Jackson 2 to 3 migration companion code

Three Maven modules - jackson2-before (2.22.1), jackson3-after (3.2.1) and a
coexistence module with BOTH majors on one classpath - so every claim in the two
migration guides is executed rather than asserted. Paired class names make the
before/after outputs directly diffable via run-all.sh.

Confirms the guides on wire-format equivalence (10-case suite, zero mismatches),
classpath coexistence and the collapse of four artifacts into one. Corrects nine
points, including that enableDefaultTyping() is still present in Jackson 2.22.1
rather than removed in 2.16, and that the published "after" mapper snippet does
not compile.

docs/output/after-S01MapperConstruction.txt

@@ -0,0 +1,4 @@
+output          : {"id":1,"travelDate":"2026-09-15","seatPreference":"aisle"}
+forked indented : { "id" : 1, "travelDate" : "2026-09-15", "seatPreference" : "aisle" }
+original intact : false
+set*() mutators : 0   <- mutation is impossible, not merely discouraged

docs/output/after-S02ExceptionHierarchy.txt

@@ -0,0 +1,5 @@
+JacksonException extends RuntimeException : true
+JacksonException extends IOException      : false
+ESCAPED catch (IOException)   : StreamReadException
+caught by catch (Jackson...)  : StreamReadException
+writeValueAsString declares   : [class tools.jackson.core.JacksonException]  <- nothing checked

docs/output/after-S03CustomHandlers.txt

@@ -0,0 +1,3 @@
+serialised   : {"amount":19.99,"currency":"USD"}
+deserialised : Money[amount=20.0, currencyCode=USD]
+base classes : tools.jackson.databind.ValueSerializer / tools.jackson.databind.ValueDeserializer

docs/output/after-S04ModulesAndRecords.txt

@@ -0,0 +1,4 @@
+no modules      : {"id":1,"departure":"2026-09-15","seat":"12A"}
+round-trip      : TravelPlan[id=1, departure=2026-09-15, seat=Optional[12A]]
+dates           : {"d":"2026-09-15"}
+empty Optional  : {"id":2,"departure":"2026-09-16","seat":null}

docs/output/after-S05DefaultTyping.txt

@@ -0,0 +1,7 @@
+enableDefaultTyping    on Jackson 3 ObjectMapper : false
+activateDefaultTyping  on Jackson 3 ObjectMapper : false
+activateDefaultTyping  on JsonMapper.Builder    : true
+
+written : {"@class":"com.ankurm.migration.after.S05DefaultTyping$Envelope","body":{"@class":"com.ankurm.migration.after.S05DefaultTyping$SafePayload","note":"ok"}}
+read    : SafePayload[ok]
+rogue   : rejected with InvalidTypeIdException

docs/output/after-S07DefaultsThatFlipped.txt

@@ -0,0 +1,9 @@
+FAIL_ON_TRAILING_TOKENS      : true
+FAIL_ON_UNKNOWN_PROPERTIES   : false
+ALLOW_FINAL_FIELDS_AS_MUTATORS: false
+DEFAULT_VIEW_INCLUSION       : false
+AUTO_DETECT_CREATORS exists  : false
+
+concatenated JSON  -> rejected: MismatchedInputException
+trailing garbage   -> rejected: StreamReadException
+unknown property   -> accepted: OrderDto[orderId=1]

docs/output/before-S01MapperConstruction.txt

@@ -0,0 +1,4 @@
+output          : {"id":1,"travelDate":"2026-09-15","seatPreference":"aisle"}
+after mutation  : { "id" : 1, "travelDate" : "2026-09-15", "seatPreference" : "aisle" }
+mutation stuck  : true
+set*() mutators : 40

docs/output/before-S02ExceptionHierarchy.txt

@@ -0,0 +1,3 @@
+JsonProcessingException extends IOException : true
+caught by catch (IOException) : JsonParseException
+writeValueAsString declares    : [class com.fasterxml.jackson.core.JsonProcessingException]

docs/output/before-S03CustomHandlers.txt

@@ -0,0 +1,3 @@
+serialised   : {"amount":19.99,"currency":"USD"}
+deserialised : Money[amount=20.0, currencyCode=USD]
+base classes : com.fasterxml.jackson.databind.JsonSerializer / com.fasterxml.jackson.databind.JsonDeserializer

docs/output/before-S04ModulesAndRecords.txt

@@ -0,0 +1,4 @@
+with modules    : {"id":1,"departure":"2026-09-15","seat":"12A"}
+round-trip      : TravelPlan[id=1, departure=2026-09-15, seat=Optional[12A]]
+bare mapper     : FAILS -> InvalidDefinitionException
+bare, dates only: FAILS -> InvalidDefinitionException

docs/output/before-S05DefaultTyping.txt

@@ -0,0 +1,3 @@
+enableDefaultTyping on Jackson 2.22 ObjectMapper : true
+written : {"@class":"com.ankurm.migration.before.S05DefaultTyping$Envelope","body":{"@class":"com.ankurm.migration.before.S05DefaultTyping$SafePayload","note":"ok"}}
+read    : SafePayload[ok]

docs/output/before-S07DefaultsThatFlipped.txt

@@ -0,0 +1,9 @@
+FAIL_ON_TRAILING_TOKENS      : false
+FAIL_ON_UNKNOWN_PROPERTIES   : true
+ALLOW_FINAL_FIELDS_AS_MUTATORS: true
+DEFAULT_VIEW_INCLUSION       : true
+AUTO_DETECT_CREATORS exists  : true
+
+concatenated JSON  -> accepted: OrderDto[orderId=1]
+trailing garbage   -> accepted: OrderDto[orderId=1]
+unknown property   -> rejected: UnrecognizedPropertyException

docs/output/coexistence-S06BothOnOneClasspath.txt

@@ -0,0 +1,12 @@
+jackson 2 class : com.fasterxml.jackson.databind.ObjectMapper
+jackson 3 class : tools.jackson.databind.json.JsonMapper
+
+jackson 2 output: {"booking_id":1,"travel_date":"2026-09-15"}
+jackson 3 output: {"booking_id":1,"travel_date":"2026-09-15"}
+wire-compatible : true
+
+3 reads 2's JSON: Booking[id=1, travelDate=2026-09-15]
+2 reads 3's JSON: Booking[id=1, travelDate=2026-09-15]
+
+annotation from : jackson-annotations-2.22.jar
+  <- one jackson-annotations jar, used by both majors

docs/output/coexistence-S08WireFormatEquivalence.txt

@@ -0,0 +1,14 @@
+plain record       identical
+nested list        identical
+map                identical
+java.time          identical
+Optional present   identical
+Optional empty     identical
+NON_NULL           identical
+@JsonProperty      identical
+@JsonFormat        identical
+nulls and empties  identical
+
+cases     : 10
+mismatches: 0
+Wire format is identical across both majors for these cases.