eugenp · xaeldung · Nov 11, 2025 · Nov 11, 2025
diff --git a/json-modules/json-3/src/main/java/com/baeldung/pojomapping/Address.java b/json-modules/json-3/src/main/java/com/baeldung/pojomapping/Address.java
@@ -0,0 +1,22 @@
+package com.baeldung.pojomapping;
+
+public class Address {
+    private String city;
+    private String postalCode;
+
+    public String getCity() {
+        return city;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public String getPostalCode() {
+        return postalCode;
+    }
+
+    public void setPostalCode(String postalCode) {
+        this.postalCode = postalCode;
+    }
+}
diff --git a/json-modules/json-3/src/main/java/com/baeldung/pojomapping/Animal.java b/json-modules/json-3/src/main/java/com/baeldung/pojomapping/Animal.java
@@ -0,0 +1,49 @@
+package com.baeldung.pojomapping;
+
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+
+@JsonTypeInfo(
+    use = JsonTypeInfo.Id.NAME,
+    include = JsonTypeInfo.As.PROPERTY,
+    property = "type"
+)
+@JsonSubTypes({
+    @JsonSubTypes.Type(value = Dog.class, name = "dog"),
+    @JsonSubTypes.Type(value = Cat.class, name = "cat")
+})
+abstract class Animal {
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}
+
+class Dog extends Animal {
+    private int barkVolume;
+
+    public int getBarkVolume() {
+        return barkVolume;
+    }
+
+    public void setBarkVolume(int barkVolume) {
+        this.barkVolume = barkVolume;
+    }
+}
+
+class Cat extends Animal {
+    private boolean likesFish;
+
+    public boolean isLikesFish() {
+        return likesFish;
+    }
+
+    public void setLikesFish(boolean likesFish) {
+        this.likesFish = likesFish;
+    }
+}
diff --git a/json-modules/json-3/src/main/java/com/baeldung/pojomapping/JsonToPojoMapper.java b/json-modules/json-3/src/main/java/com/baeldung/pojomapping/JsonToPojoMapper.java
@@ -0,0 +1,37 @@
+package com.baeldung.pojomapping;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.gson.Gson;
+import org.json.JSONObject;
+
+public class JsonToPojoMapper {
+
+    public static User mapManually(JSONObject jsonObject) {
+        User user = new User();
+        user.setName(jsonObject.getString("name"));
+        user.setAge(jsonObject.getInt("age"));
+        user.setEmail(jsonObject.getString("email"));
+
+        JSONObject addressObject = jsonObject.getJSONObject("address");
+        Address address = new Address();
+        address.setCity(addressObject.getString("city"));
+        address.setPostalCode(addressObject.getString("postalCode"));
+        user.setAddress(address);
+
+        return user;
+    }
+
+    public static User mapWithJackson(JSONObject jsonObject) {
+        ObjectMapper mapper = new ObjectMapper();
+        try {
+            return mapper.readValue(jsonObject.toString(), User.class);
+        } catch (Exception e) {
+            return null;
+        }
+    }
+
+    public static User mapWithGson(JSONObject jsonObject) {
+        Gson gson = new Gson();
+        return gson.fromJson(jsonObject.toString(), User.class);
+    }
+}
diff --git a/json-modules/json-3/src/main/java/com/baeldung/pojomapping/User.java b/json-modules/json-3/src/main/java/com/baeldung/pojomapping/User.java
@@ -0,0 +1,52 @@
+package com.baeldung.pojomapping;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import java.util.List;
+
+public class User {
+    private String name;
+    private int age;
+    private String email;
+    private Address address;
+    private List<String> phones;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+
+    public List<String> getPhones() {
+        return phones;
+    }
+
+    public void setPhones(List<String> phones) {
+        this.phones = phones;
+    }
+}
diff --git a/json-modules/json-3/src/test/java/com/baeldung/pojomapping/JsonToPojoMapperUnitTest.java b/json-modules/json-3/src/test/java/com/baeldung/pojomapping/JsonToPojoMapperUnitTest.java
@@ -0,0 +1,136 @@
+package com.baeldung.pojomapping;
+
+import java.util.List;
+
+import org.json.JSONObject;
+import org.junit.jupiter.api.BeforeEach;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class JsonToPojoMapperUnitTest {
+
+    private JSONObject simpleJsonObject;
