Part 5: all four @JsonTypeInfo include strategies, executed

src/main/java/com/ankurm/jackson3/part5polymorphic/F03IncludeStrategies.java

@@ -0,0 +1,54 @@
+package com.ankurm.jackson3.part5polymorphic;
+
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import tools.jackson.databind.json.JsonMapper;
+
+/**
+ * Post: Polymorphic Deserialisation — https://ankurm.com/jackson-polymorphic-deserialization/
+ * Section: "@JsonTypeInfo Placement Options"
+ *
+ * The post gives a table of the four include strategies. This runs all four so you
+ * can see the actual wire format instead of trusting the table.
+ */
+public class F03IncludeStrategies {
+
+    // ---- As.PROPERTY: discriminator is an ordinary field inside the object ----
+    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "kind")
+    @JsonSubTypes(@JsonSubTypes.Type(value = PropCard.class, name = "card"))
+    public interface PropBase { }
+    public record PropCard(double amountDue) implements PropBase { }
+
+    // ---- As.WRAPPER_OBJECT: object wrapped in a single-key envelope ----
+    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.WRAPPER_OBJECT)
+    @JsonSubTypes(@JsonSubTypes.Type(value = WrapObjCard.class, name = "card"))
+    public interface WrapObjBase { }
+    public record WrapObjCard(double amountDue) implements WrapObjBase { }
+
+    // ---- As.WRAPPER_ARRAY: two-element [name, object] array ----
+    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.WRAPPER_ARRAY)
+    @JsonSubTypes(@JsonSubTypes.Type(value = WrapArrCard.class, name = "card"))
+    public interface WrapArrBase { }
+    public record WrapArrCard(double amountDue) implements WrapArrBase { }
+
+    // ---- As.EXISTING_PROPERTY: reuses a field the class already declares ----
+    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY,
+                  property = "kind", visible = true)
+    @JsonSubTypes(@JsonSubTypes.Type(value = ExistingCard.class, name = "card"))
+    public interface ExistingBase { String kind(); }
+    public record ExistingCard(String kind, double amountDue) implements ExistingBase { }
+
+    public static void main(String[] args) {
+        JsonMapper mapper = JsonMapper.builder().build();
+
+        System.out.println("PROPERTY          : " + mapper.writeValueAsString((PropBase)     new PropCard(99.0)));
+        System.out.println("WRAPPER_OBJECT    : " + mapper.writeValueAsString((WrapObjBase)  new WrapObjCard(99.0)));
+        System.out.println("WRAPPER_ARRAY     : " + mapper.writeValueAsString((WrapArrBase)  new WrapArrCard(99.0)));
+        System.out.println("EXISTING_PROPERTY : " + mapper.writeValueAsString((ExistingBase) new ExistingCard("card", 99.0)));
+
+        // Each form reads back to the correct concrete type.
+        System.out.println("read PROPERTY       -> " + mapper.readValue("{\"kind\":\"card\",\"amountDue\":99.0}", PropBase.class));
+        System.out.println("read WRAPPER_OBJECT -> " + mapper.readValue("{\"card\":{\"amountDue\":99.0}}", WrapObjBase.class));
+        System.out.println("read WRAPPER_ARRAY  -> " + mapper.readValue("[\"card\",{\"amountDue\":99.0}]", WrapArrBase.class));
+    }
+}