Android上的MongoDB - 套接字超时

Question

我想将我的Android应用程序连接到远程MongoDB数据库：

try {
            String str = "";
            MongoClientURI uri = new MongoClientURI("mongodb://byulent:mypass@ds231549.mlab.com:31549/mydb");
            MongoClient mongoClient = new MongoClient(uri);
            MongoDatabase db = mongoClient.getDatabase(uri.getDatabase());
            MongoCollection<Document> photos = db.getCollection("photos");
            FindIterable<Document> cursor = photos.find();
            Iterator i = cursor.iterator();
            while (i.hasNext()){
                Log.d("obj", i.next().toString());
            }
            //Toast.makeText(context, "Succesfully connected to MongoDB", Toast.LENGTH_SHORT).show();
        } catch (Exception e) {
            Log.e("mongodb", e.getMessage());
        }

但是当我尝试从DB获取数据时，我看到了这个错误：

E/mongodb: Timed out after 30000 ms while waiting to connect. Client view of cluster state 
is {type=UNKNOWN, servers=[{address=ds231549.mlab.com:31549, type=UNKNOWN, state=CONNECTING,
exception={com.mongodb.MongoSocketOpenException: Exception opening socket}, caused by 
{java.net.SocketTimeoutException: failed to connect to ds231549.mlab.com/34.245.70.193 
(port 31549) after 20000ms}}]

为什么会出现此错误以及如何解决？