java - 使用 com.jackson 从 JSON 字符串获取 Java 对象的最佳方法？

Question

具体来说，我正在处理一个 JSON 字符串，表示一个包含数字和其他数字数组的数组 - 这些字符串的形式为 String string = "[0, [1, 2], [3, 4] ]”。它表示 [channelID, [price, amount], [price, amount] ... [price, amount]] 形式的数据；重复数据的长度可以不同。

我的最终目标是将此字符串转换为 ChannelObject {channel: 0, data: [PriceObject {price: 1, amount: 2 }, PriceObject {price: 3, amount: 4 } 形式的对象] }。

Jackson 的 native objectMapper 在尝试将未封装的 JSON 数组的值读取到类时抛出错误，我找到的唯一解决方案是为 ObjectMapper 解析器提供字符串 { "data": %s }，替换原来的 JSON，并使用带有属性 @JsonProperty ArrayNode data 的类，但就性能而言，恐怕这是一种低效的方法。

为“裸”JSON 数组编写反序列化器是最明智的方法吗？我缺少更简单的解决方案吗？

非常感谢您的回复。

其他信息:

ObjectMapper 不起作用。

public static void main(String args[]) {
    String input = "[17847,[5391.9,0,-1]";
    ObjectMapper mapper = new ObjectMapper();
    List<ChannelData> list = mapper.readValue(input, ChannelData[].class);
}

public class ChannelData {
    private int channel;

    private List<Data> data;

    public ChannelData(int channel, List<Data> data) {
        this.channel = channel;
        this.data = data;
    }

    public int getChannel() {
        return channel;
    }

    public void setChannel(int channel) {
        this.channel = channel;
    }

    public List<Data> getData() {
        return data;
    }

    public void setData(List<Data> data) {
        this.data = data;
    }
}

public class Data {
    private BigDecimal price;

    private int count;

    private BigDecimal amount;

    public Data() {
    }

    public Data(BigDecimal price, int count, BigDecimal amount) {
        this.price = price;
        this.count = count;
        this.amount = amount;
    }

    public BigDecimal getPrice() {
        return price;
    }

    public void setPrice(BigDecimal price) {
        this.price = price;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

    public BigDecimal getAmount() {
        return amount;
    }

    public void setAmount(BigDecimal amount) {
        this.amount = amount;
    }
}

错误:

Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `co.myproject.Application$ChannelData` (no Creators, like default construct, exist): no int/Int-argument constructor/factory method to deserialize from Number value (17847)
 at [Source: (String)"[17847,[5391.9,0,-1]]"; line: 1, column: 2] (through reference chain: java.lang.Object[][0])
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1451)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1027)
    at com.fasterxml.jackson.databind.deser.ValueInstantiator.createFromInt(ValueInstantiator.java:262)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromInt(StdValueInstantiator.java:356)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromNumber(BeanDeserializerBase.java:1324)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:173)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:161)
    at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:195)
    at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:21)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3004)
    at co.myproject.Application.run(Application.java:27)
    at co.myproject.Application.main(Application.java:39)

Process finished with exit code 1

Answer 1

错误消息明确指出您的 ChannelData 中没有默认构造函数(即无参数构造函数)。类，在 ChannelData 中创建无参数构造函数类。

自从您声明 public ChannelData(int channel, List<Data> data) ChannelData有参构造函数，您有责任声明无参构造函数

public class ChannelData {
      public ChannelData() { // no arg constructor }