Kryo and compression, how does it work?

[mean mole]

Hello,

I have read the Github manual page about compression but I can't figure how to make use of it properly.

Here's an example snippet from my app that works perfectly fine:

// serialize and write object to disk:

val writeFile = combinedColladaModel.serializedFile
val output = Output(FileOutputStream(writeFile))
modelSerializer.writeObject(output, sm)
output.close()

...

// later read the serialized file back as object:

val input = Input(FileInputStream(fileName!!))
val modelData: SerializedModel = k.readObject(input, SerializedModel::class.java)
input.close()

Now if I change the code to be like this:

// serialize and write object to disk: (OK):

val writeFile = combinedColladaModel.serializedFile
val output = Output(DeflaterOutputStream(FileOutputStream(writeFile)))
modelSerializer.writeObject(output, sm)
output.close()

...

// later read the serialized file back as object (CRASH):

val input = Input(DeflaterInputStream(FileInputStream(fileName!!)))
val modelData: SerializedModel = k.readObject(input, SerializedModel::class.java)
input.close()

The object gets compressed and serialized to disk (the file on the disk now has significantly smaller size) but when I try to read it back to my application from the disk, as shown in the code above, I get "KryoException: Buffer underflow".

Is this the correct way to use the compression? Are there any code examples online showing how object compression, serialization and deserialization can be done with Kryo?

Thanks! 

[Thomas Heigl]

Hi,

I think you have to use `InflaterInputStream` instead of `DeflaterInputStream` when reading the compressed file. This would be a good addition to the Readme.

I have never used compression with `DeflaterOutputStream`. What I usually do is compress the byte[] that Kryo produces and decompress it again before deserialization. I strongly recommend using

https://github.com/lz4/lz4-java for this if you want optimal speed and compressed size.

Thomas

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[mean mole]

Hey,

Thanks for pointing that out! Deflater / Inflater, makes sense I guess :) I don't have previous experience with these compression tools, but the compression works now as it should!

I will also check out the lz4-java later. 

Have a nice day!