Implementing in-memory compression for objects in

Question

We have this use case where we would like to compress and store objects (in-memory) and decompress them as and when required.

The data we want to compress is quite varied, from float vectors to strings to dates.

Can someone suggest any good compression technique to do this ?

We are looking at ease of compression and speed of decompression as the most important factors.

Thanks.

Answer 1

If you want to compress instances of MyObject you could have it implement Serializable and then stream the objects into a compressed byte array, like so:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
GZIPOutputStream gzipOut = new GZIPOutputStream(baos);
ObjectOutputStream objectOut = new ObjectOutputStream(gzipOut);
objectOut.writeObject(myObj1);
objectOut.writeObject(myObj2);
objectOut.close();
byte[] bytes = baos.toByteArray();

Then to uncompress your byte[] back into the objects:

ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
GZIPInputStream gzipIn = new GZIPInputStream(bais);
ObjectInputStream objectIn = new ObjectInputStream(gzipIn);
MyObject myObj1 = (MyObject) objectIn.readObject();
MyObject myObj2 = (MyObject) objectIn.readObject();
objectIn.close();

Answer 2

If you need to compress arbitrary objects, a possible approach is to serialize the object into a byte array, and then use e.g. the DEFLATE algorithm (the one used by GZIP) to compress it. When you need the object, you can decompress and deserialize it. Not sure about how efficient this would be, but it will be completely general.