Alternatives to needing class file during deserialization?

Question

Hi,
I'm trying to find a way of deserializing an object without requiring its class file (eg, class A) to be present. In that case the JVM instance that's deserializing an instance of class A wouldn't need to worry about needing to access the class A from its classpath (file "A.class") or from any other source (such as a custom classloader loading class A's bytecodes over the network) in order to deserialize an instance of class A, except when the source is the serialization stream itself -- all data needed for serialization would be contained only within the serialization stream.
I believe this should be doable by first serializing an instance of class java.lang.Class that represents class A (since java.lang.Class instances are serializable), and then serializing the instance of class A, as explained below. This technique isn't working, and I'm wondering if anyone knows why, and if there are other known techniques for accomplishing the same objective.
I start out with these classes as a test that serialization is working:
The class whose instance I'm serializing/deserializing:
class A implements java.io.Serializable {
     public int x = 5;
}Serialization code:
import java.io.*;
class Serialize {
     public static void main(String[] args) throws Exception {
          FileOutputStream fos = new FileOutputStream("a.ser");
          ObjectOutput out = new ObjectOutputStream(fos);
          A aRef = new A();
          out.writeObject(aRef);
          out.flush();
          out.close();
}Deserialization code:
import java.io.*;
class Deserialize {
     public static void main(String[] args) throws Exception {
          FileInputStream fis = new FileInputStream("a.ser");
          ObjectInput in = new ObjectInputStream(fis);
          A aRef = (A)in.readObject();
          in.close();
          System.out.println(aRef.x); //expect 5
}Here's what I do:
(1) javac A.java Serialize.java Deserialize.java
(2) java Serialize
(3) java Deserialize
This works fine, and prints "5" as expected.
Now that I know that this base case works, I next try to serialize an instance of class java.lang.Class into the stream. This instance will represent class A, and can be obtained by specifying the literal "A.class" in the source code as shown below. Then I serialize an instance of class A as before. I'll then repeat step (1) and (2), erase the "A.class" file, and then do step 3. Here's the new code:
The class whose instance I'm serializing/deserializing (same as before):
class A implements java.io.Serializable {
     public int x = 5;
}Serialization code:
import java.io.*;
class Serialize {
     public static void main(String[] args) throws Exception {
          FileOutputStream fos = new FileOutputStream("a.ser");
          ObjectOutput out = new ObjectOutputStream(fos);
          Class clazz = A.class;
          out.writeObject(clazz);
          A aRef = new A();
          out.writeObject(aRef);
          out.flush();
          out.close();
}Deserialization code:
import java.io.*;
class Deserialize {
     public static void main(String[] args) throws Exception {
          FileInputStream fis = new FileInputStream("a.ser");
          ObjectInput in = new ObjectInputStream(fis);
          Class clazz = (Class)in.readObject(); //shouldn't this cause class A to be loaded?
          A aRef = (A)in.readObject();
          in.close();
          System.out.println(aRef.x); //expect "5"
          System.out.println(clazz); //expect "class A"
}And now the revised steps:
(1) javac A.java Serialize.java Deserialize.java
(2) java Serialize
*(3) Delete the "A.class" file because it shouldn't be needed since we're now serializing an instance of class Class that should fully represent class A.*
(4) java Deserialize
Bam... exception thrown at step 4:
Exception in thread "main" java.lang.ClassNotFoundException: A
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClassInternal(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at java.io.ObjectInputStream.resolveClass(Unknown Source)
        at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
        at java.io.ObjectInputStream.readClassDesc(Unknown Source)
        at java.io.ObjectInputStream.readClass(Unknown Source)
        at java.io.ObjectInputStream.readObject0(Unknown Source)
        at java.io.ObjectInputStream.readObject(Unknown Source)
        at Deserialize.main(Deserialize.java:6)Why is a ClassNotFoundException thrown? Class A is already loaded automatically after the instance of class Class is deserialized, isn't it? It's possible that an instance of class Class doesn't store method bytecodes -- I'm not sure about that. But even so, I purposefully did not include any methods in class A -- I just made the data member public (bad form, but this is just a test).
Any ideas why this isn't working, or a way(s) to accomplish the goal?
Thanks,
Will

Answer 1

serializing java.lang.Class instance does not really write the content of the class file in to the stream. It only write a class descriptor. At the read end it will try to locate the class file locally and validate the class file with the information in the descriptor.
You need to have mechanism to send the data of the class file itself in to the stream before sending the instance.
take a look at the annotateClass and resolveClass methods in ObjectOutputStream and ObjectInputStream