如何使用基于java.util.Map的类序列化Jackson

Question

I have a class which looks like this:

@JsonFormat(shape=JsonFormat.Shape.OBJECT)
public class MyMap implements Map<String, String>
{
    protected Map<String, String> myMap = new HashMap<String, String>();

    protected String myProperty = "my property";
    public String getMyProperty()
    {
        return myProperty;
    }
    public void setMyProperty(String myProperty)
    {
        this.myProperty = myProperty;
    }

    //
    // java.util.Map mathods implementations
    // ...
}

And a main method with this code:

            MyMap map = new MyMap();
            map.put("str1", "str2");

            ObjectMapper mapper = new ObjectMapper();
            mapper.getDeserializationConfig().withAnnotationIntrospector(new JacksonAnnotationIntrospector());
            mapper.getSerializationConfig().withAnnotationIntrospector(new JacksonAnnotationIntrospector());
            System.out.println(mapper.writeValueAsString(map));

When executing this code I'm getting the following output: {"str1":"str2"}

My question is why the internal property "myProperty" is not serialized with the map? What should be done to serialize internal properties?

Answer 1

Most probably you will end up with implementing your own serializer which will handle your custom Map type. Please refer to this question for more information.

If you choose to replace inheritance with composition, that is to make your class to include a map field not to extend a map, then it is pretty easy to solve this using the @JsonAnyGetter annotation .

Here is an example:

public class JacksonMap {

    public static class Bean {
        private final String field;
        private final Map<String, Object> map;

        public Bean(String field, Map<String, Object> map) {
            this.field = field;
            this.map = map;
        }

        public String getField() {
            return field;
        }

        @JsonAnyGetter
        public Map<String, Object> getMap() {
            return map;
        }
    }

    public static void main(String[] args) throws JsonProcessingException {
        Bean map = new Bean("value1", Collections.<String, Object>singletonMap("key1", "value2"));
        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.writeValueAsString(map));
    }
}

Output:

{"field":"value1","key1":"value2"}