Jackson Json Object mapper : how to map an array? - json

Question

I am trying to map an array from a backend api call. How can I map this data knowing that :
the following classes will be used to hold the json array data :
#Data
private static class UserListBean {
private List<UserBean> userList;
}
#Data
private static class UserBean {
private String id;
private String userName;
private String password;
}
the json will have the following format (the following example just have one item in it) :
[
{
"id":1,
"userName":"bob",
"password":"403437d5c3f70b1329f37a9ecce02adbbf3e986"
}
]
I am using Jackson and I have tried the following so far but it keeps sending me back an exception
final ObjectMapper mapper = new ObjectMapper();
mapper.configure(Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
final ObjectReader reader = mapper.reader(UserListBean.class);
GeoHubAccountListBean accounts = null;
try {
accounts = reader.readValue(jsonString);
} catch (final IOException ex) {
log.error("Cannot convert JSON into a list of users", ex);
}
Here the final ObjectReader reader = mapper.reader(UserListBean.class); throws an exception
Can not deserialize instance of com.xxx.XXX$UserListBean out of START_ARRAY token
Any idea ?
thanks

Answer 1

Well, if you are trying to deserialize json to an object of type UserListBean, then you need to deserialize a JSONObject (Java Objects tend to map to JSONObjects).
Therefore, your outer most json construct should be an object. Your outer most json construct is a JSONArray.
Your UserListBean has a single field, which is a List<UserBean>. So your top level json construct (which is a JSONObject) should contain a single field with the name 'userList' with a value that is a JSONArray (Java Collections tend to map to JSONArrays).
I think this is the actual json you are looking for:
{
"userList":[
{
"id":1,
"userName":"bob",
"password":"403437d5c3f70b1329f37a9ecce02adbbf3e986"
}
]
}
If you have no control over the json coming in, then you probably want to ditch the parent object UserListBean and deal directly with the List<UserBean>, as that would work with the json you have provided.

Answer 2

Try something like the following:
public static <T> T mapFromJson(String json, Class<T> clazz) throws JsonParseException, JsonMappingException, IOException {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(new JavaTimeModule());
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
return objectMapper.readValue(json, clazz);
}
public static void main(String[] args) throws IOException {
HeaVO HeaVO=new HearVO();
HeaVO.setId("Id");
List<HeaVO> listVO=new ArrayList<HeaVO>();
listVO.add(HeaVO);
List<HeaVO> listHeaVORes=Arrays.asList(mapFromJson(mapToJson(listHeaVO), HeaVO[].class));
System.out.println(((HeaVO)listVORes.get(0)).getId());
}