为分层JSON映射中的特定属性编写Jackson定制反序列化器

Question

JSON Object:

 ["emp" : { "departments": [ "modules": [ { "tasks": [ { "resources": 100, "notes": "" } ] } ] ] }] 

I would want to map the above JSON onto a List<Emp> object. My object mapper would look like:
List<Emp> emps = Arrays.asList(mapper.readValue(jsonString, Emp[].class));

This simple object mapper works well.
My problem is I have to deserialize tasks object from the JSON on to the Task object in a different manner.

I understand that we can write a custom deserializer using jackson, but that is not solving my case. I have written a CustomeDeserializer for the Task object, but registering this to the Object Mapper as follows would try to serialize the whole JSON ( List<Emp> ) as aa task object.

 SimpleModule mod = new SimpleModule("MyModule"); ObjectMapper mapper = new ObjectMapper(); mod.addDeserializer(Task.class, new CustomDeserializer(Task.class)); mapper.registerModule(mod); 

Is there a way to specify the CustomDeserializer only for a particular attribute during parsing? Or is there an alternative for this ?

Note: I cannot change my DTO's to fix this.

Answer 1

There are several alternatives for parsing JSON with Jackson. You can use Jacksons Tree model parsing or the streaming API . Both require more code than just mapper.readValue(jsonString, Emp[].class) but it's a lot better than implementing your own JSON parsing. You can read about them in the Jackson documentation here