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How can I convert JSON to a HashMap using Gson?

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臣服心动 2020-11-22 05:14

I\'m requesting data from a server which returns data in the JSON format. Casting a HashMap into JSON when making the request wasn\'t hard at all but the other way seems to

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  • 萌比男神i
    萌比男神i (楼主)
    2020-11-22 05:58

    I know this is a fairly old question, but I was searching for a solution to generically deserialize nested JSON to a Map, and found nothing.

    The way my yaml deserializer works, it defaults JSON objects to Map when you don't specify a type, but gson doesn't seem to do this. Luckily you can accomplish it with a custom deserializer.

    I used the following deserializer to naturally deserialize anything, defaulting JsonObjects to Map and JsonArrays to Object[]s, where all the children are similarly deserialized.

    private static class NaturalDeserializer implements JsonDeserializer {
  public Object deserialize(JsonElement json, Type typeOfT, 
      JsonDeserializationContext context) {
    if(json.isJsonNull()) return null;
    else if(json.isJsonPrimitive()) return handlePrimitive(json.getAsJsonPrimitive());
    else if(json.isJsonArray()) return handleArray(json.getAsJsonArray(), context);
    else return handleObject(json.getAsJsonObject(), context);
  }
  private Object handlePrimitive(JsonPrimitive json) {
    if(json.isBoolean())
      return json.getAsBoolean();
    else if(json.isString())
      return json.getAsString();
    else {
      BigDecimal bigDec = json.getAsBigDecimal();
      // Find out if it is an int type
      try {
        bigDec.toBigIntegerExact();
        try { return bigDec.intValueExact(); }
        catch(ArithmeticException e) {}
        return bigDec.longValue();
      } catch(ArithmeticException e) {}
      // Just return it as a double
      return bigDec.doubleValue();
    }
  }
  private Object handleArray(JsonArray json, JsonDeserializationContext context) {
    Object[] array = new Object[json.size()];
    for(int i = 0; i < array.length; i++)
      array[i] = context.deserialize(json.get(i), Object.class);
    return array;
  }
  private Object handleObject(JsonObject json, JsonDeserializationContext context) {
    Map map = new HashMap();
    for(Map.Entry entry : json.entrySet())
      map.put(entry.getKey(), context.deserialize(entry.getValue(), Object.class));
    return map;
  }
}



    The messiness inside the handlePrimitive method is for making sure you only ever get a Double or an Integer or a Long, and probably could be better, or at least simplified if you're okay with getting BigDecimals, which I believe is the default.
    


    You can register this adapter like:
    


    GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(Object.class, new NaturalDeserializer());
Gson gson = gsonBuilder.create();

    


    And then call it like:
    


    Object natural = gson.fromJson(source, Object.class);

    


    I'm not sure why this is not the default behavior in gson, since it is in most other semi-structured serialization libraries...
    
    
    
             
    
                                                        
    
            
            
    
              
                
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