BAEL-5115 Deduction-Based Polymorphism in Jackson 2.12 (#11732)

* BAEL-5115 Deduction-Based Polymorphism in Jackson 2.12

* Fix pmd

* Code review changes

* Improvements

* Code review

* Code review

* fix typo

* Rename package

* Apply formatter

* Add old deduction

* revert

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/deductionbasedpolymorphism/Character.java

@@ -0,0 +1,12 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonSubTypes.Type;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import com.fasterxml.jackson.annotation.JsonTypeInfo.Id;
+
+@JsonTypeInfo(use = Id.DEDUCTION)
+@JsonSubTypes({ @Type(ImperialSpy.class), @Type(King.class), @Type(Knight.class) })
+public interface Character {
+
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/deductionbasedpolymorphism/ControlledCharacter.java

@@ -0,0 +1,14 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+public class ControlledCharacter {
+
+    private Character character;
+
+    public Character getCharacter() {
+        return character;
+    }
+
+    public void setCharacter(Character character) {
+        this.character = character;
+    }
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/deductionbasedpolymorphism/ImperialSpy.java

@@ -0,0 +1,5 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+public class ImperialSpy implements Character {
+
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/deductionbasedpolymorphism/King.java

@@ -0,0 +1,14 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+public class King extends NamedCharacter {
+
+    private String land;
+
+    public String getLand() {
+        return land;
+    }
+
+    public void setLand(String land) {
+        this.land = land;
+    }
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/deductionbasedpolymorphism/Knight.java

@@ -0,0 +1,14 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+public class Knight extends NamedCharacter {
+
+    private String weapon;
+
+    public String getWeapon() {
+        return weapon;
+    }
+
+    public void setWeapon(String weapon) {
+        this.weapon = weapon;
+    }
+}

jackson-modules/jackson-annotations/src/main/java/com/baeldung/jackson/deductionbasedpolymorphism/NamedCharacter.java

@@ -0,0 +1,14 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+public class NamedCharacter implements Character {
+
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}

jackson-modules/jackson-annotations/src/test/java/com/baeldung/jackson/deductionbasedpolymorphism/CaseInsensitiveInferenceUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+import static com.baeldung.jackson.deductionbasedpolymorphism.JsonStringFormatterUtil.formatJson;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.MapperFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+
+class CaseInsensitiveInferenceUnitTest {
+
+    private final ObjectMapper objectMapper = JsonMapper.builder()
+        .configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true)
+        .build();
+
+    @Test
+    void givenACaseInsensitiveKnight_whenMapping_thenExpectKnight() throws Exception {
+        String knightJson = formatJson("{'NaMe':'Ostrava, of Boletaria', 'WeaPON':'Rune Sword'}");
+
+        Character character = objectMapper.readValue(knightJson, Character.class);
+
+        assertTrue(character instanceof Knight);
+        assertSame(character.getClass(), Knight.class);
+        Knight knight = (Knight) character;
+        assertEquals("Ostrava, of Boletaria", knight.getName());
+        assertEquals("Rune Sword", knight.getWeapon());
+    }
+
+}

