Custom Jackson Deserializer to handle a property of any bean

Question

I have a class called Channel which will have roles property as follows

public class Channel{
   private int id;
   private String roles;
}

And my JSON from client would be

{
 "id":"12345787654323468",
 "roles":[
          {"name":"admin","permissions":["can publish","can reject"]},
          {"name":"moderator","permissions":["can publish","can reject"]}
         ]
}

But when I convert this JSON to Channel object I am getting following exception

com.google.appengine.repackaged.org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.lang.String out of START_ARRAY token
 at [Source: java.io.StringReader@6d25f91; line: 1, column: 253] (through reference chain: com.pokuri.entity.Channel["roles"])

Now I want to deserialize this as a string into property roles of Channel class. Also can I write single custom deserializer to handle property of JSON array in any bean.

Answer 1

A custom Deserializer can do the trick here. :

class CustomDeserializer extends JsonDeserializer<String> {

    @Override
    public String deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException, JsonProcessingException {

        JsonNode node = jsonParser.readValueAsTree();       
        return node.toString();
    }

}

now to use this in your bean, you have to include it on roles field :

class Channel {
    private long id;

    @JsonDeserialize(using = CustomDeserializer.class)
    private String roles;



    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getRoles() {
        return roles;
    }

    public void setRoles(String roles) {
        this.roles = roles;
    }

}

Note : I have taken value of id as long as it was showing error for int , as value is too large in id attribute.

Now ObjectMapper can easily deserialize your JSON to Channel class :

String json = "{\"id\":\"12345787654323468\",\"roles\":[{\"name\":\"admin\",\"permissions\":[\"can publish\",\"can reject\"]},{\"name\":\"moderator\",\"permissions\":[\"can publish\",\"can reject\"]}]}";

ObjectMapper mapper = new ObjectMapper();
Channel channel = mapper.readValue(json, Channel.class);

System.out.println("Roles :"+channel.getRoles());