Struts1 single case mode, struts2 non-single case mode

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First of all, what is called the single case mode bar:

How to make a class in Java, can only instantiate once. The
answer is: Single case mode.

the specific code is reflected in the public
class a{

    Private A () {}//The constructor to private, other classes can no longer invoke the instantiated

    Private static A Instance=new a ()//unique instance, plus static property

    public static A getinstance () {//Other class calls the unique entry of a, also the static property, called by A.getinstance ()

        return instance;

    }

}

"The Struts1 action is a singleton pattern and must be thread-safe because only one instance of the action handles all requests." A single example strategy limits what Struts1 action can do, and is particularly cautious when developing. The action resource must be thread safe or synchronized. 

Action execution Control: "STRUTS1 supports a separate request processors (lifecycle) for each module, but all the action in the module must share the same life cycle." "STRUTS2 supports creating a different lifecycle for each action through the Interceptor Stack (Interceptor Stacks). The stack can be used in conjunction with different action as needed.