Accessing Serialized Files randomly.

Question

I have a problem accessing serailized files randomly. I am using ObjectOutputStream to write objects to a file. I am using the ObjectInputStream to read the objects from the file. Both of these work fine if the order in which i Write objects is the same as the order in which I read Objects. But I need to skip few objects when reading objects from the file. I know API states that the order of writing and reading should be the same. But still is there any way where i can read serailized objects ramdomly form the file.
Please help me with this it is very impritant of the project. We are trying to store tuples in the file. We are going to build an index over these tuples and then read the tuple that we need.
Thankyou,
Nishant

Answer 1

You could wrap the ObjectOutputStream around a ByteArrayOutputStream to first serialize an object to a byte[] and then save that into a RandomAccessFile.
The trick is to be able to tell where in the file each serialized object starts. Possibilities include:
1) If your objects are known to serialize to a fixed size (or if there is a reasonable max size of the serialized object), you could pad each byte[] "record" you write to the file (eg, each object always uses 1K bytes). Then you can easily read back the i'th object byte[] and deserialize it.
2) Design into your RandomAccessFile a "directory" section that keeps track of each stored object and it's starting byte address in the file.
If the file needs to hold an arbitrary # of objects, the directory could support a special entry pointing to a "next" directory section later in the file.
-Brian