使单例成为Spring bean的正确方法 [英] Correct way of making a singleton a Spring bean

问题描述

我正在将单例转换为Spring bean，因此如果单例无法初始化，则整个Web应用程序的spring上下文无法正确加载。

I am converting a singleton to a Spring bean, so that if the singleton fails to initialize, then entire web application's spring context doesn't load properly.

使Spring上下文无法正确加载的好处是人们会在部署过程中注意并修复配置。与使用'非spring bean'单例相反：当在初始化期间抛出异常时，没有人注意到..直到实际用户抱怨缺少功能。

The advantage of making the Spring context not load properly, is that people will take notice and fix the configuration during deployment itself. As opposed to using 'non-spring bean' singleton: when that throws exception during initialization, nobody notices.. until a actual user complains of missing functionality.

我的更改是按预期工作..但我不确定我做的是否正确。

有什么想法吗？

My changes are working as expected.. but I am not sure if I am doing the right thing.
Any thoughts?

代码如下：

public class MySingleton {

    private static MySingleton INSTANCE = null;
    private MySingleton(){}


public static MySingleton getInstance(){
    if(INSTANCE == null){
        synchronized(MySingleton.class){
            if(INSTANCE == null){
                try{
                    doWork()
                }catch(Exception e){
                    throw new IllegalStateException("xyz", e);
                }
                INSTANCE = new MySingleton();
            }
        }
    }

    return INSTANCE;
}

private static void doWork() {
    // do some work
    }

}

在spring config xml中，bean将被定义为：

And in the spring config xml, the bean will be defined as:

<bean id="MySingletonBean"
    class="com.MySingleton"
    factory-method="getInstance" lazy-init="false" singleton="true">
</bean>

注意：
大部分内容类似于策略在本文中讨论：
http：// springtips。 blogspot.com/2007/06/configuration-hell-remedy-with.html

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编辑1：

使用这个单例的类不是spring bean本身..它们只是非弹簧pojos，我无法转换为spring。他们必须依靠getInstance（）方法来获取Singleton。

The classes that use this singleton, are not spring beans themselves.. they are just non-spring pojos, that I can't convert to spring. They must rely on getInstance() method get hold of the Singleton.

编辑2： （将我在下面的评论复制到此说明部分）
我试图针对两件事：

Edit 2: (copying a comment I made below into this description section) I am trying to target two things:

1. 我想要Spring初始化单身人士。因此，如果
   初始化失败，则应用程序加载失败。


2. 我希望其他类能够使用类而不必依赖contextAwareObj.getBean（MySingleton）

---

编辑3（最终）：
我决定让这个班级成为单身人士......而且我不是把它变成一个春天的豆子。如果它无法初始化，它将在日志文件中记录一些内容..希望进行部署的人注意到....我放弃了我之前提到的方法，因为我觉得它将来会造成维护噩梦，所以我不得不选择 - 单身 - 或 - 春豆。我选择了单身。

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EDIT 3 (FINAL): I decided to make this class a singleton.. and am not making it a spring bean. If it fails to initialize, it will log something in the Log file.. hopefully the person doing deployment takes notice.... I abandoned the approach I mentioned earlier because I feel it will create a maintenance nightmare in future, so I had to pick between - singleton - or - spring bean. I chose singleton.

推荐答案

你必须宣布 INSTANCE 字段为 volatile ，以便双重检查锁定才能正常工作。

You must declare the INSTANCE field as volatile for double-checked locking to work correctly.

参见有效的Java ，项目71 。

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