GSON can be an array of string or an array of object

问题

I'm trying to create a GSON class but not sure how to handle this case.

According to the API specifications options can be a list values: ["one", "two"] OR

can be a list of {"value": "Label"} pairs to provide labels for values

{
...
  "options": ["one", "two", "three"],
}

{
...
  "options": [{"light": "Solarized light"}, {"dark": "Solarized dark"}],
}

回答1:

You can map this field to Map<String, String>:

class Pojo {

    @JsonAdapter(OptionsJsonDeserializer.class)
    private Map<String, String> options;

    // getters, setters, toString, other properties
}

List of primitives means that you have only values (without labels). In case of list of JSON Objects you have values with labels. Now, you need to implement custom deserialiser for given property:

class OptionsJsonDeserializer implements JsonDeserializer<Map<String, String>> {

    @Override
    public Map<String, String> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        if (json.isJsonArray()) {
            Map<String, String> map = new HashMap<>();
            JsonArray array = json.getAsJsonArray();
            array.forEach(item -> {
                if (item.isJsonPrimitive()) {
                    map.put(item.getAsString(), null);
                } else if (item.isJsonObject()) {
                    item.getAsJsonObject().entrySet().forEach(entry -> {
                        map.put(entry.getKey(), entry.getValue().getAsString());
                    });
                }
            });

            return map;
        }

        return Collections.emptyMap();
    }
}

Simple usage:

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonArray;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.annotations.JsonAdapter;

import java.io.File;
import java.io.FileReader;
import java.lang.reflect.Type;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

public class GsonApp {

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

        Gson gson = new GsonBuilder().create();

        Pojo pojo = gson.fromJson(new FileReader(jsonFile), Pojo.class);
        System.out.println(pojo);
    }
}

For JSON objects:

{
  "options": [
    {
      "light": "Solarized light"
    },
    {
      "dark": "Solarized dark"
    }
  ]
}

prints:

Pojo{options={light=Solarized light, dark=Solarized dark}}

For list of primitives:

{
  "options": [
    "one",
    "two",
    "three"
  ]
}

Prints:

Pojo{options={one=null, two=null, three=null}}

来源：https://stackoverflow.com/questions/56011652/gson-can-be-an-array-of-string-or-an-array-of-object

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java

gson