我无法完全理解反射的工作原理,因此尝试为GsonBuilder
注册自定义类型适配器时遇到了一些麻烦。
我需要为List<Something>
类型注册类型适配器。
这是一个工作代码:
gsonBuilder.registerTypeAdapter(
new TypeToken<List<MyClass>>() { }.getType(), new ListDeserializer(MyClass.class)
);
问题是我有很多类来注册我的类型适配器,并且我有一个
ListDeserializer
和SingleDeserializer
适配器。我试图变得通用,所以我只调用一个函数,传递我的
GsonBuilder
和类,然后就可以了。这是我的尝试:
private static <T> void registerTypeAdapter(GsonBuilder gsonBuilder, T clazz) {
gsonBuilder.registerTypeAdapter(clazz.getClass(), new SingleDeserializer(clazz.getClass()));
gsonBuilder.registerTypeAdapter(
new TypeToken<List<T>>() {
}.getType(), new ListDeserializer(clazz.getClass())
);
}
它对我的
ListDeserializer
不起作用。我的猜测是,由于T
是List
的通用参数化类型,因此无法在运行时检测到它。有什么建议么?
最佳答案
是的,由于泛型type erasure,您不能在运行时使用new TypeToken<List<T>>() {}.getType()
。 List<T>
在运行时只是List<Object>
。但是您可以做的是创建ParameterizedType
并使用如下代码:
Type type = ParameterizedTypeImpl.make(List.class, new Type[]{clazz.getClass()}, null);
gsonBuilder.registerTypeAdapter(type, new ListDeserializer(clazz.getClass()) );
但是,您真的需要泛型吗?你可以做
private static void registerTypeAdapter2(GsonBuilder gsonBuilder, Class<?> clazz) {
gsonBuilder.registerTypeAdapter(clazz, new SingleDeserializer());
Type type = ParameterizedTypeImpl.make(List.class, new Type[]{clazz}, null);
gsonBuilder.registerTypeAdapter(type, new ListDeserializer());
}
这是演示:
import com.google.gson.*;
import com.google.gson.annotations.SerializedName;
import com.google.gson.reflect.TypeToken;
import sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
public class Main {
public static void main(String[] args) throws Exception {
GsonBuilder gb = new GsonBuilder();
registerTypeAdapter(gb, MyClass.class);
Gson gson = gb.create();
List data = new ArrayList<>();
data.add(new MyClass("Bob"));
data.add(new MyClass("Alice"));
String listString = gson.toJson(data);
String soloString = gson.toJson(new MyClass("Test"));
Object resultList = gson.fromJson(listString, new TypeToken<List<MyClass>>() {}.getType());
Object resultSolo = gson.fromJson(soloString, MyClass.class);
System.out.println("RESULT:");
System.out.println("FROM " + listString +" TO "+ resultList);
System.out.println("FROM " + soloString +" TO "+ resultSolo);
}
private static void registerTypeAdapter(GsonBuilder gsonBuilder, Class<?> clazz) {
gsonBuilder.registerTypeAdapter(clazz, new SingleDeserializer());
Type type = ParameterizedTypeImpl.make(List.class, new Type[]{clazz}, null);
gsonBuilder.registerTypeAdapter(type, new ListDeserializer());
}
private static class ListDeserializer implements JsonDeserializer {
private static Gson gson = new Gson();
@Override
public Object deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
System.out.println("Used ListDeserializer: Type " + typeOfT);
Type t = (typeOfT instanceof ParameterizedType) ?
((ParameterizedType) typeOfT).getActualTypeArguments()[0] :
Object.class;
Type type = ParameterizedTypeImpl.make(List.class, new Type[]{t}, null);
List list = gson.fromJson(json, type);
return list;
}
}
private static class SingleDeserializer implements JsonDeserializer {
private static Gson gson = new Gson();
@Override
public Object deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
System.out.println("Used SingleDeserializer: Type " + typeOfT);
return gson.fromJson(json, typeOfT);
}
}
public static class MyClass {
@SerializedName("name")
private String name;
public MyClass(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "MyClass{" +
"name='" + name + '\'' +
'}';
}
}
}