HashMap的序列化和反序列化<MyObject, List<Integer> 与杰克逊

Question

I am currently working on a small android app that needs to be able to save/restore a range of settings via serialization/deserialization using the Jackson lib. For most parts it works really well and I can serialize my objects and restore them again. Now I need to serialize/deserialize private member with the type:

HashMap<Model, List<Integer>>

Model being one of my own objects containing a bunch of simple values + getter/setter methods. And this is where I run into problems. It starts throwing the following error at me:

DataAccess: Cannot find a (Map) Key deserializer for type [simple type, class com.schulz.toolie.Models.Model] at [Source: (String)"{"; line: 1, column: 1]

I have tried setting annotations like @JsonAnyGetter and @JsonAnySetter on the getter/setter methods along with the @JsonProperty("subscribe") on both the getter, setter and variable.

Is there any way to get around this? preferably without writing custom serialization/deserialization methods as I will get quite a few of these.

Answer 1

Your problem is that Jackson has a standard for converting a Map to JSON. The keys of the map are used as the property names in the results JSON.

Map<String, Double> groceryPrices = new HashMap<>();
groceryPrices.put("apple", 0.25);
groceryPrices.put("orange", 0.30);

This naturally translates to a JSON object:

{
  "apple": 0.25,
  "orange": 0.30
}

The problem is you are using a complex object to represent a key. There is no simple method for serializing and deserializing your complex object to/from a String.

If you don't want to write custom serialization, I suggest you change your data structure. Your current structure ties together a model with it's Integers. You could fold the list of Integers into the Model object itself:

Map<String, Model> models; // This could map modelId -> Model which now contains the integers