将 setter 添加到单例 class

Question

我有一个这样的单身人士class

public class Service{

// SingletonHolder is a container class to hold singleton instance 
 private static final SingletonHolder<A> singleton = new SingletonHodler<>(new Service());

 private Service(){
}
  public static Service getInstance(){

//.instance() is a method in SingletonHolder to return singleton instance
    return singleton.instance();
  }

 //Method to start the Service class
  public void start(){
   // start the service
   // get the initial configuration and use the configuration value to speify a URL, something like:
   String initialConfiguration = Configuration.getSettings();
   TargetUrl = initialConfiguration.get.......
}

}

另一个 class 用于配置。 class 将初始化配置并使用 configurationUpdate() 获取更新后的配置值。

public class Configuration{


    public void configurationInitialize(){

    // initialize the configuration and get the value
    initialConfigValue = ..........    
}


   // Method to update configuration
   public void configurationUpdate(){

   // some mehtod which will get the updated configuration value
   String updateConfiguration = .............

    }    
  //method to retrun configuration settings
  public static String getSettings(){.........}
}

现在我想先获取初始配置。然后，如果配置更改，则获取 updatedValue。

我的选择之一是向服务 class 添加 setter 方法。并在Configurationclass的configurationUpdate()方法中调用setter方法，将UpdateVlaue传给那个setter.

我不确定这样做是否正确。如果我加上setter方法，它还是单例吗？这个操作会不会有什么问题？非常感谢！！！

编辑：另一个初始化class会调用配置class来初始化配置同时也会调用Service.getInstance().start()

Answer 1

I am not sure if it is the proper way to do that. If I add the setter method, is it still a singleton? Will this operation cause any problem?

还是会是单例。如果所有线程都应该使用相同的 targetUrl 那么它应该没问题。如果每个线程都应使用它自己的 targetUrl，那么 setter 更改 targetUrl 字段的值将影响所有线程。

不确定这是否是需要的，但也许它提供了一些有用的提示。

不是将配置传递给服务实例，而是通过 ThreadLocal 和静态方法使配置可用，以便服务 class 可以在需要时检索配置（请参阅配置# settingsHolder 变量和 Configuration#getSettings 方法）

注意：我没有使用 SingletonHolder，因为我不清楚它的用途（描述它的方式不提供惰性初始化，通常实例持有者用于惰性初始化目的）

public class Service {

    private static final Service INSTANCE = new Service();

    private static final ThreadLocal<TargetUrl> TARGET_URL_HOLDER = new ThreadLocal();

    private Service() {

    }

    public static Service getInstance() {
        return Service.INSTANCE;
    }

    public void start() {
        Settings initialConfiguration = Configuration.getSettings();
        TARGET_URL_HOLDER.set(initialConfiguration.getTargetUrl());
        // some more stuff before starting
    }

    public void reinitialize() {
        Settings updatedConfiguration = Configuration.getSettings();
        TARGET_URL_HOLDER.set(updatedConfiguration.getTargetUrl());
        .......
    }
}

public class Settings {
    private TargetUrl targetUrl;

    public TargetUrl getTargetUrl() {
        return this.targetUrl;
    }

    public void setTargetUrl(TargetUrl targetUrl) {
        this.targetUrl = targetUrl;
    }
}

public class Configuration {
    // use threadLocal to store the settings instance so it can be retrieved via a static method (e.g. getSettings)
    private static ThreadLocal<Settings> SETTINGS_HOLDER = new ThreadLocal<>();

    public void initialize() {

        // initialize the configuration
        Settings initialSettings = ..........
        SETTINGS_HOLDER.set(initialSettings);    
    }

    // Method to update configuration
    public void update() {
        // some method which will get the updated configuration value
       Settings updatedSettings = .............
       SETTINGS_HOLDER.set(updatedSettings);
    }

    //method to retrun configuration settings
    public static Settings getSettings() {
        return SETTINGS_HOLDER.get();
    }
}

public class Test {

    public static void main(String[] args) {
        Configuration configuration = new Configuration();
        configuration.initialize();

        Service service = Service.getInstance();
        service.start();
        // use service instance
        ...................

        configuration.update();

        service.reinitialize();

        // keep using the service instance
       .................
    }
}

根据用例，如果所有线程都必须使用相同的 targetUrl，也可以使用 AtomicReference 类型的静态变量而不是 ThreadLocal

类型的静态变量来实现它

将 setter 添加到单例 class

Add setter to an singleton class

java

singleton

getter-setter