Question

我使用Moshi，我需要使用越野车解决我的问题。有时，当我请求对象列表时，其中一些不包含必填字段。当然，我可以捕获并处理JsonDataException，但是我想跳过这些对象。我如何用Moshi做到这一点？

更新

我有几种完成任务的模型

@JsonClass(generateAdapter = true)
data class User(
        val name: String,
        val age: Int?
)

@JsonClass(generateAdapter = true)
data class UserList(val list: List<User>)

和错误的JSON

{
  "list": [
    {
      "name": "John",
      "age": 20
    },
    {
      "age": 18
    },
    {
      "name": "Jane",
      "age": 21
    }
  ]
}

如您所见，第二个对象没有必填name字段，我想通过Moshi适配器跳过它。

Answer 1

似乎我找到了答案

class SkipBadListObjectsAdapterFactory : JsonAdapter.Factory {
    override fun create(type: Type, annotations: MutableSet<out Annotation>, moshi: Moshi): JsonAdapter<*>? {
        return if (annotations.isEmpty() && Types.getRawType(type) == List::class.java) {
            val elementType = Types.collectionElementType(type, List::class.java)
            val elementAdapter = moshi.adapter<Any>(elementType)

            SkipBadListObjectsAdapter(elementAdapter)
        } else {
            null
        }
    }

    private class SkipBadListObjectsAdapter<T : Any>(private val elementAdapter: JsonAdapter<T>) :
        JsonAdapter<List<T>>() {
        override fun fromJson(reader: JsonReader): List<T>? {
            val goodObjectsList = mutableListOf<T>()

            reader.beginArray()

            while (reader.hasNext()) {
                try {
                    elementAdapter.fromJson(reader)?.let(goodObjectsList::add)
                } catch (e: JsonDataException) {
                    // Skip bad element ;)
                }
            }

            reader.endArray()

            return goodObjectsList

        }

        override fun toJson(writer: JsonWriter, value: List<T>?) {
            throw UnsupportedOperationException("SkipBadListObjectsAdapter is only used to deserialize objects")
        }
    }
}

谢谢“其他主题的人” =）

Answer 2

解决方案中有一个陷阱，只有在失败后才能捕获并忽略。例如，如果您的元素适配器在发生错误后停止读取，则读取器可能正在读取嵌套对象，而下一个hasNext调用将在错误的位置被调用。

正如杰西所说，您可以窥视并跳过整个值。

class SkipBadElementsListAdapter(private val elementAdapter: JsonAdapter<Any?>) :
    JsonAdapter<List<Any?>>() {
  object Factory : JsonAdapter.Factory {
    override fun create(type: Type, annotations: Set<Annotation>, moshi: Moshi): JsonAdapter<*>? {
      if (annotations.isNotEmpty() || Types.getRawType(type) != List::class.java) {
        return null
      }
      val elementType = Types.collectionElementType(type, List::class.java)
      val elementAdapter = moshi.adapter<Any?>(elementType)
      return SkipBadElementsListAdapter(elementAdapter)
    }
  }

  override fun fromJson(reader: JsonReader): List<Any?>? {
    val result = mutableListOf<Any?>()
    reader.beginArray()
    while (reader.hasNext()) {
      try {
        val peeked = reader.peekJson()
        result += elementAdapter.fromJson(peeked)
      } catch (ignored: JsonDataException) {
      }
      reader.skipValue()
    }
    reader.endArray()
    return result

  }

  override fun toJson(writer: JsonWriter, value: List<Any?>?) {
    if (value == null) {
      throw NullPointerException("value was null! Wrap in .nullSafe() to write nullable values.")
    }
    writer.beginArray()
    for (i in value.indices) {
      elementAdapter.toJson(writer, value[i])
    }
    writer.endArray()
  }
}

Moshi适配器跳过List <t>中的不良对象

2 个答案: