如何破解静态内部类实现的单例模式?

如何破解静态内部类实现的单例模式?

public class Singleton {
    private static class SingletonHolder {
        private static Singleton instance = new Singleton();
    }
    private Singleton() {}
    public static Singleton getInstance() {
        return SingletonHolder.instance;
    }
}

(1)反射破坏单例

public static void main(String[] args) throws Exception {
    Singleton singleton = Singleton.getInstance();
    Constructor<Singleton> constructor = Singleton.class.getDeclaredConstructor();
    constructor.setAccessible(true);
    Singleton newSingleton = constructor.newInstance();
    //运行结果:false
    System.out.println(singleton == newSingleton);
}

(2)反序列化破坏单例

引入依赖：

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.8.1</version>
</dependency>

这个依赖提供了序列化和反序列化工具类。

Singleton类实现java.io.Serializable接口。

如下：

public class Singleton implements Serializable {
    private static class SingletonHolder {
        private static Singleton instance = new Singleton();
    }
    private Singleton() {}
    public static Singleton getInstance() {
        return SingletonHolder.instance;
    }
    public static void main(String[] args) {
        Singleton instance = Singleton.getInstance();
        byte[] serialize = SerializationUtils.serialize(instance);
        Singleton newInstance = SerializationUtils.deserialize(serialize);
        //运行结果:false
        System.out.println(instance == newInstance);
    }
}