如何使用杰克逊反序列化混合类型的匿名数组 [英] How to deserialise anonymous array of mixed types with Jackson

问题描述

在我的Java程序中，我试图解析从 Strava.com 的API获取的数据.我从那里收到的JSON有效载荷之一如下:

[
  {"type": "altitude","data": [519.1,519.3,519.3,519.4,519.5],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "latlng","data": [[46.01234,6.01234],[46.11234,6.11234],[46.21234,6.21234],[46.31234,6.31234],[46.41234,6.41234]],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "velocity_smooth","data": [0.0,0.0,0.0,5.5,5.2],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "distance","data": [0.0,8.6,11.8,16.6,20.8],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "time","data": [0,1,2,3,4],"series_type": "distance","original_size": 5,"resolution": "high"}
]

基本上，这些条目中的四个(海拔高度，speed_smooth，距离和时间)具有相同的结构(它们的data字段是双精度数组(或可以解析为双精度整数的整数))，但是第二个条目( latlng)对data字段具有不同的结构(它是一个由double组成的数组的数组).

如果所有内容都被命名，我对Jackson库很熟悉，可以在JSON和POJO之间进行转换，但是看不到如何对上述数据结构进行反序列化.

让我们说，它看起来不是上面的数据，而是:

{
  "altitude": {"data": [519.1,519.3,519.3,519.4,519.5],"series_type": "distance","original_size": 5,"resolution": "high"},
  "latlng":  {"data": [[46.01234,6.01234],[46.11234,6.11234],[46.21234,6.21234],[46.31234,6.31234],[46.41234,6.41234]],"series_type": "distance","original_size": 5,"resolution": "high"},
  "velocity_smooth": {"data": [0.0,0.0,0.0,5.5,5.2],"series_type": "distance","original_size": 5,"resolution": "high"},
  "distance":  {"data": [0.0,8.6,11.8,16.6,20.8],"series_type": "distance","original_size": 5,"resolution": "high"},
  "time": {"data": [0,1,2,3,4],"series_type": "distance","original_size": 5,"resolution": "high"}
}

然后我可以定义以下三个类

import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.AllArgsConstructor;
import lombok.Value;
import java.util.List;

@Getter
@NoArgsConstructor
public class Holder {
  DoubleData altitude;
  CoordinateData latlng;
  @JsonProperty("velocity_smooth") DoubleData velocitySmooth;
  DoubleData distance;
  DoubleData time;
}

@Getter
@NoArgsConstructor
public class DoubleData {
  List<Double> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

@Getter
@NoArgsConstructor
public class CoordinateData {
  List<List<Double>> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

然后使用

objectMapper.readValue(jsonString, Holder.class);

以读取该对象.但是，由于从Strava接收的数据是数组而不是对象，所以我失败了.我已阅读 Baeldung关于如何解组集合/数组的文章，但前提是所有这些数组/集合中的类相同.

我虽然要定义一个接口，该接口将由数组中可以找到的两个类扩展，然后使用该机制:

public interface Data {
}

@Getter
@NoArgsConstructor
public class DoubleData implements Data {
  String type;
  List<Double> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

@Getter
@NoArgsConstructor
public class CoordinateData implements Data {
  String type;
  List<List<Double>> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

Data[] array = objectMapper.readValue(jsonString, Data[].class);

但是那是行不通的，因为我需要找到某种方式让它找出何时使用DoubleData类以及何时使用CoordinateData类.

我确定，我不是尝试使用Java中Strava数据的第一个人.能做到吗?

