根据JSON字段的值，具有不同类型对象的Gson流API

Question

I'm trying to parse the Wikidata JSON dump using the Gson streaming API, since the file is around 70GB of json. The overall structure of the file is as follows:

[
{"type":"item",... other fields ...},
{"type":"property",... other fields ...},
.....
]

It is an array of objects in which each object can be of type item or property and I would like to instantiate a different class (namely I have a corresponding Item and Property class in my Java code) according to the object that I encounter.

Basically, I'd like to look at the type field and then parse the following JSON accordingly. Since the JsonReader doesn't seem to provide a getNextJsonObject() or similar function, is there a way to do this besides preprocessing the whole file and splitting the entries into two separate ones? The file is so big that I'd like to avoid the extra preprocessing step when I could do everything on the fly.

Answer 1

I actually found a very easy solution after a bit of thinking. The Gson API provides the method:

Gson.fromJson(JsonReader reader, Class class)

This will read the next object from the reader and deserialize to the class you pass as parameter. Since in my case I don't know which class to serialize to I can do the following:

JsonObject asd = gson.fromJson(reader, JsonObject.class);
if (asd.get("type").getAsString().equals("item")) {
    // Instantiate item
} else {
    // Instantiate property
}