反序列化对象时，Gson会忽略null [英] Gson ignore null when deserializing object

问题描述

我想反序列化Java中包含空值的json字符串.我想将该对象反序列化为Properties对象. json字符串类似于:

I want to deserialize a json string that containts a null value in Java. I want to deserialize the object to a Properties object. The json string is something like:

{"prop1":null, "propr2":"fancy value"}

当我反序列化使用时

String json = //
new Gson().fromJson(json, Properties.class);

由于进入Properties对象的Hastable，我得到了空指针异常.如何指示Gson忽略空值的反序列化?

I get a null pointer exception because of the Hastable that into the Properties object. How can I instruct Gson to ignore deserialization of null values?

推荐答案

我们有以下解决方案:

1.您所有的数据类都需要扩展抽象类

abstract class PoJoClass

2.创建此安全的反序列化器以从JSON中删除空值

class SafeDeserializer<T : PoJoClass>(private val gson: Gson) :JsonDeserializer<T> {
    override fun deserialize(json: JsonElement?, typeOfT: Type?, context: JsonDeserializationContext?): T {

        val jsonObject = json as JsonObject
        removeNullsFromJson(jsonObject)
        return gson.fromJson(jsonObject, typeOfT)
    }

    private fun removeNullsFromJson(jsonObject: JsonObject) {
        val iterator = jsonObject.keySet().iterator()

        while (iterator.hasNext()) {
            val key = iterator.next()
            when(val json = jsonObject[key]){
                is JsonObject -> removeNullsFromJson(json)
                is JsonNull -> iterator.remove()
            }
        }
    }
}

3.并将其注册到您的GSON实例中

val gson = Gson().newBuilder()
                .registerTypeHierarchyAdapter(PoJoClass::class.java, SafeDeserializer<PoJoClass>(Gson()))
                .create()

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