解决方案

如果可能的话，您绝对应该使用他们的客户端. Strava API v3 显示了许多示例如何将API及其模型一起使用. /p>

如果要实现自己的模型，则应考虑继承和com.fasterxml.jackson.annotation.JsonTypeInfo，com.fasterxml.jackson.annotation.JsonSubTypes批注.同样，类型为latlng的JSON Object包含以array形式在JSON中表示的对象列表.我们可以使用com.fasterxml.jackson.annotation.JsonFormat注释来处理.一起给出:

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

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

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

        ObjectMapper mapper = new ObjectMapper();
        mapper.readValue(jsonFile, new TypeReference<List<Data>>() {}).forEach(System.out::println);
    }
}

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.EXISTING_PROPERTY,
        visible = true,
        property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(name = "altitude", value = DoubleData.class),
        @JsonSubTypes.Type(name = "latlng", value = CoordinateData.class),
        @JsonSubTypes.Type(name = "velocity_smooth", value = DoubleData.class),
        @JsonSubTypes.Type(name = "distance", value = DoubleData.class),
        @JsonSubTypes.Type(name = "time", value = DoubleData.class)
})
abstract class Data<T> {

    private String type;

    @JsonProperty("series_type")
    private String seriesType;

    @JsonProperty("original_size")
    private Integer originalSize;

    private String resolution;

    private List<T> data;

    // getters, setters, toString
}


class DoubleData extends Data<Double> {

}

class CoordinateData extends Data<Coordinates> {

}

@JsonFormat(shape = JsonFormat.Shape.ARRAY)
class Coordinates {
    private double lat;
    private double lng;

        // getters, setters, toString
}

上面的代码显示:

Data[type='altitude', seriesType='distance', originalSize=5, resolution='high', data=[519.1, 519.3, 519.3, 519.4, 519.5]]
Data[type='latlng', seriesType='distance', originalSize=5, resolution='high', data=[Coordinates[lat=46.01234, lng=6.01234], Coordinates[lat=46.11234, lng=6.11234], Coordinates[lat=46.21234, lng=6.21234], Coordinates[lat=46.31234, lng=6.31234], Coordinates[lat=46.41234, lng=6.41234]]]
Data[type='velocity_smooth', seriesType='distance', originalSize=5, resolution='high', data=[0.0, 0.0, 0.0, 5.5, 5.2]]
Data[type='distance', seriesType='distance', originalSize=5, resolution='high', data=[0.0, 8.6, 11.8, 16.6, 20.8]]
Data[type='time', seriesType='distance', originalSize=5, resolution='high', data=[0.0, 1.0, 2.0, 3.0, 4.0]]

您还应该查看 Google开发人员小组和请咨询此解决方案.

In my Java program, I am trying to parse data that I get from Strava.com's API. One of the JSON payloads, I receive from there looks as follows:

[
  {"type": "altitude","data": [519.1,519.3,519.3,519.4,519.5],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "latlng","data": [[46.01234,6.01234],[46.11234,6.11234],[46.21234,6.21234],[46.31234,6.31234],[46.41234,6.41234]],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "velocity_smooth","data": [0.0,0.0,0.0,5.5,5.2],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "distance","data": [0.0,8.6,11.8,16.6,20.8],"series_type": "distance","original_size": 5,"resolution": "high"},
  {"type": "time","data": [0,1,2,3,4],"series_type": "distance","original_size": 5,"resolution": "high"}
]

Basically, four of these entries (altitude, velocity_smooth, distance and time) have the same structure (their data field is an array of doubles (or ints that can be parsed as doubles)), but the second entry (latlng) has a slighlty different structure for the data field (it is a an array of arrays of double).

I am familiar with the Jackson library to convert between JSON and POJOs if all the content is named, but do not see how I can model the above data structure to deserialise it.

Let's say that instead of the data above, it looked as follows:

{
  "altitude": {"data": [519.1,519.3,519.3,519.4,519.5],"series_type": "distance","original_size": 5,"resolution": "high"},
  "latlng":  {"data": [[46.01234,6.01234],[46.11234,6.11234],[46.21234,6.21234],[46.31234,6.31234],[46.41234,6.41234]],"series_type": "distance","original_size": 5,"resolution": "high"},
  "velocity_smooth": {"data": [0.0,0.0,0.0,5.5,5.2],"series_type": "distance","original_size": 5,"resolution": "high"},
  "distance":  {"data": [0.0,8.6,11.8,16.6,20.8],"series_type": "distance","original_size": 5,"resolution": "high"},
  "time": {"data": [0,1,2,3,4],"series_type": "distance","original_size": 5,"resolution": "high"}
}

Then I could define the following three classes

import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.AllArgsConstructor;
import lombok.Value;
import java.util.List;

@Getter
@NoArgsConstructor
public class Holder {
  DoubleData altitude;
  CoordinateData latlng;
  @JsonProperty("velocity_smooth") DoubleData velocitySmooth;
  DoubleData distance;
  DoubleData time;
}

@Getter
@NoArgsConstructor
public class DoubleData {
  List<Double> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

@Getter
@NoArgsConstructor
public class CoordinateData {
  List<List<Double>> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

And then use

objectMapper.readValue(jsonString, Holder.class);

to read in that object. However, as the data received from Strava is an array instead of an object, I am failing. I have read Baeldung's article on how to unmarshal to collections/arrays but that assumes that all classes in the array/collection are the same.

I though about defining an interface which would be extended by the two classes that could be found in the array and then use that mechanism:

public interface Data {
}

@Getter
@NoArgsConstructor
public class DoubleData implements Data {
  String type;
  List<Double> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

@Getter
@NoArgsConstructor
public class CoordinateData implements Data {
  String type;
  List<List<Double>> data;
  @JsonProperty("series_type")   String seriesType;
  @JsonProperty("original_size") Integer originalSize;
  String resolution;
}

Data[] array = objectMapper.readValue(jsonString, Data[].class);

But that doesn't work, as I would need to find some way to let it find out when to use a DoubleData class and when to use a CoordinateData class.

I am sure, I am not the first person trying to use Strava data in Java. Can this be done?

解决方案

If possible, you should definitely use their's client. Strava API v3 shows many examples how to use this API together with theirs model.

If you want to implement your own model you should consider inheritance and com.fasterxml.jackson.annotation.JsonTypeInfo, com.fasterxml.jackson.annotation.JsonSubTypes annotations. Also, JSON Object with type latlng contains list of objects which are represented in JSON in form of array. We can handle this using com.fasterxml.jackson.annotation.JsonFormat annotation. All together gives:

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

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

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

        ObjectMapper mapper = new ObjectMapper();
        mapper.readValue(jsonFile, new TypeReference<List<Data>>() {}).forEach(System.out::println);
    }
}

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.EXISTING_PROPERTY,
        visible = true,
        property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(name = "altitude", value = DoubleData.class),
        @JsonSubTypes.Type(name = "latlng", value = CoordinateData.class),
        @JsonSubTypes.Type(name = "velocity_smooth", value = DoubleData.class),
        @JsonSubTypes.Type(name = "distance", value = DoubleData.class),
        @JsonSubTypes.Type(name = "time", value = DoubleData.class)
})
abstract class Data<T> {

    private String type;

    @JsonProperty("series_type")
    private String seriesType;

    @JsonProperty("original_size")
    private Integer originalSize;

    private String resolution;

    private List<T> data;

    // getters, setters, toString
}


class DoubleData extends Data<Double> {

}

class CoordinateData extends Data<Coordinates> {

}

@JsonFormat(shape = JsonFormat.Shape.ARRAY)
class Coordinates {
    private double lat;
    private double lng;

        // getters, setters, toString
}

Above code prints:

Data[type='altitude', seriesType='distance', originalSize=5, resolution='high', data=[519.1, 519.3, 519.3, 519.4, 519.5]]
Data[type='latlng', seriesType='distance', originalSize=5, resolution='high', data=[Coordinates[lat=46.01234, lng=6.01234], Coordinates[lat=46.11234, lng=6.11234], Coordinates[lat=46.21234, lng=6.21234], Coordinates[lat=46.31234, lng=6.31234], Coordinates[lat=46.41234, lng=6.41234]]]
Data[type='velocity_smooth', seriesType='distance', originalSize=5, resolution='high', data=[0.0, 0.0, 0.0, 5.5, 5.2]]
Data[type='distance', seriesType='distance', originalSize=5, resolution='high', data=[0.0, 8.6, 11.8, 16.6, 20.8]]
Data[type='time', seriesType='distance', originalSize=5, resolution='high', data=[0.0, 1.0, 2.0, 3.0, 4.0]]

You should also take a look on Google Dev Group and consult this solution.

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