BAEL-5849 Code for the improvement of the article Custom deserializer for a generic type jackson

jackson-modules/jackson-custom-conversions/src/main/java/com/baeldung/deserialization/ItemWithWrappedUser.java

@@ -0,0 +1,31 @@
+package com.baeldung.deserialization;
+
+public class ItemWithWrappedUser {
+
+    public int id;
+    public String itemName;
+    public Wrapper<User> owner;
+
+    public ItemWithWrappedUser() {
+        super();
+    }
+
+    public ItemWithWrappedUser(final int id, final String itemName, final Wrapper<User> owner) {
+        this.id = id;
+        this.itemName = itemName;
+        this.owner = owner;
+    }
+    
+    public int getId() {
+        return id;
+    }
+
+    public String getItemName() {
+        return itemName;
+    }
+
+    public Wrapper<User> getOwner() {
+        return owner;
+    }
+
+}

jackson-modules/jackson-custom-conversions/src/main/java/com/baeldung/deserialization/Wrapper.java

@@ -0,0 +1,15 @@
+package com.baeldung.deserialization;
+
+public class Wrapper<T> {
+
+    T value;
+
+    public T getValue() {
+        return value;
+    }
+
+    public void setValue(T value) {
+        this.value = value;
+    }
+
+}

jackson-modules/jackson-custom-conversions/src/main/java/com/baeldung/deserialization/WrapperDeserializer.java

@@ -0,0 +1,30 @@
+package com.baeldung.deserialization;
+
+import java.io.IOException;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.databind.BeanProperty;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JavaType;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.deser.ContextualDeserializer;
+
+public class WrapperDeserializer extends JsonDeserializer<Wrapper<?>> implements ContextualDeserializer {
+
+    private JavaType type;
+
+    @Override
+    public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) {
+        this.type = property.getType()
+            .containedType(0);
+        return this;
+    }
+
+    @Override
+    public Wrapper<?> deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
+        Wrapper<?> wrapper = new Wrapper<>();
+        wrapper.setValue(deserializationContext.readValue(jsonParser, type));
+        return wrapper;
+    }
+
+}

jackson-modules/jackson-custom-conversions/src/test/java/com/baeldung/deserialization/CustomDeserializationUnitTest.java

@@ -1,23 +1,24 @@
 package com.baeldung.deserialization;
 
-import com.fasterxml.jackson.core.JsonParseException;
+import static org.hamcrest.CoreMatchers.is;
-import com.fasterxml.jackson.databind.DeserializationFeature;
+import static org.hamcrest.CoreMatchers.not;
-import com.fasterxml.jackson.databind.JsonMappingException;
+import static org.hamcrest.Matchers.notNullValue;
-import com.fasterxml.jackson.databind.ObjectMapper;
+import static org.junit.Assert.assertEquals;
-import com.fasterxml.jackson.databind.SerializationFeature;
+import static org.junit.Assert.assertThat;
-import com.fasterxml.jackson.databind.module.SimpleModule;
-import org.junit.Test;
 
 import java.io.IOException;
 import java.time.ZoneId;
 import java.time.ZonedDateTime;
 
-import static org.hamcrest.CoreMatchers.is;
+import org.junit.Test;
-import static org.hamcrest.CoreMatchers.not;
+
-import static org.hamcrest.Matchers.equalTo;
+import com.fasterxml.jackson.core.JsonParseException;
-import static org.hamcrest.Matchers.notNullValue;
+import com.fasterxml.jackson.core.JsonProcessingException;
-import static org.junit.Assert.assertNotNull;
+import com.fasterxml.jackson.databind.DeserializationFeature;
-import static org.junit.Assert.assertThat;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.databind.module.SimpleModule;
 
 public class CustomDeserializationUnitTest {
 
@@ -78,4 +79,23 @@ public class CustomDeserializationUnitTest {
         assertThat(restored, is(now));
     }
 
+    @Test
+    public void whenDeserialisingItemWithWrappedUser_ThenWrappedUserIsCorrectlyParsed() throws JsonProcessingException {
+        final String json = "{\"id\":1,\"itemName\":\"theItem\",\"owner\":{\"id\":2,\"name\":\"theUser\"}}";
+
+        SimpleModule module = new SimpleModule().addDeserializer(Wrapper.class, new WrapperDeserializer());
+
+        ObjectMapper objectMapper = new ObjectMapper();
+        objectMapper.registerModule(module);
+
+        final ItemWithWrappedUser readValue = objectMapper.readValue(json, ItemWithWrappedUser.class);
+
+        assertEquals(2, readValue.getOwner()
+            .getValue()
+            .getId());
+        assertEquals("theUser", readValue.getOwner()
+            .getValue()
+            .getName());
+    }
+
 }