java - 使用 jackson 反序列化包含 @JsonFormat(shape=JsonFormat.Shape.ARRAY) 和自定义对象的 json

Question

我有一个自定义对象:

public class Response
{
    @JsonProperty("values")
    private List<Value> values;

    @JsonFormat(shape=JsonFormat.Shape.ARRAY)
    public static class Value {

        public Value(long timestamp, float val)
        {
            this.timestamp = timestamp;
            this.val = val;
        }
    }
}

但是当解析它时，我得到“无法从 START_ARRAY token 中反序列化 Response$Value 的实例”。json 是:

{
"values":[[1552215648,18]]
}

知道我是否在这里遗漏了什么吗？或者我应该有一个自定义解串器来执行此操作？

Answer 1

JsonFormat 可以解决问题，但您还需要使用 JsonCreator 注释声明构造函数。看看下面的例子:

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.util.List;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        Response myPojo = mapper.readValue(jsonFile, Response.class);
        System.out.println(myPojo);
    }
}

class Response {

    private List<Value> values;

    public List<Value> getValues() {
        return values;
    }

    public void setValues(List<Value> values) {
        this.values = values;
    }

    @Override
    public String toString() {
        return "Response{" +
                "values=" + values +
                '}';
    }
}

@JsonFormat(shape = JsonFormat.Shape.ARRAY)
class Value {

    private long timestamp;
    private float val;

    @JsonCreator
    public Value(@JsonProperty("timestamp") long timestamp, @JsonProperty("val") float val) {
        this.timestamp = timestamp;
        this.val = val;
    }

    public long getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(long timestamp) {
        this.timestamp = timestamp;
    }

    public float getVal() {
        return val;
    }

    public void setVal(float val) {
        this.val = val;
    }

    @Override
    public String toString() {
        return "Value{" +
                "timestamp=" + timestamp +
                ", val=" + val +
                '}';
    }
}

以上代码用于以下 JSON 有效负载:

{
  "values": [
    [
      1552215648,
      18
    ],
    [
      123,
      12.24
    ]
  ]
}

打印:

Response{values=[Value{timestamp=1552215648, val=18.0}, Value{timestamp=123, val=12.24}]}