杰克逊在通用名单中读了json

Question

我正在使用杰克逊来阅读json消息.我试图解析的一个值是List,另一个值包含列表中数据的类型.这是我在java中创建的结构.

public class Message<T> {
   private Timestamp time;
   private RestAction action;
   private String type;
   private List<T> data;
}

通过Class.forName();我可以得到代表列表中数据的类.问题是如何阅读清单.

Answer 1

更短的东西:

mapper.readValue(jsonString, new TypeReference<List<EntryType>>() {});

Answer 2

如果你需要将传入的json映射到List,你可以这样做

String jsonString = ...; //Your incoming json string
ObjectMapper mapper = new ObjectMapper();
Class<?> clz = Class.forName(yourTypeString);
JavaType type = mapper.getTypeFactory().constructCollectionType(List.class, clz);
List <T> result = mapper.readValue(jsonString, type);

编辑

像这样的东西,完全未经测试,从未完成

public Message<T> deserialize(JsonParser jsonParser, DeserializationContext arg1)
    throws IOException, JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper();
    ObjectCodec oc = jsonParser.getCodec();
    JsonNode node = oc.readTree(jsonParser);

    JsonNode timeStamp = node.get("time");
    Timestamp time = mapper.readValue(timeStamp, Timestamp.class);
    JsonNode restAction = node.get("action");
    RestAction action = mapper.readValue(restAction, RestAction.class);
    String type = node.get("type").getTextValue();
    Class<?> clz = Class.forName(type);
    JsonNode list = node.get("data");
    JavaType listType = mapper.getTypeFactory().constructCollectionType(List.class,   clz);
    List <T> data = mapper.readValue(list, listType);

    Message<T> message = new Message<T>;
    message.setTime(time);
    message.setAction(action);
    message.setType(type);
    message.setData(data);

    return message;
}

Answer 3

自版本 2.11（2020 年 4 月）起，Jackson 有readerForListOf方法（文档）：

ObjectMapper mapper = ObjectMapper().configure(...);
ObjectReader reader = mapper.readerForListOf(MyClass.class);
List<MyClass> list = reader.readValue(...);