CODEWITHSUNDEEP
javajsongson
Moshe Shaham
Moshe Shaham

Reputation: 15984

Deserialize JSON list of objects when the class is known at run time

I have a function that receives as parameter a json string and a class name as string of an object. The json is really a list of this object. I'm trying to create the list from the json but I'm unsuccessful.

Here is how I decode the json when the class name is known at compile time:

Type listOfObjects = new TypeToken<List<UsernamePart>>(){}.getType();
Gson gson = new Gson();
List<UsernamePart> parts = gson.fromJson(input, listOfObjects);

That works perfectly. But what happens if I want to do something like this:

// I have a string
String className = "UsernamePart";
// I can easily create a class object
Class<?> clazz = Class.forName(className); 
// and now what?
Type listOfObjects = new TypeToken<List<??????????>>(){}.getType();
Gson gson = new Gson();
List<UsernamePart> parts = gson.fromJson(input, listOfObjects);

Upvotes: 4

Views: 439

Answers (2)

raylu
raylu

Reputation: 2814

String className = "UsernamePart";
Class<?> genericClass = Class.forName(className);
Class arrayClass = java.lang.reflect.Array.newInstance(genericClass, 0).getClass();
Object[] array = (Object[]) new Gson().fromJson(input, arrayClass);
List parts = com.google.common.collect.Lists.newArrayList(array);

Upvotes: 3

user3569285
user3569285

Reputation:

Unfortunately you can not parameterize a Generic at runtime. The type must always been known at compile time.

Upvotes: 0

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