JDK 17: InaccessibleObjectException when deserialized class has java.time.Instant field

[Or4ng3]

Hi.

I'm using gson 2.8.8 with jdk 17. This code:

import com.google.gson.Gson;
import org.junit.jupiter.api.Test;

import java.time.Instant;

class DTO {
	private Instant instant;
}

public class GsonTest {
	@Test
	public void test() {
		var gson = new Gson();
		var dto = gson.fromJson("{}", DTO.class);
	}
}

Fails with exception:

java.lang.reflect.InaccessibleObjectException: Unable to make field private final long java.time.Instant.seconds accessible: module java.base does not "opens java.time" to unnamed module @73035e27

	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354)
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
	at java.base/java.lang.reflect.Field.checkCanSetAccessible(Field.java:178)
	at java.base/java.lang.reflect.Field.setAccessible(Field.java:172)
	at com.google.gson.internal.reflect.UnsafeReflectionAccessor.makeAccessible(UnsafeReflectionAccessor.java:44)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:159)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102)
	at com.google.gson.Gson.getAdapter(Gson.java:458)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102)
	at com.google.gson.Gson.getAdapter(Gson.java:458)
	at com.google.gson.Gson.fromJson(Gson.java:931)
	at com.google.gson.Gson.fromJson(Gson.java:897)
	at com.google.gson.Gson.fromJson(Gson.java:846)
	at com.google.gson.Gson.fromJson(Gson.java:817)
	at com.test.GsonTest.test(GsonTest.java:17)

[Marcono1234]

See #1979 (comment) or related issues. You are deserializing (maybe by accident) an internal field of a JDK class; you have to write a custom TypeAdapter or you could try third-party libraries such as https://github.com/gkopff/gson-javatime-serialisers adding support for java.time classes.

[Or4ng3]

Yes, the problem with class java.time.Instant (it's the only field in example). Also I see same problem with LocalDate and LocalTime classes.
However, I think that java.time package should be supported since its classes are newer and better than java.util.Date

[Marcono1234]

However, I think that java.time package should be supported since its classes are newer and better than java.util.Date

See #1059