Can't deserialized EnumMap with override toString()

Gson version

2.9.0

Java / Android version

JDK 17.0.2

Used tools

• Maven; version: 3.8.5

Description

When serialize EnumMap to Json, it has strange behavior that calls toString() instead of name() of enum key unlike when serialize the normal enum type do.

Expected behavior

{"single_fruit":"APPLE","multi_fruit":{"APPLE":3,"BANANA":2}}

Actual behavior

{"single_fruit":"APPLE","multi_fruit":{"Golden Apple":3,"Green Banana":2}}

Reproduction steps

See this simple program below.

import com.google.gson.Gson;

import java.util.EnumMap;
import java.util.ResourceBundle;


public class Main {

    public enum Fruit {
        APPLE,
        BANANA;
        private final ResourceBundle bundle = ResourceBundle.getBundle("Main");

        @Override
        public String toString() {
            return bundle.getString(this.name());
        }
    }
    public static class FruitData {
        public Fruit single_fruit;
        public EnumMap<Fruit, Integer> multi_fruit;
    }
    public static void main(String[] args) {
        Gson jsonParser = new Gson();
        FruitData f = new FruitData();
        f.single_fruit = Fruit.APPLE;
        f.multi_fruit = new EnumMap<>(Fruit.class);
        f.multi_fruit.put(Fruit.APPLE, 3);
        f.multi_fruit.put(Fruit.BANANA, 2);

        System.out.println(jsonParser.toJson(f));

        // it should be successful
        // System.out.println(jsonParser.fromJson(jsonParser.toJson(f), FruitData.class));
    }
}

Main.properties

APPLE=Golden Apple
BANANA=Green Banana

Exception stack trace

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "key" is null
	at java.base/java.util.EnumMap.typeCheck(EnumMap.java:736)
	at java.base/java.util.EnumMap.put(EnumMap.java:264)
	at java.base/java.util.EnumMap.put(EnumMap.java:78)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:188)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:130)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:221)
	at com.google.gson.Gson.fromJson(Gson.java:991)
	at com.google.gson.Gson.fromJson(Gson.java:956)
	at com.google.gson.Gson.fromJson(Gson.java:905)
	at com.google.gson.Gson.fromJson(Gson.java:876)
	at Main.main(Main.java:35)

TODO List

• Update README/User Guide to add enableComplexMapKeySerialization() things. (Fixed by #2138 )

[Evyde]

Have created #2138 now which also documents Map serialization and deserialization in general. You can see the rendered version here: https://github.com/Marcono1234/gson/blob/marcono1234/map-serialization-user-guide/UserGuide.md#TOC-Maps-Examples

I made this a separate PR and did not include it in any other PR to make it easier for the maintainers to review.

I reviewed this changed README and was extremely satisfied with it. Thanks for your working. This issue will be closed when this PR been merged.

[Marcono1234]

Have created #2138 now which also documents Map serialization and deserialization in general. You can see the rendered version here: https://github.com/Marcono1234/gson/blob/marcono1234/map-serialization-user-guide/UserGuide.md#TOC-Maps-Examples

I made this a separate PR and did not include it in any other PR to make it easier for the maintainers to review.