Over a million developers have joined DZone.

Serialization Proxy Pattern Example

· Java Zone

Navigate the Maze of the End-User Experience and pick up this APM Essential guide, brought to you in partnership with CA Technologies

There are books, which change your life immensely. One of such books is "Effective Java" by Joshua Bloch. Below you may find small experiment, which was inspired by Chapter 11 of this book - "Serialization".

Suppose that we have a class designed for inheritance, which is not Serializable itself, and has no parameterless constructor, like in this example:
public class CumbersomePoint {

    private String name;

    private double x;

    private double y;

    protected CumbersomePoint(double x, double y, String name) {
        this.x = x;
        this.y = y;
        this.name = name;

    public String getName() {
        return name;

    public double getX() {
        return x;

    public double getY() {
        return y;

Now when we extend this class, for example in following way:
public class ConvenientPoint extends CumbersomePoint implements Serializable {

    public ConvenientPoint(double x, double y, String name) {
        super(x, y, name);

and try to serialize and then deserialize any of ConvenientPoint instances, we'll quickly encounter beautifulInvalidClassException, complaining that there is no valid constructor. Situation looks kinda hopeless, until you apply technique known as Serialization Proxy Pattern.

We will start by adding to the ConvenientPoint class following inner class:
private static class SerializationProxy implements Serializable {

        private String name;

        private double x;

        private double y;

        public SerializationProxy(ConvenientPoint point) {
            this.name = point.getName();
            this.x = point.getX();
            this.y = point.getY();

        private Object readResolve() {
            return new ConvenientPoint(x, y, name);

The SerializationProxy class will represent the logical state of enclosing class instance. We will have to add also following method to ConvenientPoint class:
   private Object writeReplace() {
        return new SerializationProxy(this);

Now when the ConvenientPoint instance will be serialized, it will nominate its replacement, thanks to writeReplacemethod - SerializationProxy instance will be serialized instead of ConvenientPoint.

From the other side, when SerializationProxy will be deserialized, readResolve method usage will nominate its replacement, being ConvenientPoint instance.

As you see, we've made ConvenientPoint serializable, regardless of missing parameterless constructor of non-serializable parent class.

One more remark, at the end of this post - if you want to protect against breaking class invariants, enforced by the constructor, you may add following method to class using Serialization Proxy Pattern (ConvenientPoint in our example): 
   private void readObject(ObjectInputStream stream) throws InvalidObjectException {
        throw new InvalidObjectException("Use Serialization Proxy instead.");
It will prevent deserialization of the enclosing class.

Thrive in the application economy with an APM model that is strategic. Be E.P.I.C. with CA APM.  Brought to you in partnership with CA Technologies.


Published at DZone with permission of Michal Jastak, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}