jackson中自定义处置序列化和反序列化

jackson中自定义处理序列化和反序列化
对于一直用gson的人来说，如果单独用jackson，真是麻烦了，但还是得小结下了：
先来看下如何自定义把某个对象序列化为json:

先是对象：

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);

    看，相当复杂,然后看有无办法简单点，其实是有的哦；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 {
    ...
}

  { "id": 1, "itemName": "theItem", [b] "owner": { "id": 2, "name": "theUser" } [/b]} 如果要输出为如下的样子，比如； { "id": 25, "itemName": "FEDUfRgS", [b]"owner": 15 [/b]}

刚开始看，看不出两者的关系。。。。。 2 楼 sootv 2014-01-16   请问下jackson可以生成这种格式不,标准json格式是{key1:value1,key2:value2}，而我只要value,如{value1,value2} 3 楼 jackyrong 2014-01-17   sootv 写道请问下jackson可以生成这种格式不,标准json格式是{key1:value1,key2:value2}，而我只要value,如{value1,value2}

可以的，参考：http://jackyrong.iteye.com/blog/1936581

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