具有动态 ArrayList 项类型的 Gson TypeToken

The syntax you are proposing is invalid. The following

new TypeToken<ArrayList<Class.forName(MyClass)>>

is invalid because you're trying to pass a method invocation where a type name is expected.

The following

new TypeToken<ArrayList<T>>()

is not possible because of how generics (type erasure) and reflection works. The whole TypeToken hack works because Class#getGenericSuperclass() does the following

Returns the Type representing the direct superclass of the entity (class, interface, primitive type or void) represented by this Class.

If the superclass is a parameterized type, the Type object returned must accurately reflect the actual type parameters used in the source code.

In other words, if it sees ArrayList<T>, that's the ParameterizedType it will return and you won't be able to extract the compile time value that the type variable T would have had.

Type and ParameterizedType are both interfaces. You can provide an instance of your own implementation (define a class that implements either interface and overrides its methods) or use one of the helpful factory methods that TypeToken provides in its latest versions. For example,

private Type setModelAndGetCorrespondingList2(Class<?> typeArgument) {
return TypeToken.getParameterized(ArrayList.class, typeArgument).getType();
}

This worked for me:

public <T> List<T> listEntity(Class<T> clazz)
throws WsIntegracaoException {
try {
// Consuming remote method
String strJson = getService().listEntity(clazz.getName());


JsonParser parser = new JsonParser();
JsonArray array = parser.parse(strJson).getAsJsonArray();


List<T> lst =  new ArrayList<T>();
for(final JsonElement json: array){
T entity = GSON.fromJson(json, clazz);
lst.add(entity);
}


return lst;


} catch (Exception e) {
throw new WsIntegracaoException(
"WS method error [listEntity()]", e);
}
}

Option 1 - implement java.lang.reflect.ParameterizedType yourself and pass it to Gson.

private static class ListParameterizedType implements ParameterizedType {


private Type type;


private ListParameterizedType(Type type) {
this.type = type;
}


@Override
public Type[] getActualTypeArguments() {
return new Type[] {type};
}


@Override
public Type getRawType() {
return ArrayList.class;
}


@Override
public Type getOwnerType() {
return null;
}


// implement equals method too! (as per javadoc)
}

Then simply:

Type type = new ListParameterizedType(clazz);
List<T> list = gson.fromJson(json, type);

Note that as per javadoc, equals method should also be implemented.

Option 2 - (don't do this) reuse gson internal...

This will work too, at least with Gson 2.2.4.

Type type = com.google.gson.internal.$Gson$Types.newParameterizedTypeWithOwner(null, ArrayList.class, clazz);

You can actually do it. You just need to parse first your data into an JsonArray and then transform each object individually, and add it to a List :

Class<T> dataType;


//...


JsonElement root = jsonParser.parse(json);
List<T> data = new ArrayList<>();
JsonArray rootArray = root.getAsJsonArray();
for (JsonElement json : rootArray) {
try {
data.add(gson.fromJson(json, dataType));
} catch (Exception e) {
e.printStackTrace();
}
}
return data;

sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl workes. No need for custom implementation

Type type = ParameterizedTypeImpl.make(List.class, new Type[]{childrenClazz}, null);
List list = gson.fromJson(json, type);

Can be used with maps and any other collection:

ParameterizedTypeImpl.make(Map.class, new Type[]{String.class, childrenClazz}, null);

Here is nice demo how you can use it in custom deserializer: Deserializing ImmutableList using Gson

You can do this with Guava's more powerful TypeToken:

private static <T> Type setModelAndGetCorrespondingList2(Class<T> type) {
return new TypeToken<ArrayList<T>>() {}
.where(new TypeParameter<T>() {}, type)
.getType();
}

Since Gson 2.8.0, you can use TypeToken#getParameterized(Type rawType, Type... typeArguments) to create the TypeToken, then getType() should do the trick.

For example:

TypeToken.getParameterized(ArrayList.class, myClass).getType()

Fully working solution:

String json = .... //example: mPrefs.getString("list", "");
ArrayList<YouClassName> myTypes = fromJSonList(json, YouClassName.class);




public <YouClassName> ArrayList<YouClassName> fromJSonList(String json, Class<YouClassName> type) {
Gson gson = new Gson();
return gson.fromJson(json, TypeToken.getParameterized(ArrayList.class, type).getType());
}

With kotlin you can use a below functions to converting (from/to) any (JsonArray/JsonObject) just in one line without need to send a TypeToken :-

Convert any class or array to JSON string

inline fun <reified T : Any> T?.json() = this?.let { Gson().toJson(this, T::class.java) }

Example to use :

 val list = listOf("1","2","3")
val jsonArrayAsString = list.json()
//output : ["1","2","3"]


val model= Foo(name = "example",email = "t@t.com")
val jsonObjectAsString = model.json()
//output : {"name" : "example", "email" : "t@t.com"}

Convert JSON string to any class or array

inline fun <reified T : Any> String?.fromJson(): T? = this?.let {
val type = object : TypeToken<T>() {}.type
Gson().fromJson(this, type)
}

Example to use :

 val jsonArrayAsString = "[\"1\",\"2\",\"3\"]"
val list = jsonArrayAsString.fromJson<List<String>>()


val jsonObjectAsString = "{ "name" : "example", "email" : "t@t.com"}"
val model : Foo? = jsonObjectAsString.fromJson()
//or
val model = jsonObjectAsString.fromJson<Foo>()

in kotlin you can

inline fun <reified T> parseData(row :String): T{
return Gson().fromJson(row, object: TypeToken<T>(){}.type)
}

Well actually i have made extension functions to resolve this , saving a list to SharedPrefrence and retrieve them in anyplace in the app like this :

use this to Save a List to SharedPref. For example :

fun <T> SaveList(key: String?, list: List<T>?) {
val gson = Gson()
val json: String = gson.toJson(list)
getSharedPrefrences(App.getAppContext() as Application).edit().putString(key, json).apply()}

return the list in any place from sharedPref. like this :

fun Context.getList(key: String): String? {
return getSharedPrefrences(App.getAppContext() as Application).getString(key, null)}


inline fun <reified T : Any> String?.fromJson(): T? = this?.let {
val type = object : TypeToken<T>() {}.type
Gson().fromJson(this, type)}

Usage in Saving and Getting List from Saved one is like :

saveList(Consts.SLIDERS, it.data)


SetSliderData(this.getList(Consts.SLIDERS).fromJson<MutableList<SliderResponseItem>>()!!)

This is straightforward & simple in Kotlin.

val typeDataModelClass = Array<DataModelClass>::class.java

  this code is json string data to convert in arraylist model








String json = getIntent().getExtras().getString("submitQuesList", "");
Type typeOfObjectsList = new TypeToken<ArrayList<Datum_ques>>() {
}.getType();
submitQuesList = new Gson().fromJson(json, typeOfObjectsList);