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.

src/main/java/com/ankurm/jackson3/part0setup/A03ThreeProcessingModels.java

@@ -0,0 +1,45 @@
+package com.ankurm.jackson3.part0setup;
+
+import tools.jackson.core.JsonParser;
+import tools.jackson.core.JsonToken;
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.json.JsonMapper;
+
+/**
+ * Post: Jackson 101 — https://ankurm.com/jackson-java-tutorial/
+ * Section: "Jackson's Three Processing Models"
+ *
+ * The same payload read three ways, so the trade-off is concrete rather than a table.
+ */
+public class A03ThreeProcessingModels {
+
+    public record Order(Long orderId, String status) { }
+
+    private static final String JSON = "{\"orderId\":1001,\"status\":\"SHIPPED\"}";
+
+    public static void main(String[] args) {
+        JsonMapper mapper = JsonMapper.builder().build();
+
+        // 1. DATA BINDING — the right answer roughly 95% of the time.
+        Order bound = mapper.readValue(JSON, Order.class);
+        System.out.println("1. data binding : " + bound);
+
+        // 2. TREE MODEL — schema not known at compile time; navigate a JsonNode.
+        JsonNode tree = mapper.readTree(JSON);
+        System.out.println("2. tree model   : orderId=" + tree.path("orderId").asInt()
+                + " status=" + tree.path("status").asString());
+
+        // 3. STREAMING — token by token, constant memory, no document ever built.
+        StringBuilder streamed = new StringBuilder();
+        try (JsonParser parser = mapper.createParser(JSON)) {
+            while (parser.nextToken() != null) {
+                if (parser.currentToken() == JsonToken.PROPERTY_NAME) {
+                    String field = parser.currentName();
+                    parser.nextToken();                       // advance to the value
+                    streamed.append(field).append('=').append(parser.getString()).append(' ');
+                }
+            }
+        }
+        System.out.println("3. streaming    : " + streamed.toString().trim());
+    }
+}