What's new in GSON 2.0

GSON 1.x used to automatically unwrap single-element arrays as necessary.
GSON 2.x doesn't.
com.google.gson.functional.ArrayTest.testSingleStringArrayDeserialization
com.google.gson.functional.PrimitiveTest#testPrimitiveIntegerAutoboxedInASingleElementArrayDeserialization
com.google.gson.functional.PrimitiveTest#testPrimitiveLongAutoboxedInASingleElementArrayDeserialization
com.google.gson.functional.PrimitiveTest#testPrimitiveBooleanAutoboxedDeserialization
com.google.gson.functional.PrimitiveTest.testPrimitiveBooleanAutoboxedInASingleElementArrayDeserialization
com.google.gson.functional.PrimitiveTest.testPrimitiveDoubleAutoboxedInASingleElementArrayDeserialization
com.google.gson.functional.PrimitiveTest.testBigDecimalInASingleElementArrayDeserialization
com.google.gson.functional.PrimitiveTest.testBigIntegerInASingleElementArrayDeserialization
com.google.gson.functional.StringTest.testStringValueAsSingleElementArrayDeserialization
com.google.gson.functional.EnumTest.testTopLevelEnumInASingleElementArrayDeserialization

GSON 1.x permitted primitive types to be overridden
GSON 2.x doesn't.
com.google.gson.functional.ArrayTest.testArrayOfPrimitivesWithCustomTypeAdapter
com.google.gson.functional.PrimitiveTest.testOverridingDefaultPrimitiveSerialization


GSON 1.x rejects integers that have any fraction, even if it is ".0"
GSON 2.x permits integers to have ".0" fractions like "1.0"
com.google.gson.functional.PrimitiveTest.testDeserializingDecimalPointValuesAsIntegerFails

GSON 1.x truncates oversized large integers and longs
GSON 2.x fails on oversized large integers and longs
com.google.gson.functional.PrimitiveTest.testDeserializingBigIntegerAsInteger
com.google.gson.functional.PrimitiveTest.testDeserializingBigIntegerAsLong


GSON 1.x uses arbitrary precision for primitive type conversion (so -122.08e-2132 != 0)
GSON 2.x uses double precision (so -122.08e-2132 == 0)
com.google.gson.functional.PrimitiveTest.testDeserializingBigDecimalAsLongFails


GSON 1.x supports type adapters for primitive types
GSON 2.x doesn't
com.google.gson.functional.CustomTypeAdaptersTest.testCustomSerializerForLong
com.google.gson.functional.CustomTypeAdaptersTest.testCustomDeserializerForLong


GSON 1.x throws IllegalStateException on circular references
GSON 2.x lets the runtime throw a StackOverflowError
com.google.gson.functional.CircularReferenceTest.testCircularSerialization
com.google.gson.functional.CircularReferenceTest.testSelfReferenceSerialization
com.google.gson.functional.CircularReferenceTest.testSelfReferenceArrayFieldSerialization
com.google.gson.functional.CircularReferenceTest.testSelfReferenceCustomHandlerSerialization


GSON 1.x sometimes sets subclass fields when an InstanceCreator returns a subclass.
    This occurs only when the value is a field of another object: not when its
    the top level object or a collection element.
GSON 2.x sets fields of the requested type only
com.google.gson.functional.InstanceCreatorTest.testInstanceCreatorReturnsSubTypeForField

GSON 1.x applies different rules for versioning for classes vs fields. So, if you deserialize a
   JSON into a field that is supposed to be skipped, the field is set to null (or default value). 
   However, if you deserialize it to a top-level class, a default instance is returned.
GSON 2.x returns null for the top-level class. 
com.google.gson.functional.VersioningTest.testIgnoreLaterVersionClassDeserialization