设计模式单例模式防止反射漏洞攻击

// *****************************现象描述*******************************

package com.example.SpringBootTest1.shejimoshi.singleton;
public class InnerclassSingleton {
    private InnerclassSingleton() {};
    private static class Singleton {
        private static final InnerclassSingleton i = new InnerclassSingleton();
    }

    public static InnerclassSingleton getInstance() {
        return Singleton.i;
    }
}

// 通过反射获取对象拿到的对象不是同一个

public class Test {
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        Constructor<InnerclassSingleton> declaredConstructor = InnerclassSingleton.class.getDeclaredConstructor();
        declaredConstructor.setAccessible(true);
        InnerclassSingleton instance1 = declaredConstructor.newInstance();
        InnerclassSingleton instance2 = InnerclassSingleton.getInstance();
        System.out.println(instance1 == instance2); // false
    }
}

// *********************************防止漏洞攻击*****************************

package com.example.SpringBootTest1.shejimoshi.singleton;
public class InnerclassSingleton {
    private InnerclassSingleton() {
        if (InnerclassSingleton.getInstance() != null) {
            throw new RuntimeException("单例模式不允许创建多个实例");
        }
    };

    private static class Singleton {
        private static final InnerclassSingleton i = new InnerclassSingleton();
    }

    public static InnerclassSingleton getInstance() {
        return Singleton.i;
    }
}

// 运行这段代码通过反射去创建实例时会报自定义异常, 从而达到防止反射漏洞攻击

public class Test {
    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        Constructor<InnerclassSingleton> declaredConstructor = InnerclassSingleton.class.getDeclaredConstructor();
        declaredConstructor.setAccessible(true);
        InnerclassSingleton instance1 = declaredConstructor.newInstance();
        InnerclassSingleton instance2 = InnerclassSingleton.getInstance();
        System.out.println(instance1 == instance2);
    }
}