+    private JSONObject jsonObjectWithPhones;
+    private String jsonArrayString;
+
+    @BeforeEach
+    public void setUp() {
+        String simpleJsonString = """
+    {
+      "name": "Alice",
+      "age": 25,
+      "email": "alice@example.com",
+      "address": {
+        "city": "Singapore",
+        "postalCode": "123456"
+      }
+    }
+    """;
+        simpleJsonObject = new JSONObject(simpleJsonString);
+
+        String jsonStringWithPhones = """
+    {
+      "name": "Alice",
+      "age": 25,
+      "email": "alice@example.com",
+      "address": {
+        "city": "Singapore",
+        "postalCode": "123456"
+      },
+      "phones": ["12345678", "87654321"]
+    }
+    """;
+        jsonObjectWithPhones = new JSONObject(jsonStringWithPhones);
+
+        jsonArrayString = """
+    [
+      { "type": "dog", "name": "Buddy", "barkVolume": 5 },
+      { "type": "cat", "name": "Mimi", "likesFish": true }
+    ]
+    """;
+    }
+
+    @Test
+    public void givenSimpleJsonObject_whenMappedManually_thenUserPojoIsCreatedCorrectly() {
+        User user = JsonToPojoMapper.mapManually(simpleJsonObject);
+
+        assertEquals("Alice", user.getName());
+        assertEquals(25, user.getAge());
+        assertEquals("alice@example.com", user.getEmail());
+        assertEquals("Singapore", user.getAddress().getCity());
+        assertEquals("123456", user.getAddress().getPostalCode());
+    }
+
+    @Test
+    public void givenNestedJsonObject_whenMappedManually_thenAddressIsPopulatedCorrectly() {
+        User user = JsonToPojoMapper.mapManually(simpleJsonObject);
+
+        assertNotNull(user.getAddress());
+        assertEquals("Singapore", user.getAddress().getCity());
+        assertEquals("123456", user.getAddress().getPostalCode());
+    }
+
+    @Test
+    public void givenSimpleJsonObject_whenMappedWithJackson_thenUserPojoIsCreatedCorrectly() {
+        User user = JsonToPojoMapper.mapWithJackson(simpleJsonObject);
+
+        assertEquals("Alice", user.getName());
+        assertEquals("Singapore", user.getAddress().getCity());
+        assertEquals("123456", user.getAddress().getPostalCode());
+    }
+
+    @Test
+    public void givenJsonObjectWithPhones_whenMappedWithJackson_thenPhonesListIsPopulatedCorrectly() {
+        User user = JsonToPojoMapper.mapWithJackson(jsonObjectWithPhones);
+
+        assertEquals("Alice", user.getName());
+        assertEquals("Singapore", user.getAddress().getCity());
+        assertEquals("123456", user.getAddress().getPostalCode());
+        assertEquals(2, user.getPhones().size());
+        assertEquals("12345678", user.getPhones().get(0));
+        assertEquals("87654321", user.getPhones().get(1));
+    }
+
+    @Test
+    public void givenSimpleJsonObject_whenMappedWithGson_thenUserPojoIsCreatedCorrectly() {
+        User user = JsonToPojoMapper.mapWithGson(simpleJsonObject);
+
+        assertEquals("Alice", user.getName());
+        assertEquals(25, user.getAge());
+        assertEquals("Singapore", user.getAddress().getCity());
+    }
+
+    @Test
+    public void givenJsonObjectWithPhones_whenMappedWithGson_thenPhonesListIsPopulatedCorrectly() {
+        User user = JsonToPojoMapper.mapWithGson(jsonObjectWithPhones);
+
+        assertEquals("Alice", user.getName());
+        assertEquals(25, user.getAge());
+        assertEquals("Singapore", user.getAddress().getCity());
+        assertEquals(2, user.getPhones().size());
+    }
+
+    @Test
+    public void givenPolymorphicJsonArray_whenMappedWithJackson_thenCorrectSubclassesAreCreated() throws Exception {
+        ObjectMapper mapper = new ObjectMapper();
+        List<Animal> animals = Arrays.asList(
+            mapper.readValue(jsonArrayString, Animal[].class)
+        );
+
+        assertEquals(2, animals.size());
+
+        assertTrue(animals.get(0) instanceof Dog);
+        Dog dog = (Dog) animals.get(0);
+        assertEquals("Buddy", dog.getName());
+        assertEquals(5, dog.getBarkVolume());
+
+        assertTrue(animals.get(1) instanceof Cat);
+        Cat cat = (Cat) animals.get(1);
+        assertEquals("Mimi", cat.getName());
+        assertTrue(cat.isLikesFish());
+    }
+}