Serialize a Map into an array of couple using Jackson in Spring MVC

Question

First of all, I know what I am trying to do can be done using a custom JsonSerializer, but I'd like to know whether there is a less boilerplate code solution for this.

In Spring MVC, I'd like to serialize a Map into a list of couples. Let's say I'd like to return such a Map:

Map<String, String> res = new HashMap<>();
res.put("key1", "value1");
res.put("key2", "value2");

The default serialization result will give a JSON like this:

{key1: value1, key2: value2}

Is there a way to have instead something like this, without using a custom JsonSerializer?

[{key: "key1", value: "value1"}, {key: "key2", value: "value2"}]

I'm using Spring-Boot 1.3 with default versions of Spring MVC and Jackson.

Answer 1

As I prefered a reusable solution, and could not find a standard solution, I implemented it with a custom JsonSerializer, as follows:

public class MapToCoupleArraySerializer extends JsonSerializer<Map<?, ?>>{

    @Override
    public void serialize(Map<?, ?> value, JsonGenerator generator,
            SerializerProvider serializers) throws IOException,
            JsonProcessingException {
        generator.writeStartArray();
        for (Entry<?, ?> entry : value.entrySet()){
            generator.writeStartObject();
            generator.writeObjectField("key", entry.getKey());
            generator.writeObjectField("value", entry.getValue());
            generator.writeEndObject();
        }       
        generator.writeEndArray();
    }    
}

and use it in the traditionnal Spring way:

public class MyClassToSerialize{

    @JsonSerialize(using = MapToCoupleArraySerializer .class)
    private Map<Key, Value> recipes;

    // ...
}

Answer 2

try to serialize entries instead of the map itself :

Map.Entry[] entries = myMap.entrySet().toArray(new Map.Entry[]{});

I didn't try it, but the result should be similar enough to what you want.