第 90 条：考虑用序列化代理代替序列化实例

考虑用序列化代理代替序列化实例.jpeg

// Serialization proxy for Period class
private static class SerializationProxy implements Serializable {
    private final Date start;
    private final Date end;
    SerializationProxy(Period p) {
        this.start = p.start;
        this.end = p.end;
    }
    private static final long serialVersionUID = 234098243823485285L; // Any number will do (Item 87)

    // readResolve method for Period.SerializationProxy
    private Object readResolve() {
        return new Period(start, end); // Uses public constructor
    }

}


// writeReplace method for the serialization proxy pattern
private Object writeReplace() {
    return new SerializationProxy(this);
}


// readObject method for the serialization proxy pattern
private void readObject(ObjectInputStream stream) throws InvalidObjectException {
    throw new InvalidObjectException("Proxy required");
}

EnumSet

// EnumSet's serialization proxy
private static class SerializationProxy <E extends Enum<E>> implements Serializable {
    // The element type of this enum set.
    private final Class<E> elementType;
    // The elements contained in this enum set.
    private final Enum<?>[] elements;
    SerializationProxy(EnumSet<E> set) {
        elementType = set.elementType;
        elements = set.toArray(new Enum<?>[0]);
    }
    private Object readResolve() {
        EnumSet<E> result = EnumSet.noneOf(elementType);
        for (Enum<?> e : elements)
            result.add((E)e);
        return result;
    }
    private static final long serialVersionUID = 362491234563181265L;
}