The biggest change is that we no longer support Java 7. People who still need to run on Java 7 will need to use an earlier version of Gson.
Other changes:
Allow registering adapters for JsonElement again by @Marcono1234 in https://github.com/google/gson/pull/2789
Add nesting limit for JsonReader by @Marcono1234 in https://github.com/google/gson/pull/2588
Add @CheckReturnValue to our packages. by @cpovirk in https://github.com/google/gson/pull/2693
Add NullSafeTypeAdapter to prevent TypeAdapter.nullSafe() from returning nested null-safe type adapters (#2729) by @lyubomyr-shaydariv in https://github.com/google/gson/pull/2731
Support Properties subclasses in GsonTypes.getMapKeyAndValueTypes by @panic08 in https://github.com/google/gson/pull/2758
Enforce rawType to be a Class in ParameterizedTypeImpl by @panic08 in https://github.com/google/gson/pull/2759
Remove AccessController usage for enum adapter by @Marcono1234 in https://github.com/google/gson/pull/2704
Fix typeArguments array not being cloned when resolving ParameterizedType with changed owner by @TBlueF in https://github.com/google/gson/pull/2706
Remove duplicated declaration of required OSGi execution environment by @HannesWell in https://github.com/google/gson/pull/2711
Move bnd.bnd file configuration into 'bnd' element of bnd-maven-plugin by @HannesWell in https://github.com/google/gson/pull/2712
Move enum and JsonElement adapter classes to separate class files by @Marcono1234 in https://github.com/google/gson/pull/2727
EnumTypeAdapter constructor optimization by @esaulpaugh in https://github.com/google/gson/pull/2734
OSGi / bnd: Remove the self-Import of gson.annotations by @chrisrueger in https://github.com/google/gson/pull/2735
New Contributors
@cpovirk made their first contribution in https://github.com/google/gson/pull/2693
@jabagawee made their first contribution in https://github.com/google/gson/pull/2701
@TBlueF made their first contribution in https://github.com/google/gson/pull/2706
@HannesWell made their first contribution in https://github.com/google/gson/pull/2711
@esaulpaugh made their first contribution in https://github.com/google/gson/pull/2734
@chrisrueger made their first contribution in https://github.com/google/gson/pull/2735
@panic08 made their first contribution in https://github.com/google/gson/pull/2756
Full Changelog: https://github.com/google/gson/compare/gson-parent-2.11.0...gson-parent-2.12.0