jackson自定义序列化和反序列化

原文链接:https://blog.csdn.net/liuxiao723846/article/details/42921333

new way reference
https://blog.csdn.net/z69183787/article/details/79317443
public class User { 
    public int id; 
    public String name; 
} 
public class Item { 
    public int id; 
    public String itemName; 
    public User owner; 
} 


JACKSON一般的使用很容易,如;
Item myItem = new Item(1, "theItem", new User(2, "theUser"));
String serialized = new ObjectMapper().writeValueAsString(myItem);
  结果为：
{
    "id": 1,
    "itemName": "theItem",
    "owner": {
        "id": 2,
        "name": "theUser"
    }
}

如果要输出为如下的样子，比如；
{
    "id": 25,
    "itemName": "FEDUfRgS",
    "owner": 15
}

则要自定义了，要继承JsonSerializer类，如下：
public class ItemSerializer extends JsonSerializer<Item> { 
    @Override 
    public void serialize(Item value, JsonGenerator jgen, SerializerProvider provider)  
      throws IOException, JsonProcessingException { 
        jgen.writeStartObject(); 
        jgen.writeNumberField("id", value.id); 
        jgen.writeStringField("itemName", value.itemName); 
        jgen.writeNumberField("owner", value.owner.id); 
        jgen.writeEndObject(); 
    } 
} 

然后
Item myItem = new Item(1, "theItem", new User(2, "theUser")); 
ObjectMapper mapper = new ObjectMapper(); 
  
SimpleModule module = new SimpleModule(); 
module.addSerializer(Item.class, new ItemSerializer()); 
mapper.registerModule(module); 
  
String serialized = mapper.writeValueAsString(myItem); 

简单点的方法为：
@JsonSerialize(using = ItemSerializer.class) 
public class Item { 
    ... 
} 


就是使用注解@JsonSerialize，然后：
 
Item myItem = new Item(1, "theItem", new User(2, "theUser")); 
String serialized = new ObjectMapper().writeValueAsString(myItem); 


接下来看如何反序列化了，
同样，要反序列化的两个pojo为：

 
public class User { 
    public int id; 
    public String name; 
} 
public class Item { 
    public int id; 
    public String itemName; 
    public User owner; 
} 

反序列化代码为：
Item itemWithOwner = new ObjectMapper().readValue(json, Item.class);
 
如果要自定义反序列化，比如要反序列化的JSON为;
{
    "id": 1,
    "itemName": "theItem",
    "owner": 2
}

则上面这样会报错：
com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException:
Unrecognized field "createdBy" (class org.baeldung.jackson.dtos.Item),
not marked as ignorable (3 known properties: "id", "owner", "itemName"])
at [Source: java.io.StringReader@53c7a917; line: 1, column: 43]
(through reference chain: org.baeldung.jackson.dtos.Item["createdBy"])
 
代码：
 
 
public class ItemDeserializer extends JsonDeserializer<Item> { 
  
    @Override 
    public Item deserialize(JsonParser jp, DeserializationContext ctxt)  
      throws IOException, JsonProcessingException { 
        JsonNode node = jp.getCodec().readTree(jp); 
        int id = (Integer) ((IntNode) node.get("id")).numberValue(); 
        String itemName = node.get("itemName").asText(); 
        int userId = (Integer) ((IntNode) node.get("id")).numberValue(); 
  
        return new Item(id, itemName, new User(userId, null)); 
    } 
} 
 
ObjectMapper mapper = new ObjectMapper(); 
SimpleModule module = new SimpleModule(); 
module.addDeserializer(Item.class, new ItemDeserializer()); 
mapper.registerModule(module); 
  
Item readValue = mapper.readValue(json, Item.class); 

也可以用注解：
@JsonDeserialize(using = ItemDeserializer.class)
public class Item {
    ...
}