Question

I have a very large object which I wish to serialize. During the process of serialization, it comes to occupy some 130MB of heap as an weblogic.utils.io.UnsyncByteArrayOutputStream. I am using a BufferedOutputStream to speed up writing the data to disk, which reduces the amount of time for which this object is held in memory.

Is it possible to use a buffer to reduce the size of the object in memory though? It would be good if there was a way to serialize it x bytes at a time and write those bytes to disk.

Sample code follows if it is of any use. There’s not much to go on though I don’t think. If it’s the case that there needs to be a complete in-memory copy of the object to be serialised (and therefore no concept of a serialization buffer) then I suppose I am stuck.

    ObjectOutputStream tmpSerFileObjectStream = null;
    OutputStream tmpSerFileStream = null;
    BufferedOutputStream bufferedStream = null;
    try {

        tmpSerFileStream = new FileOutputStream(tmpSerFile);
        bufferedStream = new BufferedOutputStream(tmpSerFileStream);

        tmpSerFileObjectStream = new ObjectOutputStream(bufferedStream);
        tmpSerFileObjectStream.writeObject(siteGroup);
        tmpSerFileObjectStream.flush();

    } catch (InvalidClassException invalidClassEx) {
        throw new SiteGroupRepositoryException(
                "Problem encountered with class being serialised", invalidClassEx);
    } catch (NotSerializableException notSerializableEx) {
        throw new SiteGroupRepositoryException(
                "Object to be serialized does not implement " + Serializable.class,
                notSerializableEx);
    } catch (IOException ioEx) {
        throw new SiteGroupRepositoryException(
                "Problem encountered while writing ser file", ioEx);
    } catch (Exception ex) {
        throw new SiteGroupRepositoryException(
                "Unexpected exception encountered while writing ser file", ex);
    } finally {
        if (tmpSerFileObjectStream != null) {
            try {
                tmpSerFileObjectStream.close();
                if(null!=tmpSerFileStream)tmpSerFileStream.close();
                if(null!=bufferedStream)bufferedStream.close();
            } catch (IOException ioEx) {
                logger.warn("Exception caught on trying to close ser file stream", ioEx);
            }
        }
    }

Answer 1

What is the “siteGroup” object that you’re trying to save? I ask, because it’s unlikely that any one object is 130MB in size, unless it has a ginormous list/array/map/whatever in it — and if that’s the case, the answer would be to persist that data in a database.

But if there’s no monster collection in the object, then the problem is likely that the object tree contains references to a bagillion objects, and the serialization of course does a deep copy (this fact has been used as a shortcut to implement clone() a lot of times), so everything gets cataloged all at once in a top-down fashion.

If that’s the problem, then the solution would be to implement your own serialization scheme where each object gets serialized in a bottom-up fashion, possibly in multiple files, and only references are maintained to other objects, instead of the whole thing. This would allow you to write each object out individually, which would have the effect you’re looking for: smaller memory footprint due to writing the data out in chunks.

However, implementing your own serialization, like implementing a clone() method, is not all that easy. So it’s a cost/benefit thing.