriesRollup> dataPoints =
                IntStream.range(0, 24)
                         .mapToObj(graph::get)
                         .map(point -> new TimeSeriesRollup(point.get(0), point.get(1)))
                         .collect(Collectors.toList());

你可以给TimeSeriesRollup类一个静态工厂方法，输入Point，结果是：

  IntStream.range(0, 24)
           .mapToObj(graph::get)
           .map(TimeSeriesRollup::from)
           .collect(toList());