問題
I want to make gson able to return an EnumMap object. I use the following code
map子類、package sandbox;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
javamap原理?import java.util.EnumMap;
import java.util.Map;
/**
hashmap的實現,*
* @author yccheok
*/
gson使用,public class Sandbox {
public static void main(String[] args) throws InterruptedException {
testGson();
map.getOrDefault?}
public static enum Country {
Malaysia,
hashMap。UnitedStates
}
public static void testGson() {
Map enumMap = new EnumMap(Country.class);
enumMap.put(Country.Malaysia, "RM");
enumMap.put(Country.UnitedStates, "USD");
Gson gson = new Gson();
String string = gson.toJson(enumMap);
System.out.println("toJSon : " + string);
enumMap = gson.fromJson(string, new TypeToken>(){}.getType());
System.out.println("fromJSon : " + enumMap);
System.out.println("fromJSon : " + enumMap.getClass());
}
}
However, I'm getting the following
toJSon : {"Malaysia":"RM","UnitedStates":"USD"}
fromJSon : {Malaysia=RM, UnitedStates=USD}
fromJSon : class java.util.LinkedHashMap
even though I had used new TypeToken>(){}.getType() to specific I want EnumMap instead of LinkedHashMap
How can I make gson to return EnumMap?
回答1:
Even with a type token, Gson can only deserialize data into classes that have a default constructor. And EnumMap doesn't have one (it needs to be instantiated with the type of enum that its elements will match). The easiest way around this problem is to define and use an InstanceCreator:
This interface is implemented to create instances of a class that does not define a no-args constructor. If you can modify the class, you should instead add a private, or public no-args constructor. However, that is not possible for library classes, such as JDK classes, or a third-party library that you do not have source-code of. In such cases, you should define an instance creator for the class. Implementations of this interface should be registered with GsonBuilder.registerTypeAdapter(Type, Object) method before Gson will be able to use them.
Heres some example code:
InstanceCreator:
class EnumMapInstanceCreator, V> implements
InstanceCreator> {
private final Class enumClazz;
public EnumMapInstanceCreator(final Class enumClazz) {
super();
this.enumClazz = enumClazz;
}
@Override
public EnumMap createInstance(final Type type) {
return new EnumMap(enumClazz);
}
}
Test code:
final Gson gson = new GsonBuilder().registerTypeAdapter(
new TypeToken>() {
}.getType(),
new EnumMapInstanceCreator(Country.class))
.create();
final Map enumMap = new EnumMap(
Country.class);
enumMap.put(Country.Malaysia, "RM");
enumMap.put(Country.UnitedStates, "USD");
String string = gson.toJson(enumMap);
System.out.println("toJSon : " + string);
final Map reverseEnumMap = gson.fromJson(string,
new TypeToken>() {
}.getType());
System.out.println("fromJSon (Class): " + reverseEnumMap.getClass());
System.out.println("fromJSon : " + reverseEnumMap);
來源:https://stackoverflow.com/questions/16127904/gson-fromjson-return-linkedhashmap-instead-of-enummap
版权声明:本站所有资料均为网友推荐收集整理而来,仅供学习和研究交流使用。
工作时间:8:00-18:00
客服电话
电子邮件
admin@qq.com
扫码二维码
获取最新动态