Question

I’m using a simple struct where I store readonly values (like properties with no setter in C#). To achieve this I’m using public final int test=42;.

For some reasons I want to allow to serialize this class. I’m using this code:

private void writeObject(ObjectOutputStream oos) throws IOException {
    oos.writeInt(test);
}
private void readObject(ObjectInputStream ois) throws IOException {
    test=ois.readInt();
}

The last one does not work because the field test is final how can I solve this issue?

Answer 1

You can use reflection to modify the value of test

// Get the Class object for the class of which test is a field
Class<?> myClass = MyClass.class;

// We will need to set test as accessible so as to change it's value
// Get the Field object for test
Field testField = myClass.getDeclaredField("test");
// Save the current accessibility of test
boolean wasAccessible = testField.isAccessible();
// Mark test as accessible
testField.setAccessible(true);
// Set the value of test for this instance of MyClass
int newTestValue = 42;
testField.setInt(this, newTestValue);
// Restore the accesibility of test to it's original
testField.setAccessible(wasAccessible);

The above assumes that your application has the permissions given by the SecurityManager to use reflection. If it does not, the SecurityManager will throw an exception.