BAEL-6076: Resolving Jackson JsonMappingException: Can not deserialize instance of java.lang.String out of START_OBJECT token (#13495)

jackson-modules/jackson-exceptions/src/main/java/com/baeldung/exceptions/Contact.java

@@ -0,0 +1,15 @@
+package com.baeldung.exceptions;
+
+public class Contact {
+
+    private String email;
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+}

jackson-modules/jackson-exceptions/src/main/java/com/baeldung/exceptions/Person.java

@@ -0,0 +1,33 @@
+package com.baeldung.exceptions;
+
+public class Person {
+
+    private String firstName;
+    private String lastName;
+    private String contact;
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public String getContact() {
+        return contact;
+    }
+
+    public void setContact(String contact) {
+        this.contact = contact;
+    }
+
+}

jackson-modules/jackson-exceptions/src/main/java/com/baeldung/exceptions/PersonContact.java

@@ -0,0 +1,33 @@
+package com.baeldung.exceptions;
+
+public class PersonContact {
+
+    private String firstName;
+    private String lastName;
+    private Contact contact;
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public Contact getContact() {
+        return contact;
+    }
+
+    public void setContact(Contact contact) {
+        this.contact = contact;
+    }
+
+}

jackson-modules/jackson-exceptions/src/test/java/com/baeldung/exceptions/JacksonExceptionsUnitTest.java

@@ -3,17 +3,14 @@ package com.baeldung.exceptions;
 import static org.hamcrest.Matchers.containsString;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
 
 import java.io.IOException;
 import java.util.List;
 
 import org.junit.Test;
 
-import com.baeldung.exceptions.User;
-import com.baeldung.exceptions.UserWithPrivateFields;
-import com.baeldung.exceptions.UserWithRoot;
-import com.baeldung.exceptions.Zoo;
-import com.baeldung.exceptions.ZooConfigured;
 import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
 import com.fasterxml.jackson.annotation.PropertyAccessor;
 import com.fasterxml.jackson.core.JsonFactory;
@@ -82,6 +79,32 @@ public class JacksonExceptionsUnitTest {
             .readValue(json);
     }
 
+    @Test
+    public void givenJsonObject_whenDeserializingIntoString_thenException() throws IOException {
+        final String json = "{\"firstName\":\"Azhrioun\",\"lastName\":\"Abderrahim\",\"contact\":{\"email\":\"azh@email.com\"}}";
+        final ObjectMapper mapper = new ObjectMapper();
+
+        Exception exception = assertThrows(JsonMappingException.class, () -> mapper.reader()
+            .forType(Person.class)
+            .readValue(json));
+
+        assertTrue(exception.getMessage()
+            .contains("Cannot deserialize value of type `java.lang.String` from Object value (token `JsonToken.START_OBJECT`)"));
+    }
+
+    @Test
+    public void givenJsonObject_whenDeserializingIntoObject_thenDeserialize() throws IOException {
+        final String json = "{\"firstName\":\"Azhrioun\",\"lastName\":\"Abderrahim\",\"contact\":{\"email\":\"azh@email.com\"}}";
+        final ObjectMapper mapper = new ObjectMapper();
+
+        PersonContact person = mapper.reader()
+            .forType(PersonContact.class)
+            .readValue(json);
+
+        assertEquals("azh@email.com", person.getContact()
+            .getEmail());
+    }
+
     @Test
     public void givenDefaultConstructor_whenDeserializing_thenCorrect() throws IOException {
         final String json = "{\"id\":1,\"name\":\"John\"}";