Json deserialization into other class hierarchy using Jackson

Question

Now i'm working with Jackson and i have some questions about it.

First of all. I have two services, first is data collecting and sending service and second receive this data and, for example, log it into a file.

So, first service has class hierarchy like this:

         +----ConcreteC          | Base ----+----ConcreteA          |          +----ConcreteB 

And second service has class hierarchy like this:

ConcreteAAdapter extends ConcreteA implements Adapter {} ConcreteBAdapter extends ConcreteB implements Adapter {} ConcreteCAdapter extends ConcreteC implements Adapter {} 

The first service knows nothing about ConcreteXAdapter.

The way i'm sending the data on the first service:

Collection<Base> data = new LinkedBlockingQueue<Base>() JacksonUtils utils = new JacksonUtils(); data.add(new ConcreteA()); data.add(new ConcreteB()); data.add(new ConcreteC()); ... send(utils.marshall(data)); ...  public class JacksonUtils {      public byte[] marshall(Collection<Base> data) throws IOException {         ByteArrayOutputStream out = new ByteArrayOutputStream() {             @Override             public byte[] toByteArray() {                 return buf;             }         };          getObjectMapper().writeValue(out, data);         return out.toByteArray();     }     protected ObjectMapper getObjectMapper() {         return new ObjectMapper();     }      public Object unmarshall(byte[] json) throws IOException {         return getObjectMapper().readValue(json, Object.class);     }      public <T> T unmarshall(InputStream source, TypeReference<T> typeReference) throws IOException {         return getObjectMapper().readValue(source, typeReference);     }      public <T> T unmarshall(byte[] json, TypeReference<T> typeReference) throws IOException {         return getObjectMapper().readValue(json, typeReference);     } } 

So, i want to desirialize json into Collection of ConcreteXAdapter, not into Collection of ConcreteX (ConcreteA -> ConcreteAAdapter, ConcreteB -> ConcreteBAdapter, ConcreteC -> ConcreteCAdapter). In the case i described i want to get:

Collection [ConcreteAAdapter, ConcreteBAdapter, ConcreteCAdapter] 

How can i do this?

Answer 1

For this purpose you need to pass additional info in JSON:

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME,        include=JsonTypeInfo.As.PROPERTY, property="@type") class Base { ... } 

Then on serialization it will add @type field:

objectMapper.registerSubtypes(             new NamedType(ConcreteAAdapter.class, "ConcreteA"),             new NamedType(ConcreteBAdapter.class, "ConcreteB"),             new NamedType(ConcreteCAdapter.class, "ConcreteC")             );  // note, that for lists you need to pass TypeReference explicitly objectMapper.writerWithType(new TypeReference<List<Base>>() {})      .writeValueAsString(someList);       {       "@type" : "ConcreteA",       ...     } 

on deserialization it will be:

    objectMapper.registerSubtypes(             new NamedType(ConcreteA.class, "ConcreteA"),             new NamedType(ConcreteB.class, "ConcreteB"),             new NamedType(ConcreteC.class, "ConcreteC")             );     objectMapper.readValue(....) 

More info here