Question

Currently I am using mongodb with java. I don’t want to reopen my connection to the datastore every time, so I thought I should make a static variable:

package Config;

import java.net.UnknownHostException;

import com.google.code.morphia.*;

import com.mongodb.Mongo;
import com.mongodb.MongoException;

public class Config {

    static String dbUrl = "url";
    static int dbPort = portnumber;
    static String username = "user";
    static String password = "pw";
    static String dbName = "dbname";
    public static Datastore ds;

    public static Datastore getDatastore() throws UnknownHostException,
            MongoException {
        if (ds == null) {
            ds = connect();
        }
        return ds;
    }

    public static Datastore connect() throws UnknownHostException,
            MongoException {
        Mongo m = new Mongo(dbUrl, dbPort);
        Datastore ds = new Morphia().createDatastore(m, dbName);
        boolean con = ds.getDB().authenticate(username, password.toCharArray());// todo
        return ds;
    }
}

I would use it like this:

Config.getDatastore().doSomthing();

Beside those un-handled exceptions, is this the correct way of using a static variable?

Answer 1

The given Config seems to indicate that this class should be a singleton, and if so, then using static variables for all members is fine. Will you have multiple Configs, or only one?

If Config isn’t intended to be a singleton, then static isn’t required in this case, or if so, only if it’s ok to share your Datastore with every instance of your Config class. You’ll achieve your goals with a simple – non-static – member variable, and you can still have, e.g. a getDataStore method. But each Config class will have it’s own Datastore

Only use static if you want to also share that Datastore among multiple instances of your Config class.