custom deserialization work

jackson/src/test/java/org/baeldung/jackson/deserialization/ItemDeserializer.java

@@ -0,0 +1,30 @@
+package org.baeldung.jackson.deserialization;
+
+import java.io.IOException;
+
+import org.baeldung.jackson.dtos.Item;
+import org.baeldung.jackson.dtos.User;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.IntNode;
+
+public class ItemDeserializer extends JsonDeserializer<Item> {
+
+    /**
+     * {"id":1,"itemNr":"theItem","owner":2}
+     */
+    @Override
+    public Item deserialize(final JsonParser jp, final DeserializationContext ctxt) throws IOException, JsonProcessingException {
+        final JsonNode node = jp.getCodec().readTree(jp);
+        final int id = (Integer) ((IntNode) node.get("id")).numberValue();
+        final String itemName = node.get("itemName").asText();
+        final int userId = (Integer) ((IntNode) node.get("owner")).numberValue();
+
+        return new Item(id, itemName, new User(userId, null));
+    }
+
+}

jackson/src/test/java/org/baeldung/jackson/deserialization/ItemDeserializerOnClass.java

@@ -0,0 +1,30 @@
+package org.baeldung.jackson.deserialization;
+
+import java.io.IOException;
+
+import org.baeldung.jackson.dtos.ItemWithSerializer;
+import org.baeldung.jackson.dtos.User;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.IntNode;
+
+public class ItemDeserializerOnClass extends JsonDeserializer<ItemWithSerializer> {
+
+    /**
+     * {"id":1,"itemNr":"theItem","owner":2}
+     */
+    @Override
+    public ItemWithSerializer deserialize(final JsonParser jp, final DeserializationContext ctxt) throws IOException, JsonProcessingException {
+        final JsonNode node = jp.getCodec().readTree(jp);
+        final int id = (Integer) ((IntNode) node.get("id")).numberValue();
+        final String itemName = node.get("itemName").asText();
+        final int userId = (Integer) ((IntNode) node.get("owner")).numberValue();
+
+        return new ItemWithSerializer(id, itemName, new User(userId, null));
+    }
+
+}

jackson/src/test/java/org/baeldung/jackson/dtos/Item.java

@@ -1,13 +1,17 @@
 package org.baeldung.jackson.dtos;
 
 public class Item {
-    public final int id;
+    public int id;
-    public final String itemNr;
+    public String itemName;
-    public final User owner;
+    public User owner;
 
-    public Item(final int id, final String itemNr, final User owner) {
+    public Item() {
+        super();
+    }
+
+    public Item(final int id, final String itemName, final User owner) {
         this.id = id;
-        this.itemNr = itemNr;
+        this.itemName = itemName;
         this.owner = owner;
     }
 
@@ -17,8 +21,8 @@ public class Item {
         return id;
     }
 
-    public String getItemNr() {
+    public String getItemName() {
-        return itemNr;
+        return itemName;
     }
 
     public User getOwner() {

jackson/src/test/java/org/baeldung/jackson/dtos/ItemWithSerializer.java

@@ -1,18 +1,21 @@
 package org.baeldung.jackson.dtos;
 
+import org.baeldung.jackson.deserialization.ItemDeserializerOnClass;
 import org.baeldung.jackson.serialization.ItemSerializerOnClass;
 
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import com.fasterxml.jackson.databind.annotation.JsonSerialize;
 
 @JsonSerialize(using = ItemSerializerOnClass.class)
+@JsonDeserialize(using = ItemDeserializerOnClass.class)
 public class ItemWithSerializer {
     public final int id;
-    public final String itemNr;
+    public final String itemName;
     public final User owner;
 
-    public ItemWithSerializer(final int id, final String itemNr, final User owner) {
+    public ItemWithSerializer(final int id, final String itemName, final User owner) {
         this.id = id;
-        this.itemNr = itemNr;
+        this.itemName = itemName;
         this.owner = owner;
     }
 
