Json Java Data Binding for multiple POJOs - jackson

Question

Is it possible to parse a JSON containing multiple Objects with the ObjectMapper? For example
{
"employee": {
"name": "John",
"surname": "Smith",
"age": 30,
"department": "sales"
},
"department": {
"name": "sales",
"company": "abcd",
"lead": "Mr Harrison"
},
"company": {
"name": "abcd",
"location": "New York"
}
}
Can I get the objects Employee, Department, Company out of that file in one single mapper run, something like:
ObjectMapper mapper = new ObjectMapper();
List of Objects = mapper.readValue(...)
Or is it not possible?

Answer 1

Make a parent object that contains the 3 objects you are looking for, and read them into that single object, then use that object to access your data.

Answer 2

If we consider the case of
reading numerous objects in one file separately
, without creating a dedicated wrapper POJO, this is also possible to achieve, provided that you have the information to which target object type should be mapped each of the root-level keys in the JSON.
This information can be represented in a Map:
Map<String, Class<?>> targetTypes = new HashMap<>();
targetTypes.put("employee", Employee.class);
targetTypes.put("department", Department.class);
targetTypes.put("company", Company.class);
The deserialization will have to be done in two steps. The first one is to transform the original JSON into a Map<String, Object>:
String json = ... // the JSON
ObjectMapper mapper = new ObjectMapper();
Map<String, Object> parsed = mapper.readValue(json, Map.class);
The second step is to match the keys of this map with the target types and transform the values into objects:
List<Object> objects = parsed.entrySet().stream().map(
(entry) -> {
Class<?> targetClass = targetTypes.get(entry.getKey());
return mapper.convertValue(entry.getValue(), targetClass);
}
).collect(Collectors.toList());
The objects list now contains
[
Employee(name=John, surname=Smith, age=30, department=sales),
Department(name=sales, company=abcd, lead=Mr Harrison),
Company(name=abcd, location=New York)
]