【笔记】Java的单例模式最佳实践

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前言

Java的单例模式最佳实践

getInstance()

public class Singleton implements Serializable {
    
    private static final long serialVersionUID = 1L;

    private static class Holder {
        private static final Singleton INSTANCE = new Singleton();
    }

    private Singleton() {
        // 防反射攻击：第二次调用构造器时抛异常
        if (Holder.INSTANCE != null) {
            throw new IllegalStateException("单例已存在，禁止反射创建");
        }
    }

    // 防序列化破坏
    protected Object readResolve() {
        return Holder.INSTANCE;
    }

    public static Singleton getInstance() {
        return Holder.INSTANCE;
    }

    public void method() {
        System.out.println();
    }
}

// 调用方式
public class Client {
    public static void main(String[] args) {
        Singleton.getInstance().method();
    }
}

INSTANCE

public enum Singleton {
    INSTANCE;

    // 可选的业务字段
    private String config;

    public void init(String config) {
        this.config = config;
    }

    public static Singleton getInstance() {
        return INSTANCE;
    }

    public void method() {
        System.out.println();
    }
}

// 调用方式
public class Client {
    public static void main(String[] args) {
        Singleton.INSTANCE.init("production");
        Singleton.INSTANCE.method();
    }
}

完成