ContextualDeserializer for mapping JSON to different types of maps with Jackson

Question

This JSON snippet should be mapped to a Java-Objects that contains a cars field of type Map and a bikes field of ty

Answer 1

Here's how I might approach it.

import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import org.codehaus.jackson.JsonNode;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.Version;
import org.codehaus.jackson.map.BeanProperty;
import org.codehaus.jackson.map.ContextualDeserializer;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.DeserializationContext;
import org.codehaus.jackson.map.JsonDeserializer;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.module.SimpleModule;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    EmptyStringAsMapDeserializer> emptyStringAsMapDeserializer = 
        new EmptyStringAsMapDeserializer>(null, new ObjectMapper());

    SimpleModule module = new SimpleModule("ThingsDeserializer", Version.unknownVersion());
    module.addDeserializer(Map.class, emptyStringAsMapDeserializer);

    ObjectMapper mapper = new ObjectMapper().withModule(module);

    Person person = mapper.readValue(new File("input.json"), Person.class);
    System.out.println(mapper.writeValueAsString(person));
  }
}

class Person
{
  public int id;
  public String name;
  public Map cars;
  public Map bikes;
}

class Car
{
  public String color;
  public String buying_date;
}

class Bike
{
  public String color;
}

class EmptyStringAsMapDeserializer
    extends JsonDeserializer>
    implements ContextualDeserializer>
{
  private Class targetType;
  private ObjectMapper mapper;

  EmptyStringAsMapDeserializer(Class targetType, ObjectMapper mapper)
  {
    this.targetType = targetType;
    this.mapper = mapper;
  }

  @Override
  public JsonDeserializer> createContextual(DeserializationConfig config, BeanProperty property)
      throws JsonMappingException
  {
    return new EmptyStringAsMapDeserializer