java - 将 JSON 转换为排序 JSON，其中包含嵌套节点中的 JSONArray

Question

这里我想知道，如何将未排序的 JSON 字符串转换为包含多个 JSON 的已排序 JSON 字符串数组作为子元素。下面给出了未排序的 JSON 字符串示例，

{
    "name": "John",
    "age": 22,
    "foods": [{
            "product": "apple",
            "price": 100
        }, {
            "fruit": "banana",
            "price": 100
        }
    ],

    "attributes": {
        "OBJECTID": "35",
        "FACILITYTYPE": "Pharmacy",
        "FACILITYSUBTYPE": "24 Hr Pharmacy",
        "COMMERCIALNAME_E": "SADD MAARAB PHARMACY"
    }
}

预期输出如下，

{
    "age": 22,
    "attributes": {
        "COMMERCIALNAME_E": "SADD MAARAB PHARMACY",
        "FACILITYSUBTYPE": "24 Hr Pharmacy",
        "FACILITYTYPE": "Pharmacy",
        "OBJECTID": "35"
    },
    "foods": [{
            "price": 100m
            "product": "apple"
        }, {
            "fruit": "banana",
            "price": 100
        }
    ],
    "name": "John",
}

有人可以帮助我实现这个要求吗？

Answer 1

JSON Object在Java可以表示为Map<String, Object>和JSON Array可以表示为List , Set , array[]或任何其他 Collection 。最流行的库如Jackson和 Gson默认情况下可以这样做。对于 JSON Object documentation说:

An object is an unordered set of name/value pairs.

因此，大多数库默认情况下不关心顺序并使用无序 Map实现。最多可以维持 JSON 的订单使用LinkedHashMap有效负载或任何其他类似的实现。但为了强制排序，我们需要自定义配置。

对于Gson它可以看起来像这样:

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.Map;
import java.util.TreeMap;

public class GsonApp {

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

        Gson gson = new GsonBuilder()
                .setPrettyPrinting()
                .registerTypeAdapterFactory(new TreeMapTypeAdapterFactory())
                .create();

        Map root = gson.fromJson(new FileReader(jsonFile), Map.class);
        System.out.println(gson.toJson(root));
    }
}

class TreeMapTypeAdapterFactory implements TypeAdapterFactory {

    public final <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        if (Map.class.isAssignableFrom(type.getRawType())) {
            final TypeAdapter<T> delegate = gson.getDelegateAdapter(this, type);
            return createCustomTypeAdapter(delegate);
        }

        return null;
    }

    private <T> TypeAdapter<T> createCustomTypeAdapter(TypeAdapter<T> delegate) {
        return new TypeAdapter<T>() {
            @Override
            public void write(JsonWriter out, T value) throws IOException {
                Map map = (Map) value;
                delegate.write(out, (T) new TreeMap(map));
            }

            @Override
            public T read(JsonReader in) throws IOException {
                return delegate.read(in);
            }
        };
    }
}

对于JSON应用程序打印上方的有效负载:

{
  "age": 22.0,
  "attributes": {
    "COMMERCIALNAME_E": "SADD MAARAB PHARMACY",
    "FACILITYSUBTYPE": "24 Hr Pharmacy",
    "FACILITYTYPE": "Pharmacy",
    "OBJECTID": "35"
  },
  "foods": [
    {
      "price": 100.0,
      "product": "apple"
    },
    {
      "fruit": "banana",
      "price": 100.0
    }
  ],
  "name": "John"
}