jackson-modules/jackson-annotations/src/test/java/com/baeldung/jackson/deductionbasedpolymorphism/ContainedInferenceUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+import static com.baeldung.jackson.deductionbasedpolymorphism.JsonStringFormatterUtil.formatJson;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+
+class ContainedInferenceUnitTest {
+
+    private final ObjectMapper objectMapper = JsonMapper.builder()
+        .build();
+
+    @Test
+    void givenAKnightControlledCharacter_whenMapping_thenExpectAControlledCharacterWithKnight() throws Exception {
+        String controlledCharacterJson = formatJson("{'character': {'name': 'Ostrava, of Boletaria', 'weapon': 'Rune Sword'}}");
+
+        ControlledCharacter controlledCharacter = objectMapper.readValue(controlledCharacterJson, ControlledCharacter.class);
+        Character character = controlledCharacter.getCharacter();
+
+        assertTrue(character instanceof Knight);
+        assertSame(character.getClass(), Knight.class);
+        Knight knight = (Knight) character;
+        assertEquals("Ostrava, of Boletaria", knight.getName());
+        assertEquals("Rune Sword", knight.getWeapon());
+    }
+
+    @Test
+    void givenAKingControlledCharacter_whenMapping_thenExpectAControlledCharacterWithKing() throws Exception {
+        String controlledCharacterJson = formatJson("{'character': {'name': 'King Allant', 'land': 'Boletaria'}}");
+
+        ControlledCharacter controlledCharacter = objectMapper.readValue(controlledCharacterJson, ControlledCharacter.class);
+        Character character = controlledCharacter.getCharacter();
+
+        assertTrue(character instanceof King);
+        assertSame(character.getClass(), King.class);
+        King king = (King) character;
+        assertEquals("King Allant", king.getName());
+        assertEquals("Boletaria", king.getLand());
+    }
+
+    @Test
+    void givenAnEmptySubtype_whenMapping_thenExpectImperialSpy() throws Exception {
+        String controlledCharacterJson = formatJson("{'character': {}}");
+
+        ControlledCharacter controlledCharacter = objectMapper.readValue(controlledCharacterJson, ControlledCharacter.class);
+
+        assertTrue(controlledCharacter.getCharacter() instanceof ImperialSpy);
+    }
+
+    @Test
+    void givenANullCharacter_whenMapping_thenExpectNullCharacter() throws Exception {
+        String controlledCharacterJson = formatJson("{'character': null}");
+
+        ControlledCharacter controlledCharacter = objectMapper.readValue(controlledCharacterJson, ControlledCharacter.class);
+
+        assertNull(controlledCharacter.getCharacter());
+    }
+
+    @Test
+    void givenAAnAbsentCharacter_whenMapping_thenExpectNullCharacter() throws Exception {
+        String controlledCharacterJson = formatJson("{}");
+
+        ControlledCharacter controlledCharacter = objectMapper.readValue(controlledCharacterJson, ControlledCharacter.class);
+
+        assertNull(controlledCharacter.getCharacter());
+    }
+}

jackson-modules/jackson-annotations/src/test/java/com/baeldung/jackson/deductionbasedpolymorphism/JsonStringFormatterUtil.java

@@ -0,0 +1,9 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+public class JsonStringFormatterUtil {
+
+    public static String formatJson(String input) {
+        return input.replaceAll("'", "\"");
+    }
+
+}

jackson-modules/jackson-annotations/src/test/java/com/baeldung/jackson/deductionbasedpolymorphism/SimpleInferenceUnitTest.java

@@ -0,0 +1,61 @@
+package com.baeldung.jackson.deductionbasedpolymorphism;
+
+import static com.baeldung.jackson.deductionbasedpolymorphism.JsonStringFormatterUtil.formatJson;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+
+class SimpleInferenceUnitTest {
+
+    private final ObjectMapper objectMapper = JsonMapper.builder()
+        .build();
+
+    @Test
+    void givenAKnight_whenMapping_thenExpectAKnightType() throws Exception {
+        String knightJson = formatJson("{'name':'Ostrava, of Boletaria', 'weapon':'Rune Sword'}");
+
+        Character character = objectMapper.readValue(knightJson, Character.class);
+
+        assertTrue(character instanceof Knight);
+        assertSame(character.getClass(), Knight.class);
+        Knight king = (Knight) character;
+        assertEquals("Ostrava, of Boletaria", king.getName());
+        assertEquals("Rune Sword", king.getWeapon());
+    }
+
+    @Test
+    void givenAKing_whenMapping_thenExpectAKingType() throws Exception {
+        String kingJson = formatJson("{'name':'Old King Allant', 'land':'Boletaria'}");
+
+        Character character = objectMapper.readValue(kingJson, Character.class);
+
+        assertTrue(character instanceof King);
+        assertSame(character.getClass(), King.class);
+        King king = (King) character;
+        assertEquals("Old King Allant", king.getName());
+        assertEquals("Boletaria", king.getLand());
+    }
+
+    @Test
+    void givenAnEmptyObject_whenMapping_thenExpectAnImperialSpy() throws Exception {
+        String imperialSpyJson = "{}";
+
+        Character character = objectMapper.readValue(imperialSpyJson, Character.class);
+
+        assertTrue(character instanceof ImperialSpy);
+    }
+
+    @Test
+    void givenANullObject_whenMapping_thenExpectANullObject() throws Exception {
+        Character character = objectMapper.readValue("null", Character.class);
+
+        assertNull(character);
+    }
+
+}