Ankur
c438afc33b
37 runnable examples covering the eight feature posts on ankurm.com, verified against Jackson 3.2.1 on Temurin 21.0.5. Every output committed under docs/ was produced by run-all.sh. Also documents 11 places where the published snippets do not compile or do not behave as printed against a real Jackson 3 build - most notably that writeValueAsString(List<Base>) silently drops the polymorphic type discriminator, so the post's serialised output cannot be read back.
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Part 0 — Jackson 101: setup and the ObjectMapper lifecycle
Post: https://ankurm.com/jackson-java-tutorial/
A01 — first round-trip
A plain POJO out to JSON and back, using JsonMapper.builder().build() in place of
new ObjectMapper(). Note there is no throws clause: Jackson 3 exceptions are unchecked.
{"listPrice":79.99,"productId":1,"productName":"Mechanical Keyboard"}
Mechanical Keyboard
The property order is alphabetical, not declaration order — the post shows
productId first. That is not a Jackson 3 change; it is how getter-based POJOs have
always been introspected. Records behave differently. See
Part 1 / B04.
A02 — the shared mapper
A02SharedMapperConfiguration.java
The post's central rule — build once, share everywhere — is enforced by the API in Jackson 3 rather than left to discipline. Three of the four lines people copy from Jackson 2 configuration are unnecessary or invalid here:
| Jackson 2 line | Status in Jackson 3 |
|---|---|
.registerModule(new JavaTimeModule()) |
Delete. Built in; the class does not exist under tools.jackson. |
.registerModule(new Jdk8Module()) |
Delete. Same. |
.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS) |
Does not compile. Moved to DateTimeFeature, and already off. |
.configure(FAIL_ON_UNKNOWN_PROPERTIES, false) |
Redundant — already the default. |
.setSerializationInclusion(NON_NULL) |
Replaced by .changeDefaultPropertyInclusion(...). |
configured : {"invoiceId":500,"customerName":"Alice","issuedOn":"2026-04-09"}
defaults : {"invoiceId":500,"customerName":"Alice","issuedOn":"2026-04-09","note":null}
ObjectMapper set*() methods in Jackson 3: 0
The last line is the point: tools.jackson.databind.ObjectMapper has zero set*
methods. Reconfiguring a shared mapper is not discouraged in Jackson 3, it is impossible.
A03 — the three processing models
The same payload read by data binding, the tree model and the streaming parser.
1. data binding : Order[orderId=1001, status=SHIPPED]
2. tree model : orderId=1001 status=SHIPPED
3. streaming : orderId=1001 status=SHIPPED
For what each approach costs on a real file, see Part 6 / G04.