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

Myth丶恋晨 2024-03-23 17:49 81阅读 0赞

#### 目录 ####

*  Maven依赖
 *  Standard Deserialization
 *  Custom Deserializer on ObjectMapper
 *  Custom Deserializer on the Class
 *  Custom Deserializer for a Generic Type

--------------------

## Maven依赖 ##

<dependencies>
        
        <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>
        
        <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); 
    
    结果
    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);
        }
    
        @Override
        public 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);
    
    结果
    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;
    
        @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, 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)))

\-----------------------------------------------------------------------------读书笔记摘自 文章：  
**[Getting Started with Custom Deserialization in Jackson][]**

[Getting Started with Custom Deserialization in Jackson]: https://www.baeldung.com/jackson-deserialization