Add code to enable deserializing tagged union using sealed class

src/main/java/app/work/Animal.java

@@ -0,0 +1,30 @@
+package app.work;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+
+@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "type", visible = true)
+@JsonSubTypes({
+    @JsonSubTypes.Type(value = Dog.class, name = "dog"),
+    @JsonSubTypes.Type(value = Cat.class, name = "cat")
+})
+public abstract sealed class Animal {
+    @JsonProperty
+    String type;
+}
+
+final class Dog extends Animal {
+    @JsonProperty
+    String bone;
+    public Dog() {
+        this.type = "dog";
+    }
+}
+final class Cat extends Animal {
+    @JsonProperty
+    String milk;
+    public Cat() {
+        this.type = "cat";
+    }
+}

src/main/java/app/work/WorkController.java

@@ -81,6 +81,14 @@ public String hello() {
     return "bar";
   }
 
+  @PostMapping("parse")
+  public String parseADT(@RequestBody Animal animal) {
+    return switch(animal) {
+      case Dog d -> d.bone;
+      case Cat c -> c.milk;
+    };
+  }
+
   @WithSpan
   private void doSomeWork(int time) throws InterruptedException {
     log.info("doing work for " + time + "ms");

src/test/java/app/work/TestAnimal.java

@@ -0,0 +1,42 @@
+package app.work;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.junit.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class TestAnimal {
+    @Test
+    public void deserialize() throws IOException {
+        var file = new File("src/test/resources/dog.json");
+        Animal dog = new ObjectMapper().readerFor(Animal.class).readValue(file);
+
+        assertEquals("dog", dog.type);
+        assertEquals(Dog.class, dog.getClass());
+    }
+
+    @Test
+    public void testDeserializeDog() throws Exception {
+        String json = "{\"type\":\"dog\", \"bone\":\"chew toy\"}";
+
+        Animal animal = new ObjectMapper().readValue(json, Animal.class);
+        assertEquals(Dog.class, animal.getClass());
+        Dog dog = (Dog) animal;
+        assertEquals("chew toy", dog.bone);
+    }
+
+    @Test
+    public void testDeserializeCat() throws Exception {
+        String json = "{\"type\":\"cat\", \"milk\":\"almond milk\"}";
+
+        Animal animal = new ObjectMapper().readValue(json, Animal.class);
+        assertEquals(Cat.class, animal.getClass());
+        Cat cat = (Cat) animal;
+        assertEquals("almond milk", cat.milk);
+    }
+
+}

src/test/resources/dog.json

@@ -0,0 +1,4 @@
+{
+    "type": "dog",
+    "bone": "beef"
+}