我正在尝试通过添加 readResolve() 方法来编写一个可序列化的单例类。我的意图是在序列化时获得与其对象状态相同的对象。
下面是我的测试示例代码:
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
public class SingletonDemo {
public static void main(String[] args) {
Singleton obj = Singleton.getInstance();
System.out.println("After NEW Object creation : " + obj);
obj.i = 5;
System.out.println("Object modified");
System.out.println("After Object 1st Modification : " + obj);
serializeMe();
System.out.println("Serialized successfully with object state : " + obj);
obj.i = 10;
System.out.println("Object modified again");
System.out.println("After Object 2nd Modification : " + obj);
Singleton st = (Singleton)deSerializeMe();
System.out.println("Deserialized successfully");
System.out.println("After Deserialization : " + st);
}
public static void serializeMe() {
ObjectOutputStream oos = null;
try {
oos = new ObjectOutputStream(new FileOutputStream("d:\\SingletonData.txt"));
oos.writeObject(MySerializedSingleton.getInstance());
} catch (IOException e) {
e.printStackTrace();
}
}
public static Object deSerializeMe() {
ObjectInputStream oin = null;
Object obj = null;
try {
oin = new ObjectInputStream(new FileInputStream("d:\\SingletonData.txt"));
obj = oin.readObject();
} catch (IOException | ClassNotFoundException e) {
e.printStackTrace();
}
return obj;
}
}
class Singleton implements Serializable {
int i;
private static Singleton obj = null;
private Singleton() {
System.out.println("Executing constructor");
i=1;
}
public static Singleton getInstance() {
if(obj == null) {
obj = new Singleton();
}
System.out.println("An instance is returned");
return obj;
}
/*private void writeObject(ObjectOutputStream oos) {
try {
oos.writeInt(i);
} catch (Exception e) {
e.printStackTrace();
}
}
private void readObject(ObjectInputStream ois) {
try {
i = ois.readInt();
} catch (Exception e) {
e.printStackTrace();
}
}*/
public Object readResolve() {
System.out.println("Executing readResolve");
return Singleton.getInstance(); // FIXME
}
@Override
public String toString() {
return "Singleton [i=" + i + "]";
}
}
输出:
Executing constructor
An instance is returned
After NEW Object creation : Singleton [i=1]
Object modified
After Object 1st Modification : Singleton [i=5]
An instance is returned
Serialized successfully with object state : Singleton [i=5]
Object modified again
After Object 2nd Modification : Singleton [i=10]
Executing readResolve
An instance is returned
Deserialized successfully
After Deserialization : Singleton [i=10]
我知道当前场景将始终返回具有最新对象状态的同一个单例实例。
我尝试覆盖 writeObject() 和 readObject() (在上面的代码中注释)但没有得到想要的结果。IE
After Deserialization : Singleton [i=5]
但是 readResolve() 中没有 ObjectInputStream 的引用,因此我可以在返回之前获取实例并使用序列化对象的状态对其进行更新。
如果我的概念有误,请纠正我并帮助我解决这个问题。
谢谢。