gson 下划线转驼峰

可以通过自定义 `JsonDeserializer` 来实现将下划线转换为驼峰的功能。以下是一个示例代码：

import com.google.gson.*;

import java.lang.reflect.Type;

public class UnderlineToCamelDeserializer<T> implements JsonDeserializer<T> {

    private static final String UNDERLINE = "_";

    @Override
    public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        JsonObject jsonObject = json.getAsJsonObject();
        return new Gson().fromJson(underlineToCamel(jsonObject), typeOfT);
    }

    private JsonObject underlineToCamel(JsonObject jsonObject) {
        JsonObject result = new JsonObject();
        for (String key : jsonObject.keySet()) {
            JsonElement value = jsonObject.get(key);
            String camelKey = underlineToCamel(key);
            if (value.isJsonObject()) {
                result.add(camelKey, underlineToCamel(value.getAsJsonObject()));
            } else if (value.isJsonArray()) {
                result.add(camelKey, underlineToCamel(value.getAsJsonArray()));
            } else {
                result.add(camelKey, value);
            }
        }
        return result;
    }

    private JsonArray underlineToCamel(JsonArray jsonArray) {
        JsonArray result = new JsonArray();
        for (JsonElement jsonElement : jsonArray) {
            if (jsonElement.isJsonObject()) {
                result.add(underlineToCamel(jsonElement.getAsJsonObject()));
            } else if (jsonElement.isJsonArray()) {
                result.add(underlineToCamel(jsonElement.getAsJsonArray()));
            } else {
                result.add(jsonElement);
            }
        }
        return result;
    }

    private String underlineToCamel(String str) {
        StringBuilder sb = new StringBuilder();
        boolean flag = false;
        for (char c : str.toCharArray()) {
            if (c == '_') {
                flag = true;
            } else {
                if (flag) {
                    sb.append(Character.toUpperCase(c));
                    flag = false;
                } else {
                    sb.append(c);
                }
            }
        }
        return sb.toString();
    }

}

然后在使用 `Gson` 解析 JSON 时，将自定义的 `JsonDeserializer` 传入即可：

Gson gson = new GsonBuilder()
        .registerTypeAdapter(MyClass.class, new UnderlineToCamelDeserializer<>())
        .create();
MyClass myClass = gson.fromJson(jsonString, MyClass.class);