Instantiate service layer and repositories once during life of web application

During the life of my web application I know all of my services and repositories will be called. I would like to instantiate them once during the startup of the web application and refer to the instantiated references in my code.

Is there a common pattern for instantiating your services/repositories only once during the lifetime of a web application without making them static or singletons.

I would like to avoid making my services/repositories static classes or singletons for testability however instantiating them on every web request do开发者_如何学Cesn't seem right when they are designed to be stateless and I know they will all be needed during the lifetime of the application.

I am using c#/asp.net.

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The concept you need is called IoC / DI, and there are many frameworks for this. When you have a class like CustomerService and you need a CustomerRepository in it, by definition that is a dependancy, and you should pass it through the constructor of CustomerService - but then there is the question where you will instantiate CustomerService? Well, who uses that service should get it through constuctor too, it is maybe a CustomerPresenter, or some other class, irrelevant. My point is that with doing dependancy injections you structure your code to a very single point where an IoC / DI framework resolves those dependancies accoring to your rules.

At the very top of the program, you would have something like:

ICustomerPresenter presenter = IoC.Resolve<ICustomerPresenter>();

and everything will automatically come together behind the scenes.

To achieve this, here is an example with StructureMap:

For<ICustomerPresenter>().Use<CustomerPresenter>();
For<ICustomerService>().Singleton().Use<CustomerService();
For<ICustomerRepository>().Singleton().Use<CustomerRepository>();

With this, you keep the testability. I've simplified things a lot here, so this isn't much usable as-is, but there are plenty IoC / DI resources online, so check them out.

Note: for web applications you will want to check out handling lifecycle per request, you will rarely have singletons for entire web application.

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Dependency Injection frameworks will take care of the lifetime of your objects.

Eg

container.RegisterType<MyService>().Singleton();

There are many DI frameworks choose what suits you best.