Jackson - Deserialize using generic class

I have a json string, which I should deSerialize to the following class

class Data <T> {
    int found;
    Class<T> hits
}

How do I do it? This is the usual way

mapper.readValue(jsonString, Data.class);

But how do I mention what T stands for?

Solution 1:

You need to create a TypeReference object for each generic type you use and use that for deserialization. For example -

mapper.readValue(jsonString, new TypeReference<Data<String>>() {});

Solution 2:

You can't do that: you must specify fully resolved type, like Data<MyType>. T is just a variable, and as is meaningless.

But if you mean that T will be known, just not statically, you need to create equivalent of TypeReference dynamically. Other questions referenced may already mention this, but it should look something like:

public Data<T> read(InputStream json, Class<T> contentClass) {
   JavaType type = mapper.getTypeFactory().constructParametricType(Data.class, contentClass);
   return mapper.readValue(json, type);
}

Solution 3:

First thing you do is serialize, then you can do deserialize.
so when you do serialize, you should use @JsonTypeInfo to let jackson write class information into your json data. What you can do is like this:

Class Data <T> {
    int found;
    @JsonTypeInfo(use=JsonTypeInfo.Id.CLASS, include=JsonTypeInfo.As.PROPERTY, property="@class")
    Class<T> hits
}

Then when you deserialize, you will find jackson has deserialize your data into a class which your variable hits actually is at runtime.