Jackson 3 series companion code

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.

docs/part1-objectmapper.md

@@ -0,0 +1,69 @@
+# Part 1 — ObjectMapper: reading and writing
+
+Post: <https://ankurm.com/jackson-objectmapper-guide/>
+
+## B01 — writing
+
+[`B01WriteJson.java`](../src/main/java/com/ankurm/jackson3/part1objectmapper/B01WriteJson.java)
+
+String, File and pretty-printed output.
+
+```
+{"articleId":1,"title":"Jackson Deep Dive","tags":["java","json"]}
+file     : {"articleId":1,"title":"Jackson Deep Dive","tags":["java","json"]}
+pretty   :
+{
+  "articleId" : 1,
+  "title" : "Jackson Deep Dive",
+  "tags" : [ "java", "json" ]
+}
+```
+
+## B02 — reading
+
+[`B02ReadJson.java`](../src/main/java/com/ankurm/jackson3/part1objectmapper/B02ReadJson.java)
+
+String, File and InputStream. The post's `readValue(new URL(...), ...)` example is
+deliberately not reproduced — it makes a live network call, so it could not be part of
+a reproducible run. The `InputStream` form is what an HTTP client hands you in practice.
+
+```
+from String : Jackson Deep Dive
+from File   : 1
+from Stream : [java, json]
+```
+
+## B03 — generic collections
+
+[`B03GenericCollections.java`](../src/main/java/com/ankurm/jackson3/part1objectmapper/B03GenericCollections.java)
+
+`TypeReference` lives in `tools.jackson.core.type` in Jackson 3. The example also runs
+the wrong version — `readValue(json, List.class)` — to show what it actually produces.
+
+```
+size          : 2
+element class : Article
+first title   : First
+raw element   : LinkedHashMap  <- not Article
+cast fails   : ClassCastException, as expected
+map value     : Nine
+```
+
+The failure is deferred, not immediate: the call succeeds and returns a
+`List<LinkedHashMap>`. You find out at the first cast, often far from the parse site.
+
+## B04 — property ordering
+
+[`B04PropertyOrdering.java`](../src/main/java/com/ankurm/jackson3/part1objectmapper/B04PropertyOrdering.java)
+
+Beyond the post, but it explains why your first output does not look like the article's.
+
+```
+POJO    : {"listPrice":79.99,"productId":1,"productName":"Mechanical Keyboard"}
+record  : {"productId":1,"productName":"Mechanical Keyboard","listPrice":79.99}
+ordered : {"productId":1,"productName":"Mechanical Keyboard","listPrice":79.99}
+```
+
+Getter-based POJOs serialise alphabetically; records follow declaration order;
+`@JsonPropertyOrder` overrides both. Worth pinning explicitly if the JSON is
+cached, signed, or diffed against a fixture.