How to cache *any* object type to memory/disk in java?

Question

Is there a generic way to cache any type of object (be in a java class, or a word document etc.) to memory or disk?

Is simply serializing the object, and retaining the file extension (if it has one) enough to rebuild the object?

Answer 1

Not sure what you mean by "or a word document". Serialization can be used for disk caching, not sure what the purpose of using it in memory would be since it would probably be far faster to simply keep the original object.

A more robust solution might be ehcache it can manage the size of the cache as well as moving it between memory and disk.

Answer 2

You seems to be using the word Object to describe 2 different things.

If your object is a Java object then having that object implement the Serializable is enough if you then use the java methods to serialize/de-serialize the object.

If you want to cache arbitrary data from the filesystem, the best way is to read it in an byte array(Or ArrayList). Then you can just write the array back to the disk or where you want it.

Answer 3

If you're talking about the inbuilt Java serialization, then you wouldn't even need to retain the file extension. The serialized form has enough information such that the deserialization process will produce an identical object without any additional help. I suppose that depending on how your code is structured, though, you might need to store some metadata for your own benefit so that you know what to cast the resulting Object as.

Note that Java serialization doesn't seem to fit your requirements, though - it cannot serialize any type of object, only those that implement Serializable. Perhaps you need to think a little more about what you mean by "simply serializing the object", since that's the rub.

Answer 4

No.

There is a class of objects which cannot be deserialized in a meaningful way. Think of an open network connection which is in the middle of transferring a file. You can not store that to disk, close your app, open your app, deserialize that connection and expect that it "just continues".

Java has an interface Serializable which indicates that an object can be serialized. It's up to you to ensure that is indeed possible. Typically an object is Serializable if all the data it holds is Serializable, or that data which is not Serializable is marked transient.

This is not to say that you could not, theoretically, dump the memory contents to a file as a byte stream, and read it back again later. You could build something like that I suppose. But to expect that it works is a different thing altogether.

In short, it is not possible to serialize any type. However, there is a generic way to serialize Java objects which are marked to be Serializable.

Answer 5

If you're wondering about the cross platform (disk or memory) persistence part of the question, look at Java's Preferences class.

Answer 6

You cannot serialize any object in Java. Moreover, Java uses shallow copying(or is it called something else) for serialization, so if you want to seialize something like a HashMap, it might not save your data.

Answer 7

Is this for the web or for the desktop?