public static void main(String... args) throws UnknownHostException {
    Mongo m = new Mongo();
    m.setWriteConcern(WriteConcern.SAFE);
    DB db = m.getDB("test");
    db.dropDatabase();
    DBCollection collection = db.getCollection("tmp");
    //random docs insert
    for (int i = 0; i < 10; i++) {
        DBObject object = new BasicDBObject("_id", i);
        object.put("length", (int) (Math.random() * 100));
        collection.insert(object);
    }

    print(collection.find().toArray());
    //valid value
    BasicDBObject obj = new BasicDBObject().append("length", 1);
    print(collection.find().sort(obj).toArray());
    //string value
    obj.put("length", "randomString");
    print(collection.find().sort(obj).toArray());
    //object value
    obj.put("length", new BasicDBObject());
    print(collection.find().sort(obj).toArray());
}

private static void print(List<DBObject> list){
    System.out.println("--size "+list.size());
    for(DBObject o : list){
        System.out.println(o);
    }
    System.out.println("\n");
}