@@ -22,8 +25,8 @@ public class ItemWithSerializer {
         return id;
     }
 
-    public String getItemNr() {
+    public String getItemName() {
-        return itemNr;
+        return itemName;
     }
 
     public User getOwner() {

jackson/src/test/java/org/baeldung/jackson/dtos/User.java

@@ -1,8 +1,12 @@
 package org.baeldung.jackson.dtos;
 
 public class User {
-    public final int id;
+    public int id;
-    public final String name;
+    public String name;
+
+    public User() {
+        super();
+    }
 
     public User(final int id, final String name) {
         this.id = id;

jackson/src/test/java/org/baeldung/jackson/serialization/ItemSerializer.java

@@ -15,8 +15,8 @@ public class ItemSerializer extends JsonSerializer<Item> {
     public final void serialize(final Item value, final JsonGenerator jgen, final SerializerProvider provider) throws IOException, JsonProcessingException {
         jgen.writeStartObject();
         jgen.writeNumberField("id", value.id);
-        jgen.writeStringField("itemNr", value.itemNr);
+        jgen.writeStringField("itemName", value.itemName);
-        jgen.writeNumberField("createdBy", value.owner.id);
+        jgen.writeNumberField("owner", value.owner.id);
         jgen.writeEndObject();
     }
 

jackson/src/test/java/org/baeldung/jackson/serialization/ItemSerializerOnClass.java

@@ -15,8 +15,8 @@ public class ItemSerializerOnClass extends JsonSerializer<ItemWithSerializer> {
     public final void serialize(final ItemWithSerializer value, final JsonGenerator jgen, final SerializerProvider provider) throws IOException, JsonProcessingException {
         jgen.writeStartObject();
         jgen.writeNumberField("id", value.id);
-        jgen.writeStringField("itemNr", value.itemNr);
+        jgen.writeStringField("itemName", value.itemName);
-        jgen.writeNumberField("createdBy", value.owner.id);
+        jgen.writeNumberField("owner", value.owner.id);
         jgen.writeEndObject();
     }
 

jackson/src/test/java/org/baeldung/jackson/test/JacksonDeserializationUnitTest.java

@@ -1,11 +1,15 @@
 package org.baeldung.jackson.test;
 
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.notNullValue;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThat;
 
 import java.io.IOException;
 
+import org.baeldung.jackson.deserialization.ItemDeserializer;
+import org.baeldung.jackson.dtos.Item;
+import org.baeldung.jackson.dtos.ItemWithSerializer;
 import org.baeldung.jackson.dtos.MyDto;
 import org.baeldung.jackson.dtos.ignore.MyDtoIgnoreUnknown;
 import org.junit.Test;
@@ -18,7 +22,7 @@ import com.fasterxml.jackson.databind.JsonMappingException;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException;
-
+import com.fasterxml.jackson.databind.module.SimpleModule;
 
 public class JacksonDeserializationUnitTest {
 
@@ -130,4 +134,35 @@ public class JacksonDeserializationUnitTest {
         assertThat(jsonNode1.textValue(), equalTo("v1"));
     }
 
+    // custom deserialization
+
+    @Test
+    public final void whenDeserializingTheStandardRepresentation_thenCorrect() throws JsonParseException, JsonMappingException, IOException {
+        final String json = "{\"id\":1,\"itemName\":\"theItem\",\"owner\":{\"id\":2,\"name\":\"theUser\"}}";
+
+        final Item readValue = new ObjectMapper().readValue(json, Item.class);
+        assertThat(readValue, notNullValue());
+    }
+
+    @Test
+    public final void whenDeserializingANonStandardRepresentation_thenCorrect() throws JsonParseException, JsonMappingException, IOException {
+        final String json = "{\"id\":1,\"itemName\":\"theItem\",\"owner\":2}";
+        final ObjectMapper mapper = new ObjectMapper();
+
+        final SimpleModule module = new SimpleModule();
+        module.addDeserializer(Item.class, new ItemDeserializer());
+        mapper.registerModule(module);
+
+        final Item readValue = mapper.readValue(json, Item.class);
+        assertThat(readValue, notNullValue());
+    }
+
+    @Test
+    public final void givenDeserializerIsOnClass_whenDeserializingCustomRepresentation_thenCorrect() throws JsonParseException, JsonMappingException, IOException {
+        final String json = "{\"id\":1,\"itemName\":\"theItem\",\"owner\":2}";
+
+        final ItemWithSerializer readValue = new ObjectMapper().readValue(json, ItemWithSerializer.class);
+        assertThat(readValue, notNullValue());
+    }
+
 }