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    <p>Here's how I might approach it.</p> <pre><code>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&lt;Map&lt;String, ?&gt;&gt; emptyStringAsMapDeserializer = new EmptyStringAsMapDeserializer&lt;Map&lt;String, ?&gt;&gt;(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&lt;String, Car&gt; cars; public Map&lt;String, Bike&gt; bikes; } class Car { public String color; public String buying_date; } class Bike { public String color; } class EmptyStringAsMapDeserializer&lt;T&gt; extends JsonDeserializer&lt;Map&lt;String, ?&gt;&gt; implements ContextualDeserializer&lt;Map&lt;String, ?&gt;&gt; { private Class&lt;?&gt; targetType; private ObjectMapper mapper; EmptyStringAsMapDeserializer(Class&lt;?&gt; targetType, ObjectMapper mapper) { this.targetType = targetType; this.mapper = mapper; } @Override public JsonDeserializer&lt;Map&lt;String, ?&gt;&gt; createContextual(DeserializationConfig config, BeanProperty property) throws JsonMappingException { return new EmptyStringAsMapDeserializer&lt;Object&gt;(property.getType().containedType(1).getRawClass(), mapper); } @Override public Map&lt;String, ?&gt; deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException { JsonNode node = jp.readValueAsTree(); if ("".equals(node.getTextValue())) return new HashMap&lt;String, Object&gt;(); ObjectMapper mapper = new ObjectMapper(); return mapper.readValue(node, mapper.getTypeFactory().constructMapType(Map.class, String.class, targetType)); } } </code></pre> <p>The generic type parameters might be a little out of order. I did a bit of quick copy-pasting.</p>
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    1. COHow could I use such a deserializer with annotations? `@JsonDeserializer(?) public void setBikes(List<Bike> bikes)`
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    2. COI recommend posting a new question.
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    3. COSorry, I've added my questions separately: http://stackoverflow.com/questions/12933394/jackson-deserialize-as-an-empty-list/12944947#12944947, http://stackoverflow.com/questions/12937197/how-to-define-a-generic-list-deserializer-through-annotations-with-jackson
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