@Override
            public void serialize(Date date,
                                  JsonGenerator jsonGenerator,
                                  SerializerProvider serializerProvider) throws
                                                                         IOException {
                jsonGenerator.writeString(FORMATTER.print(new DateTime(date, DateTimeZone.UTC)));
            }
Contains Jackson module for serializing dates to ISO8601 format per the <a href="https://states-language.net/spec.html#timestamps">spec</a>.
aws-java-sdk-stepfunctions/src/main/java/com/amazonaws/services/stepfunctions/builder/internal/DateModule.java