Java – Using spring to Avoid Singleton pattern

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Considering that Spring framework can manage pretty everything related to object creation (life cycle, object scope ..), is it longer necessary to use singleton pattern in an application using the framework, or are there still situations when we need to use Singleton pattern instead of singleton instance created by Spring?

One of the problem of using the singleton pattern is global state. Is the problem avoided using the Spring-defined singleton scope?

Best Answer

"One of the problem of using the singleton pattern is global state"

If you use it for global state then you can do so. But that does not affect the "singleton pattern" itself as it is answering the question how many instances of an object there may be: One.

"global" and "state" do not adress the question "How many instances may be there?". They adress the questions "What is the scope?" and "May data change?" (mutability).

Spring will manage singletons for you. But the scope and mutability is up to you to define.

Related Solutions

Design Patterns – Alternatives to the Singleton Pattern

Your second option is a fine way to go -- it's a kind of dependency injection, which is the pattern used to share state across your program when you want to avoid singletons and global variables.

You can't get around the fact that something has to create your factory. If that something happens to be the application, so be it. The important point is that your factory shouldn't care what object created it, and the objects that receive the factory shouldn't depend on where the factory came from. Don't have your objects get a pointer to the application singleton and ask it for the factory; have your application create the factory and give it to those objects that will need it.

C++ – Is there something like a polymorphic Singleton

What you want sounds like a good case for the Factory pattern. You would write something like:

class LoaderFactory {
  public Loader getLoader() {
    if (environment1) return ZipLoader.getInstance();
    else if (environment2) return DiskLoader.getInstance();
    else return SomeOtherLoader.getInstance();
  }
}

Each type of Loader class is a singleton, and each should implement the Loader interface. Your LoaderFactory performs the logic that determines which type is appropriate to return.

Best Answer

Related Solutions

Design Patterns – Alternatives to the Singleton Pattern

C++ – Is there something like a polymorphic Singleton

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