CollectionSerializer gets confused on how to handle elements

[ghost]

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.fasterxml.jackson.databind.util.StdConverter;
import org.junit.Test;

public class BugTest {

    private static class Base {
        @JsonProperty
        @JsonSerialize(contentAs=Inner.Serializable.class)
        private List<Inner> innerList = new LinkedList<Inner>();
    }

    private static class Inner {
        /**
         * Work around for: https://github.com/FasterXML/jackson-databind/issues/357
         */
        @JsonSerialize(converter=InnerConverter.class)
        public static class Serializable extends Inner {}

        @JsonProperty("0")
        private String stringProperty;

        @JsonProperty("1")
        private int intProperty;
    }

    private static class InnerConverter extends StdConverter<Inner, List> {

        @Override
        @SuppressWarnings("unchecked")
        public List convert(Inner value) {
            List list = new LinkedList();

            Map map = new ObjectMapper().convertValue(value, Map.class);
            for(int i = 0; i < map.size(); i++)
                list.add(map.get(String.valueOf(i)));

            return list;
        }
    }

    @Test
    public void test() throws Exception {
        Inner inner1 = new Inner();
        inner1.stringProperty = "abc";
        inner1.intProperty = 123;

        Inner inner2 = new Inner();
        inner2.stringProperty = "def";
        inner2.intProperty = 456;

        Base base = new Base();
        base.innerList = Arrays.asList(inner1, inner2);

        assertEquals("{innerList: [[\"abc\", 123], [\"def\", 456]]}", new ObjectMapper().writeValueAsString(base));
    }
}

com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class java.lang.String and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: Base["innerList"]->java.util.ArrayList[0]->java.util.LinkedList[0])
    at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:59)
    at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:26)
    at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serializeContentsUsing(CollectionSerializer.java:145)

[ghost]

A deserialization converter works in this manner, so as a work-around, I am using a Serializer instead of a converter on the serialization side.

...
    private static class InnerSerializer extends StdSerializer<Inner> {
        protected InnerSerializer() {
            super(Inner.class);
        }

        @Override
        public void serialize(Inner value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
            jgen.writeStartArray();
            Map map = new ObjectMapper().convertValue(value, Map.class);
            for(int i = 0; i < map.size(); i++)
                jgen.writeObject(map.get(String.valueOf(i)));
            jgen.writeEndArray();
        }
    }
...

JSON: "{innerList: [["abc": 123], ["def", 456]]}"

JSON  ->  deserialization via converter  ->  POJO  ->  serialization via serializer  ->  JSON

[ghost]

Quick update. In the case anyone comes across this, I solved my root problem in a much, much simpler way by using:

@JsonFormat(shape=JsonFormat.Shape.ARRAY)
@JsonPropertyOrder({"stringProperty", "intProperty"})

I should have known there was a way to do this natively, I just didn't look hard enough.

[cowtowncoder]

@roguefrequency ah yes. This is yet another feature that is not widely known, or extensively documented. I have blogged about it a bit, but it needs to catch on so there'll be more google hits :)