这种方式仍然存在并发的同步阻塞问题,并且jdk1.5之前是有问题的
public class SeriSingleDCL { // volatile 多线程并发的可见性 private volatile static SeriSingleDCL single = null; private SeriSingleDCL() { } /** * DCL方式减少同步的阻塞 */ public static SeriSingleDCL getInstance() { if (single == null) { synchronized (SeriSingleDCL.class) { if (single == null) { single = new SeriSingleDCL(); return single; } } } return single; } }
于是就有了静态内部类的方式&序列化单例问题解决(readResolve方法重写)
public class SeriSingle implements Serializable { private static SeriSingle seriSingle; /** * 被调用的时候才会被加载,实现延迟初始化 */ private static class SeriSingleHolder { // static jvm保证初始化的多线程可见性 private static SeriSingle instance = new SeriSingle(); } public static SeriSingle getInstance() { return SeriSingleHolder.instance; } /** * 反序列化会调用这个方法,从而保证单例模式的单例性 * 否则反序列化的时候会生成另一个对象 */ private Object readResolve() { return SeriSingle.getInstance(); } }
class Test { public static void main(String[] args) throws IOException, ClassNotFoundException { File file = new File("/Users/***/test/seritest.obj"); ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file)); oos.writeObject(SeriSingle.getInstance()); oos.close(); ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file)); SeriSingle readObject = (SeriSingle) ois.readObject(); ois.close(); //如果没有实现SeriSingle#readResolve()方法,这将使两个对象 System.out.println(readObject == SeriSingle.getInstance()); } }