java - 如何维护序列化对象的单例状态？

Question

如果我将“A”类定义为单例，则意味着我只能创建“A”类的一个对象。如果我将它设为可序列化并序列化，那么如何实现同一对象的单例状态？

Answer 1

引用 Effective Java #77，你应该看看实现 readResolve 方法。

The readResolve feature allows you to substitute another instance for the one created by readObject [Serialization, 3.7]. If the class of an object being deserial- ized defines a readResolve method with the proper declaration, this method is invoked on the newly created object after it is deserialized. The object reference returned by this method is then returned in place of the newly created object. In most uses of this feature, no reference to the newly created object is retained, so it immediately becomes eligible for garbage collection.

public class Elvis implements Serializable {
public static final Elvis INSTANCE = new Elvis();
// readResolve for instance control - you can do better!
private Object readResolve() {
//Return the one true Elvis and let the garbage collector
// take care of the Elvis impersonator.
return INSTANCE;
}
}