Comparing java object trees

Question

Hello.
I was wondering if someone might have some advice or ideas about this seemingly very common problem.
I have two copies of a very large java object tree (original and modified). I need to compare these two trees and figure out whether any data has changed. The brute force way to do this would of course be to implement equals() method for all of my objects, but in my case this would be A LOT of work.
So, I want to find a way to compare the two trees in a generic way.
My first attempt was to serialize both trees into memory and then compare them on the binary level, like this:
     public boolean autoEquals(BaseDomainObject other) {
          try {
               ByteArrayOutputStream thisObjectStream = new ByteArrayOutputStream(500);
               ObjectOutputStream out = new ObjectOutputStream(thisObjectStream);
               out.writeObject(this);
               out.flush();
               out.close();
               ByteArrayOutputStream otherObjectStream = new ByteArrayOutputStream(500);
               out = new ObjectOutputStream(otherObjectStream);
               out.writeObject(other);
               out.flush();
               out.close();
               return thisObjectStream.toString().equals(otherObjectStream.toString());
          catch (Exception e) {
               throw new RuntimeException(e);
     }This actually nearly worked, except for one problem that I do not know how to address - The order of elements in collections of the modified tree might differ from the order of the same collections in the original tree, even if the individual elements are exactly the same. My serialization idea falls apart here.
Can someone think of another way to do this?
Any ideas would be appreciated.

Answer 1

I thought I would follow up with the solution.
The method I described above does work, but in order to make it work I had to find a way to make all elements in all collections appear in the same order. In order to do that, I needed a unique key for each object in the tree, that would be the same in both the original and the modified tree.
In my case that was easy, b/c I get the original version from Hibernate and I make my modified version by copying it (also by serializing the original into memory and then deserializing it into my new "modified" working copy tree), so they both still contain the hibernate oids.
The extra step I needed to do before serializing and comparing was to recurse through both trees (with Introspection) and replace all sets with a TreeSet and all lists with my own implementation of a sorted list.
Now I can compare any tree of domain objects that extend from BaseDomainObject (they all do) by simply writing
domainObjectTree1.autoEquals(domainObjectTree2, new String[] {"terminatorProperty1", "terminatorProperty2", ...})
Terminator properties are basically properties which I set to null before running my comparison. This allows me to "cut off" branches of the tree that I don't want to be compared.