单例：如何通过反射停止创建实例

singleton reflection java

2022-09-01 00:48:17

我知道在 Java 中，我们可以通过、和 . 创建类的实例。newclone()Reflectionserializing and de-serializing

我创建了一个实现单例的简单类。

我需要停止一直可以创建我的类的实例。

public class Singleton implements Serializable{
    private static final long serialVersionUID = 3119105548371608200L;
    private static final Singleton singleton = new Singleton();
    private Singleton() { }
    public static Singleton getInstance(){
        return singleton;
    }
    @Override
    protected Object clone() throws CloneNotSupportedException {
        throw new CloneNotSupportedException("Cloning of this class is not allowed"); 
    }
    protected Object readResolve() {
        return singleton;
    }
    //-----> This is my implementation to stop it but Its not working. :(
    public Object newInstance() throws InstantiationException {
        throw new InstantiationError( "Creating of this object is not allowed." );
    }
}

在这个类中，我设法通过和停止类实例，但无法通过反射停止它。newclone()serialization

用于创建对象的我的代码是

try {
    Class<Singleton> singletonClass = (Class<Singleton>) Class.forName("test.singleton.Singleton");
    Singleton singletonReflection = singletonClass.newInstance();
} catch (ClassNotFoundException e) {
    e.printStackTrace();
} catch (InstantiationException e) {
    e.printStackTrace();
} catch (IllegalAccessException e) {
    e.printStackTrace();
}

答案 1

通过在私有构造函数中添加以下检查

private Singleton() {
    if( singleton != null ) {
        throw new InstantiationError( "Creating of this object is not allowed." );
    }
}

答案 2

像这样定义单例：

public enum Singleton {
    INSTANCE
}