将 JSON 字符串反序列化为 POJO 列表

Question

这是我用于反序列化从 Google App Engine Cloud Endpoint 返回的响应的代码：

String jsonString = IOUtils.toString(
    httpResponse.getEntity().getContent(), "UTF-8");

ObjectMapper mapper = new ObjectMapper();
ArrayList<myPOJO> myList= 
    mapper.readValue(jsonString, new TypeReference<ArrayList<MyPOJO>>(){});

jsonString 看起来像这样：

{
  "items" : [ {
    "id" : "12345",
    "name" : "test1"
  }, {
    "id" : "121212",
    "name" : "test2"
  } ]
}

但我收到此错误：

org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token at [Source: java.io.StringReader@547a7880; line: 1, column: 1]

使用 Jackson 将此 JSON 反序列化为 POJO 列表的正确方法是什么？

Answer 1

您必须为您的JSON 根对象创建根POJO。例如：

class Root {

    private List<Entity> items;

    //getters, setters, toString, etc
}

class Entity {

    private long id;
    private String name;

    //getters, setters, toString, etc
}

简单的应用：

ObjectMapper mapper = new ObjectMapper();
Root list = mapper.readValue(json, Root.class);
System.out.println(list);

打印：

Root [items=[Entity [id=12345, name=test1], Entity [id=121212, name=test2]]]

Answer 2

尝试使用映射器直接反序列化

String jsonString = IOUtils.toString(
        httpResponse.getEntity().getContent(), "UTF-8");

    ObjectMapper mapper = new ObjectMapper();

    List<MyPOJO> myList= mapper.convertValue(jsonString, mapper.getTypeFactory().constructCollectionType(List.class, MyPOJO.class));