I am making a database to store information about the users of my website (I am using stuts2 and hence Java EE technology). For the database I'll be making a DBManager. Should I apply singleton pattern here or rather make all it's methods static?
I will be using this DBManager for basic things like adding, deleting and updating User profiles. Along with it, I'll use for all other querying purposes, for instance to find out whether a username already exists and to get all users for administrative purposes and stuff like that.
My questions
- What is the benefit of singleton pattern?
- Which thing is most apt here? All static methods or a singleton pattern?
- Please compare both of them.
regards
shahensha
P.S. The database is bigger than this. Here I am talking only about the tables which I'll be using for storing User Information.
Should I apply singleton pattern here or rather make all its methods static?
None of both. Just create one.
In a simple servletcontainer, you can use ServletContextListener for this. During webapp's startup, create one and put it in the application scope by ServletContext#setAttribute(). It'll be available to all servlets during webapp's lifetime. For a basic kickoff example, you may find this article useful.
I don't know the internals of EE, but typically the difference between a static class and a Singleton is instantiation - with the static class, there is no actual instantiation, no member data, no reference to an object. So the practical difference is...not much.
I think the real benefit here is conceptual...static methods and properties are methods which apply to the abstract concept of the class, and not to a particular instance. If you create a singleton user object here, who is that user? Why does he have the particular context to create and update profiles? I don't think the concept maps very well.
It makes much more sense to me to say UserProfile.Update(username, password, firstName...). You're saying "perform the task Update from the abstract concept of UserProfile on this particular set of data".
Keep in mind here that my use of the word abstract is strictly figurative, and not in the computer science sense of the word.
Not much practical difference, but somewhat of a philosophical difference.
I would recommend the singleton approach here - you're really describing a type of Data Access Object (DAO), albeit at a high level.
Some thoughts on why:
A Factory style approach to creation of the DBManager itself (i.e., DBManagerFactory) would make unit testing easier; it lends itself to the dependency injection model.
A class with a bunch of static methods is generally assumed to be a switchblade/utility kind of class with no over-arching theme (i.e., independence between methods). Think of a class like StringUtils -- people assume that there's no general state to the class.
At a crass level, with the "all static methods" approach, you're creating a lot of work for yourself in that you need to keep typing static for every method. Again, you can just have a DBManagerFactory that simply has a single static method for creating the DBManager, which ends up being a singleton.
来源：https://stackoverflow.com/questions/4618212/what-is-the-difference-between-all-static-methods-and-applying-a-singleton-patte