单例模式实现方式比较

单例模式实现方式	线程安全	延迟加载	反射安全	序列号安全
饿汉模式	√	×	×	×
懒汉模式（非空判断）	×	√	×	×
懒汉模式（方法加锁）	√	√	×	×
懒汉模式（双重检查锁）	√	√	×	×
静态内部类	√	√	×	×
枚举	√	√	√	√

/**
 * 饿汉
 * @author bell.zhouxiaobing
 *
 */
public class Singleton implements Serializable{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	
	private Singleton() {
	}
	private static Singleton SINGLETON = new Singleton();
	public static Singleton getInstance() {
		return SINGLETON;
	}
}

/**
 * 懒汉-非线程安全
 * @author bell.zhouxiaobing
 *
 */
public class Singleton implements Serializable{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	
	private Singleton() {
	}
	private static Singleton SINGLETON;
	public static Singleton getInstance() {
		if (SINGLETON == null) {
			SINGLETON = new Singleton();
		}
		return SINGLETON;
	}
}

/**
 * 懒汉-线程安全
 * @author bell.zhouxiaobing
 *
 */
public class Singleton implements Serializable{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private Singleton() {
	}
	private static Singleton SINGLETON;
	public static synchronized Singleton getInstance() {
		if (SINGLETON == null) {
			SINGLETON = new Singleton();
		}
		return SINGLETON;
	}
}

/**
 * 懒汉-双重校验锁
 * @author bell.zhouxiaobing
 *
 */
public class Singleton implements Serializable{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private Singleton() {
	}
	private volatile static Singleton SINGLETON;// 内存可见性 
	public static  Singleton getInstance() {
		if (SINGLETON == null) {
			synchronized (Singleton.class) {//synchronized 原子性 有序性 内存可见性
				if (SINGLETON == null) {
					SINGLETON = new Singleton();
				}
			}
		}
		return SINGLETON;
	}
}

/**
 * 静态内部类
 * @author bell.zhouxiaobing
 *
 */
public class Singleton implements Serializable{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	private Singleton() {
	}
	private static class Inner{
		private static Singleton SINGLETON = new Singleton();
	}
	
	public static  Singleton getInstance() {
		return Inner.SINGLETON;
	}
}

/**
 * 枚举
 * @author bell.zhouxiaobing
 *
 */

public enum Singleton implements Serializable{
	SINGLETON;
	// 可以防止使用 反射 来生成新对象
	// 可以防止使用 序列化 方式生成新对象
}

public class SingletonTest {
	public static void main(String[] args) throws Exception {
		Singleton instance = Singleton.getInstance();
		System.out.println(instance);
		// 拿到所有的构造函数，包括非public的
        Constructor<Singleton> constructor = Singleton.class.getDeclaredConstructor();
        constructor.setAccessible(true);
        // 使用空构造函数new一个实例。即使它是private的~~~
        Singleton sReflection = constructor.newInstance();
        System.out.println(sReflection);
        System.out.println(instance == sReflection);
       
	}
}

public class SingletonSerializableTest {
    // Singleton类需要实现Serializable序列化接口
	public static void main(String[] args) throws Exception {
		Singleton s = Singleton.getInstance();

        byte[] serialize = SerializationUtils.serialize(s);
        Object deserialize = SerializationUtils.deserialize(serialize);

        System.out.println(s);
        System.out.println(deserialize);
        System.out.println(s == deserialize);
	}
}