Jackson1TestMapKeys.java

package javatest;

import com.google.common.collect.ImmutableMap;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.annotate.JsonCreator;
import org.codehaus.jackson.annotate.JsonProperty;
import org.codehaus.jackson.map.DeserializationContext;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.KeyDeserializer;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.SerializerProvider;
import org.codehaus.jackson.map.annotate.JsonDeserialize;
import org.codehaus.jackson.map.annotate.JsonSerialize;

import java.io.IOException;
import java.util.Collections;
import java.util.Map;

public final class Jackson1TestMapKeys
{
    public static class CustomKey
    {
        private final int id;

        public CustomKey(int id) {this.id = id;}

        public int getId()
        {
            return id;
        }

        @Override
        public boolean equals(Object o)
        {
            if (o instanceof CustomKey) {
                return id == ((CustomKey) o).id;
            }
            return false;
        }

        @Override
        public int hashCode()
        {
            return id;
        }
    }

    public static class Model
    {
        private final Map<CustomKey, String> map;

        @JsonCreator
        public Model(@JsonProperty("map") @JsonDeserialize(keyUsing = CustomKeyDeserializer.class) Map<CustomKey, String> map)
        {
            this.map = ImmutableMap.copyOf(map);
        }

        @JsonProperty
        @JsonSerialize(keyUsing = CustomKeySerializer.class)
        public Map<CustomKey, String> getMap()
        {
            return map;
        }
    }

    public static void main(String[] args)
            throws Exception
    {
        Model original = new Model(Collections.singletonMap(new CustomKey(123), "test"));

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(original);
        Model deserialized = mapper.readValue(json, Model.class);

        System.out.println(json);
        System.out.println(original.getMap().equals(deserialized.getMap()));
    }

    private static class CustomKeySerializer
            extends JsonSerializer<CustomKey>
    {
        @Override
        public void serialize(CustomKey value, JsonGenerator jgen, SerializerProvider provider)
                throws IOException
        {
            jgen.writeFieldName(String.valueOf(value.getId()));
        }
    }

    private static class CustomKeyDeserializer
            extends KeyDeserializer
    {
        @Override
        public CustomKey deserializeKey(String key, DeserializationContext ctxt)
                throws IOException
        {
            return new CustomKey(Integer.valueOf(key));
        }
    }
}

Jackson2TestMapKeys.java

package javatest;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.KeyDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.google.common.collect.ImmutableMap;

import java.io.IOException;
import java.util.Collections;
import java.util.Map;

public final class Jackson2TestMapKeys
{
    public static final class CustomKey
    {
        private final int id;

        public CustomKey(int id) {this.id = id;}

        public int getId()
        {
            return id;
        }

        @Override
        public boolean equals(Object o)
        {
            if (o instanceof CustomKey) {
                return id == ((CustomKey) o).id;
            }
            return false;
        }

        @Override
        public int hashCode()
        {
            return id;
        }
    }

    public static class Model
    {
        private final Map<CustomKey, String> map;

        @JsonCreator
        public Model(@JsonProperty("map") @JsonDeserialize(keyUsing = CustomKeyDeserializer.class) Map<CustomKey, String> map)
        {
            this.map = ImmutableMap.copyOf(map);
        }

        @JsonProperty
        @JsonSerialize(keyUsing = CustomKeySerializer.class)
        public Map<CustomKey, String> getMap()
        {
            return map;
        }
    }

    public static void main(String[] args)
            throws Exception
    {
        Model original = new Model(Collections.singletonMap(new CustomKey(123), "test"));

        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(original);
        Model deserialized = mapper.readValue(json, Model.class);

        System.out.println(json);
        System.out.println(original.getMap().equals(deserialized.getMap()));
    }

    private static class CustomKeySerializer
            extends JsonSerializer<CustomKey>
    {
        @Override
        public void serialize(CustomKey value, JsonGenerator jgen, SerializerProvider provider)
                throws IOException
        {
            jgen.writeFieldName(String.valueOf(value.getId()));
        }
    }

    private static class CustomKeyDeserializer
            extends KeyDeserializer
    {
        @Override
        public CustomKey deserializeKey(String key, DeserializationContext ctxt)
                throws IOException
        {
            return new CustomKey(Integer.valueOf(key));
        }
    }
}