Can I change member variable type of serializable class?

Suppose a class implements serializable and I serialize an object of the class. After ding so I change internal implementation such that I change data type of one the variable from int to String.. Is it possible to obtain the values from the serialized object while deserialization using readresolve?

Class A implements Serializable{ private int first; private int second; }

after the serialization:

Class A implements Serializable{ private int first; private String second; }

-------------Problems Reply------------

You'd need to implement a custom readObject() method. More info here.

The serialVersionUID would also need to be the same in both versions of the class. If you don't already declare a serialVersionUID then the jvm will calculate it based on the shape of the class. For this to work you would need to explicitly declare the old serialVersionUID in the new version of the class. More info here

Bored. Let's try this (not compiled)...


class A implements Serializable {
private static final long serialVersionUID = 0x...L;
private static final ObjectStreamField[] serialPersistentFields = {
new ObjectStreamField("first", int.class),
new ObjectStreamField("second", int.class),
new ObjectStreamField("secondString", String.class),
private int first;
private String second;

private void writeObject(ObjectOutputStream out) throws IOException {
ObjectOutputStream.PutField fields = out.putFields();
fields.put("first", first);
int secondInt;
try {
secondInt = Integer.parseInt(second);
} catch (NumberFormatException exc) {
secondInt = -1;
fields.put("second", secondInt);
fields.put("secondString", second);
private void readObject(
ObjectInputStream in
) throws IOException, ClassNotFoundException {
ObjectInputStream.GetField fields = out.readFields();
fields = fields.get("first", 0);
int secondInt = fields.get("second", 0);
second = (String)field.get("secondString", Integer.toString(secondInt));

If either of the fields were final, then you'd need readResolve weirdness or worse.

(Almost left the last secondInt as second there. Boo hiss to String.valueOf.)

Category:java Views:0 Time:2019-01-10

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