Gson ignore null when deserializing object

问题

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"}

When I deserialize using

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

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?

回答1:

We have this solution:

1. All of your data classes need to extends abstract class

abstract class PoJoClass

2. Create this safe deserializer to delete nulls from JSON

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. And register it in your GSON instance

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

回答2:

See http://sites.google.com/site/gson/gson-user-guide#TOC-Null-Object-Support:

Gson gson = new GsonBuilder().serializeNulls().create();

来源：https://stackoverflow.com/questions/33301036/gson-ignore-null-when-deserializing-object

标签

java

json

gson

deserialization