不使用单例的类之间共享数据的方法

Question

I am working on library that is used in application (as Maven artifact). In my current situation library has a main class that provides static methods for working with it. Therefore it allows only "one instance" work mode with this library. At the beginning of work it is necessary to provide Configuration object to this main class. Such as MainClass.start(new Configuration()) and later on this configuration object is accessed by other classes via singleton factory.

My problem currently is that I need to change library in a way that it should allow multi-instance mode. Such that MainClass won't have any more static methods, and will have to be instantiated. What I stumble upon is how do I then provide each instance with its unique Configuration in a way that instances of other classes (those that are used together with current instance of MainClass) can also access it while not having direct access to instance of MainClass. Of course in this scenario Singleton isn't a solution because two or more MainClass instances should have each own configuration.

Answer 1

class Configuration{
 String a;
 String b;

 public Configuration(String a, String b){
  this.a = a;
  this.b = b;
 }

 public String getA(){
  return a;
 }

 public String getB(){
  return b;
 }

}


class MainClassFactory{
 private final static MainClassFactory INSTANCE = new MainClassFactory();
 private ConcurrentHashMap<String,MainClass> mainClassMap = new ConcurrentHashMap<String,MainClass>();
 public static getInstance(){
  return INSTANCE;
 }

 public MainClass getMainClass(Configuration config){
  String key = config.getA() +","+ config.getB();
  MainClass mainClass = mainClassMap.get(key);
  if(mainClass == null){
   mainClass = new MainClass(config);
   mainClassMap.put(key,mainClass);
  }
  return mainClass;
 }

}

Will this help you ?

Assuming the MainClass instantiate with Configuration then by calling MainClassFactory.getInstance().getMainClass(config) you will be able to get the same MainClass by "same" configuration (the "same" here means the value of a and b are the same)

The idea is simple: use a key with can represent the characteristic of the Configuration and cache the MainClass using a Map with this key. Finally return the same object when providing configuration with same characteristic;