使用Jackson自定义反序列化操作（Custom Deserialization in Jackson）

Maven依赖

<dependencies><!-- yaml --><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.14.2</version><exclusions><exclusion><artifactId>jackson-annotations</artifactId><groupId>com.fasterxml.jackson.core</groupId></exclusion><exclusion><artifactId>jackson-core</artifactId><groupId>com.fasterxml.jackson.core</groupId></exclusion></exclusions></dependency><dependency><groupId>com.fasterxml.jackson.dataformat</groupId><artifactId>jackson-dataformat-yaml</artifactId><version>2.14.2</version><exclusions><exclusion><artifactId>jackson-core</artifactId><groupId>com.fasterxml.jackson.core</groupId></exclusion><exclusion><artifactId>jackson-databind</artifactId><groupId>com.fasterxml.jackson.core</groupId></exclusion><exclusion><artifactId>snakeyaml</artifactId><groupId>org.yaml</groupId></exclusion></exclusions></dependency><dependency><groupId>org.yaml</groupId><artifactId>snakeyaml</artifactId><version>2.0</version></dependency><!--Json相关--><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-core</artifactId><version>2.14.2</version></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-annotations</artifactId><version>2.15.1</version></dependency>

Standard Deserialization

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Item {public int id;public String itemName;public User owner;
}

String json = "{\n" +"    \"id\": 1,\n" +"    \"itemName\": \"theItem\",\n" +"    \"owner\": {\n" +"        \"id\": 2,\n" +"        \"name\": \"theUser\"\n" +"    }\n" +"}";Item itemWithOwner = new ObjectMapper().readValue(json, Item.class);System.out.println(itemWithOwner); // Item(id=1, itemName=theItem, owner=User(id=2, name=theUser))

Custom Deserializer on ObjectMapper

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {public int id;public String name;
}

public class ItemDeserializer extends StdDeserializer<Item> {public ItemDeserializer() {this(null);}public ItemDeserializer(Class<?> vc) {super(vc);}@Overridepublic Item deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {JsonNode jsonNode = jsonParser.getCodec().readTree(jsonParser);int id = (Integer) ((IntNode) jsonNode.get("id")).numberValue();String itemName = jsonNode.get("itemName").asText();int userId = (Integer) ((IntNode) jsonNode.get("createdBy")).numberValue();return new Item(id, itemName, new User(userId, null));}
}

String json = "{\n" +"    \"id\": 1,\n" +"    \"itemName\": \"theItem\",\n" +"    \"createdBy\": 2\n" +"}";ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Item.class, new ItemDeserializer());
mapper.registerModule(module);Item readValue = mapper.readValue(json, Item.class);
System.out.println(readValue);// Item(id=1, itemName=theItem, owner=User(id=2, name=null))

Custom Deserializer on the Class

在上文ItemDeserializer的基础上

@Data
@NoArgsConstructor
@AllArgsConstructor
@JsonDeserialize(using = ItemDeserializer.class)
public class Item {public int id;public String itemName;public User owner;
}

String json = "{\n" +"    \"id\": 1,\n" +"    \"itemName\": \"theItem\",\n" +"    \"createdBy\": 2\n" +"}";Item itemWithOwner = new ObjectMapper().readValue(json, Item.class);
System.out.println(itemWithOwner);// Item(id=1, itemName=theItem, owner=User(id=2, name=null))

Custom Deserializer for a Generic Type

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Item {public int id;public String itemName;public Wrapper<User> owner;
}

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {public int id;public String name;
}

@Data
public class Wrapper<T> {T value;public T getValue() {return value;}public void setValue(T value) {this.value = value;}
}

public class WrapperDeserializer extends JsonDeserializer<Wrapper<?>> implements ContextualDeserializer {private JavaType type;@Overridepublic JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) {this.type = property.getType().containedType(0);return this;}@Overridepublic Wrapper<?> deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException, IOException {Wrapper<?> wrapper = new Wrapper<>();wrapper.setValue(deserializationContext.readValue(jsonParser, type));return wrapper;}
}

ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Wrapper.class, new WrapperDeserializer());
mapper.registerModule(module);String json = "{\n" +"\"id\": 1,\n" +"\"itemName\": \"theItem\",\n" +"\"owner\": {\n" +"    \"id\": 2,\n" +"    \"name\": \"theUser\"\n" +"}\n" +"}";Item readValue = mapper.readValue(json, Item.class);
System.out.println(readValue);// Item(id=1, itemName=theItem, owner=Wrapper(value=User(id=2, name=theUser)))