使用 com.jackson 从 JSON 字符串中获取 Java 对象的最佳方法

Question

具体来说，我正在处理一个JSON字符串，该字符串表示包含数字和其他数字数组的数组 - 这些字符串的形式是String string = "[0, [1, 2], [3, 4]]"。 它表示形式为[ channelID, [price, amount], [price, amount] ... [price, amount]]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形式为ChannelObject { channel: 0, data: [PriceObject { price: 1, amount: 2 }, PriceObject { price: 3, amount: 4 }] }的对象。

杰克逊的本机 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给 ObjectMapper 解析器字符串{ "data": %s }，替换原始 JSON，并使用带有属性@JsonProperty ArrayNode data的类，但就性能而言，这恐怕是一种低效的方法。

为"裸"JSON 数组编写反序列化程序是最聪明的方法吗？我缺少更简单的解决方案吗？

非常感谢您的回复。

附加信息：

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

错误消息明确指定ChannelData类中没有默认构造函数(不是参数构造函数(，ChannelData类中不创建参数构造函数。

由于您声明public ChannelData(int channel, List<Data> data)ChannelData参数构造函数，因此您有责任声明任何参数构造函数

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