Singleton class with updated parameters in java - class

Question

public class ThreadSafeSingleton implements Serializable {
#Override
public String toString() {
return "ThreadSafeSingleton [i=" + i + ", str=" + str + "]";
}
int i;
String str;
private static ThreadSafeSingleton instance;
public int getI() {
return i;
}
public void setI(int i) {
this.i = i;
}
public String getStr() {
return str;
}
public void setStr(String str) {
this.str = str;
}
private ThreadSafeSingleton(){
}
public static synchronized ThreadSafeSingleton getInstance(int i,String str){
if(instance == null){
synchronized (ThreadSafeSingleton.class) {
if(instance == null){
instance = new ThreadSafeSingleton();
}
}
}
instance.setI(i);
instance.setStr(str);
return instance;
}
public Object readResolve(){
System.out.println("readResolve executed");
return getInstance(this.i,this.str);
}
public static void main(String[] args) throws IOException, Exception {
FileOutputStream fos = new FileOutputStream(
"B://Serilization//text1.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
ThreadSafeSingleton obj = new ThreadSafeSingleton();
obj.setI(1);
obj.setStr("katrina kaif");
oos.writeObject(obj);
System.out.println("serilization done");
FileInputStream fis = new FileInputStream("B://Serilization//text1.txt");
ObjectInputStream ois = new ObjectInputStream(fis);
ThreadSafeSingleton copy=(ThreadSafeSingleton) ois.readObject();
System.out.println("copy "+copy);
System.out.println("deserilization done");
}
}
in the above code i have a singleton class containing int i and String str attributes and i have implemented Serializable interface my requirement is that when i serialized a class i will serialize the class with some attributes values on one JVM and when i deserialize on another JVM i should get the same instance of my singleton class but the attributes in the class should get updated with the values i provided during serialization
here on internet i checked the solution i got to use readResolve method there you can write a logic which will set the values of attributes i provided during serialization of my singleton class so if you will see the code of readResolve i have written a code like this "return getInstance(this.i,this.str);" here i have used "this" keyword which means a current object is being used therefore i have question
i have doubt that is this code creating new object here as "this" refers to the current object apart from the object i created in the getInstance(int i,String str) method can anybody please explain is this breaking singleton ?

Answer 1

You may want to read up on Java serialization: readObject() vs. readResolve(). When readResolve() is called, your object has already been deserialized from the stream and fully created. Your this pointer, in that case, will be the object that the deserialization process has constructed, complete with the i and str values from the stream. If you use this.i and this.str to construct the new Singleton, you're not creating a new object with the new JVM's specific parameters.