JSON Serialize / Deserialize generic type with google-gson

Question

Well, I have to confess I'm not good at generic type in Java

I've written a JSON serialize/deserialize class in C# using JavaScriptSerializer

    private static JavaScriptSerializer js = new JavaScriptSerializer();

    public static T LoadFromJSONString<T>(string strRequest)
    {
        return js.Deserialize<T>(strRequest);
    }

    public static string DumpToJSONString<T>(T rq)
    {
        return js.Serialize(rq);
    }

It works well in C#. Now I'm trying to convert, or atleast, write another JSON serialize/deserialize class in Java. I've tried flexjson and google-gson but I don't know how to specify <T> in Java.

Could someone here help me? Btw, I prefer google-gson

StaxMan · Accepted Answer · 2010-11-19 15:52:11Z

9

+50

In Java you must pass actual type-erased class, not just type parameter, so data binders know what type to use; so something like:

public static T LoadFromJSONString<T>(string strRequest, Class<T> type)
{
    Gson gson = new Gson();
    return gson.fromJson(strRequest, type);
}

but this is usually just needed for deserialization; when serializing, you have an instance with a class which libraries can use.

Btw, one other good Java JSON library you might want to consider using is Jackson; however, for this particular example all libraries you mention should work.

answered Nov 19, 2010 at 15:52

StaxMan

117k35 gold badges215 silver badges241 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Tuan Anh Hoang-Vu Over a year ago

Hmm, but suppose I only have class info as string, for example String clazz = "com.example.Response", so how can I use this code?

StaxMan Over a year ago

You can use Class.forName("com.example.Response") to find it.

Tuan Anh Hoang-Vu Over a year ago

Yes, I've already tried. But the thing is that, when I use Class.forName(), the return type must be Object instead of Response, which I have to state clearly like this: Response rp = (Response) LoadFromJSONString(resString, Class.forName("com.example.Response"))

StaxMan Over a year ago

Since Class.forName() returns a Class<?>, you do need to do some casting; but while ugly, this does not prevent it from working. Interfaces typically require type parameter so that explicit passing of classes (Response.class is of type Class<Response>) is compatible with type parameter; but it is more of a nice to have feature. So you must pass the Class to bind to; type parameter T is not enough for Java to figure out actual real type.

Fredrik Wallenius · Accepted Answer · 2010-11-19 10:43:04Z

1

After thinking this through I don't think there is a way to solve this as pretty as it is done in your C# code. This because of the type erasure done by the java compiler.

The best solution for you would probably be to use the Gson object at the location where you know the type of the object you need to serialize/deserialize.

If you're not keen on making instances of the Gson object everytime you can of course keep that one static at least, since it doesn't need any type parameters when created.

answered Nov 19, 2010 at 10:43

Fredrik Wallenius

2,8822 gold badges22 silver badges16 bronze badges

Comments

Fredrik Wallenius · Accepted Answer · 2010-11-19 09:59:54Z

-1

This should work:

import com.google.gson.Gson;
public class GenericClass {

    private static Gson gson = new Gson(); 

    public static <T> T loadFromJSONString(String strRequest)
    {
        return (T) gson.fromJson(strRequest, T.class);
    }

    public static <T> String dumpToJSONString(T rq)
    {
        return gson.toJson(rq);
    }
}

edited Nov 19, 2010 at 9:59

answered Nov 19, 2010 at 9:45

Fredrik Wallenius

2,8822 gold badges22 silver badges16 bronze badges

1 Comment

Fredrik Wallenius Over a year ago

Hmm, wait. That won't work. This line causes problems: return (T) gson.fromJson(strRequest, T.class);

Collectives™ on Stack Overflow

JSON Serialize / Deserialize generic type with google-gson

3 Answers 3

4 Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related