使用包含变量类型字段的 Gson 反序列化 JSON 响应

Question

REST API 的响应始终返回具有以下结构的 JSON：

{
    "status": "<status_code>",
    "data": <data_object>
}

我的问题是 的值data没有唯一的类型，但它可以是字符串、JSON 对象或 JSON 数组，具体取决于调用的端点。我不知道如何以正确的方式反序列化它来创建不同的 Java 对象......

例如，我已经准备了一些POJO：根元素

public class ApiResult {

    @SerializedName("status")
    public String status;

    @SerializedName("data")
    public JsonElement data;  // should I define it as a JsonElement??
}

以及反映两个端点的两个对象：

// "data" can be a list of NavItems
public class NavItem {

    @SerializedName("id")
    public String id;

    @SerializedName("name")
    public String name;

    @SerializedName("icon")
    public String icon;

    @SuppressWarnings("serial")
    public static class List extends ArrayList<NavItem> {}
}

和

// "data" can be a single object representing a Profile
public class Profile {

    @SerializedName("id")
    public String id;

    @SerializedName("fullname")
    public String fullname;

    @SerializedName("avatar")
    public String avatar;
}

阅读了一些 StackOverflow 问题，我发现我应该使用该JsonDeserializer<T>界面。data但是如果in的类型ApiResult是可变的怎么办？

Answer 1

您应该使用自定义JsonDeserializer并在那里编写所有逻辑，如下所示

APIResult.java

public class ApiResult {

    @SerializedName("status")
    public String status;

    @SerializedName("data")
    public Object data; 
}

ApiResultDeserializer.java

import java.lang.reflect.Type;
import java.util.List;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.reflect.TypeToken;


public class ApiResultDeserializer implements JsonDeserializer<ApiResult> {

    private Type listType = new TypeToken<List<NavItem>>(){}.getType();

    @Override
    public ApiResult deserialize(JsonElement value, Type type,
            JsonDeserializationContext context) throws JsonParseException {

        final JsonObject apiResultJson = value.getAsJsonObject();

        final ApiResult result = new ApiResult();
        result.status = apiResultJson.get("status").getAsString();

        JsonElement dataJson = apiResultJson.get("data");

        if(dataJson.isJsonObject()) {
            result.data = context.deserialize(dataJson, NavItem.class);
        } else if(dataJson.isJsonPrimitive()) {
            result.data = context.deserialize(dataJson, String.class);
        } else if(dataJson.isJsonArray()) {
            result.data = context.deserialize(dataJson, listType);
        }

        return result;
    }

}

并尝试创建不同类型的data( List, Object, 或String) 正如你提到的

主程序.java

Gson gson = new GsonBuilder()
        .registerTypeAdapter(ApiResult.class, new ApiResultDeserializer())
        .create();

        List<NavItem> navItems = new ArrayList<NavItem>();

        for(int i = 1 ; i < 6 ; ++i) {
            navItems.add(new NavItem(i+"", "Name-" + i, "Icon-" + i ));
        }

        ApiResult result = new ApiResult();
        result.status = "OK";
        result.data = navItems;

        // Serialization
        System.out.println(gson.toJson(result)); // {\"status\":\"OK\",\"data\":[{\"id\":\"1\",\"name\":\"Name-1\",\"icon\":\"Icon-1\"},{\"id\":\"2\",\"name\":\"Name-2\",\"icon\":\"Icon-2\"},{\"id\":\"3\",\"name\":\"Name-3\",\"icon\":\"Icon-3\"},{\"id\":\"4\",\"name\":\"Name-4\",\"icon\":\"Icon-4\"},{\"id\":\"5\",\"name\":\"Name-5\",\"icon\":\"Icon-5\"}]}

        result.data = navItems.get(0);

        System.out.println(gson.toJson(result)); // {\"status\":\"OK\",\"data\":{\"id\":\"1\",\"name\":\"Name-1\",\"icon\":\"Icon-1\"}}

        result.data = "Test";

        System.out.println(gson.toJson(result)); // {\"status\":\"OK\",\"data\":\"Test\"}


        // Deserialization
        String input = "{\"status\":\"OK\",\"data\":[{\"id\":\"1\",\"name\":\"Name-1\",\"icon\":\"Icon-1\"},{\"id\":\"2\",\"name\":\"Name-2\",\"icon\":\"Icon-2\"},{\"id\":\"3\",\"name\":\"Name-3\",\"icon\":\"Icon-3\"},{\"id\":\"4\",\"name\":\"Name-4\",\"icon\":\"Icon-4\"},{\"id\":\"5\",\"name\":\"Name-5\",\"icon\":\"Icon-5\"}]}";

        ApiResult newResult = gson.fromJson(input, ApiResult.class);

        System.out.println(newResult.data); // Array

        input = "{\"status\":\"OK\",\"data\":{\"id\":\"1\",\"name\":\"Name-1\",\"icon\":\"Icon-1\"}}";

        newResult = gson.fromJson(input, ApiResult.class);

        System.out.println(newResult.data); // Object

        input = "{\"status\":\"OK\",\"data\":\"Test\"}";

        newResult = gson.fromJson(input, ApiResult.class);

        System.out.println(newResult.data); // String