如何将异构 JSON 数组映射到 Java 对象？

Question

我通过 API 下载了大量的历史加密市场数据。它的格式如下：

[
[1601510400000,"4.15540000","4.16450000","4.15010000","4.15030000","4483.01000000",1601510459999,"18646.50051400",50,"2943.27000000","12241.83706500","0"],
...
[1609490340000,"4.94020000","4.95970000","4.93880000","4.94950000","5307.62000000",1609490399999,"26280.03711000",98,"3751.46000000","18574.22402400","0"]
]

我认为它是一个数组数组，内部数组包含异构类型（始终以相同的顺序排列相同的类型）。作为中间步骤，我已将其保存到文本文件中，但我想将其读回并将其映射到此类对象的数组中：

    public class MinuteCandle {
        private long openTime;
        private double openValue;
        private double highValue;
        private double lowValue;
        private double closeValue;
        private double volume;
        private long closeTime;
        private double quoteAssetVolume;
        private int numberOfTrades;
        private double takerBuyBaseAssetVolume;
        private double takerBuyQuoteAssetVolume;
        private double someGarbageData;
//...
}

我正在使用 Spring Framework 和 jackson 库进行 json 映射。这样做可行还是我应该以某种方式手动解析文本？

Answer 1

使用JsonFormat 并在您将形状指定为ARRAY 的地方用它注释您的类：

@JsonFormat(shape = JsonFormat.Shape.ARRAY)
class MinuteCandle

另外，如果您想存储价格，请考虑使用BigDecimal 而不是double。

另见：

• A realistic example where using BigDecimal for currency is strictly better than using double
• How to deserialise anonymous array of mixed types with Jackson

Answer 2

我会分两步完成：

1. 使用 Jackson 将 JSON 内容读入List<Object> 列表。
2. 将每个List<Object> 转换为MinuteCandle 对象 并将这些对象收集到MinuteCandles 列表中。

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {

    public static void main(String[] args) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();
        File file = new File("example.json");
        List<List<Object>> lists = objectMapper.readValue(file, new TypeReference<List<List<Object>>>() {});
        List<MinuteCandle> minuteCandles = new ArrayList<>();
        for (List<Object> list : lists) {
            minuteCandles.add(MinuteCandle.createFromList(list));
        }
    }
}

从List<Object> 到MinuteCandle 的转换（上面的第2 步） 可以通过在 MinuteCandle 类中添加静态方法来实现。

public static MinuteCandle createFromList(List<Object> list) {
    MinuteCandle m = new MinuteCandle();
    m.openTime = (Long) list.get(0);
    m.openValue = Double.parseDouble((String) list.get(1));
    m.highValue = Double.parseDouble((String) list.get(2));
    m.lowValue = Double.parseDouble((String) list.get(3));
    m.closeValue = Double.parseDouble((String) list.get(4));
    m.volume = Double.parseDouble((String) list.get(5));
    m.closeTime = (Long) list.get(6);
    m.quoteAssetVolume = Double.parseDouble((String) list.get(7));
    m.numberOfTrades = (Integer) list.get(8);
    m.takerBuyBaseAssetVolume = Double.parseDouble((String) list.get(9));
    m.takerBuyQuoteAssetVolume = Double.parseDouble((String) list.get(10));
    m.someGarbageData = Double.parseDouble((String) list.get(11));
    return m;
}

Answer 3

假设文件中存储的文本是有效的JSON，类似How to Read JSON data from txt file in Java?中的解决方案可以使用com.google.gson.Gson如下：

import com.google.gson.Gson;
import java.io.FileReader;
import java.io.Reader;

public class Main {
    public static void main(String[] args) throws Exception {
        try (Reader reader = new FileReader("somefile.txt")) {
            Gson gson = new Gson();
            MinuteCandle[] features = gson.fromJson(reader, MinuteCandle[].class);
        }
    }
}