JSON 和 BSON 哪个更轻量级

I have written code to serialize objects to JSON and BSON. According to my output, the BSON produced is greater in size than the JSON. Is this expected?

From my code for Bson.class (using Jackson and bson4jackson)

private ByteArrayOutputStream baos = new ByteArrayOutputStream();
private BsonFactory fac = new BsonFactory();

private ObjectMapper mapper = new ObjectMapper(fac);

public Bson(Object obj) throws JsonGenerationException,
        JsonMappingException, IOException {
    mapper.writeValue(baos, obj);
}

public int size() {
    return baos.size();
}

public String toString() {
    byte[] bytes = baos.toByteArray();
    return new String(bytes);
}

From my Json.class

private ByteArrayOutputStream baos = new ByteArrayOutputStream();
private ObjectMapper mapper = new ObjectMapper();

public Json(Object obj) throws JsonGenerationException,
        JsonMappingException, IOException {
    mapper.writeValue(baos, obj);
}

(size() and toString() as above)

My POJOs are Person.class and Address.class.

In my main class:

    Address a = new Address("Jln Koli", "90121", "Vila", "Belgium");
    Person p = new Person("Ali Bin Baba", new Date(), 90.0, 12, a);

    List<Person> persons = new LinkedList<>();
    persons.add(p);
    persons.add(p);

    Bson bson = new Bson(persons);
    Json json = new Json(persons);
    System.out.println("Bson : " + bson.size() + ", data : " + bson.toString());
    System.out.println("Json : " + json.size() + ", data : " + json.toString());

The ouput:

Bson : 301, data : -
Json : 285, data : [{"name":"Ali Bin Baba","birthd...

My Question:

1. 这个输出是真的，还是我的代码错了？
2. 有没有判断/测试、比较BSON和JSON大小的建议？