How can I use Kryo to serialize an object and deserialize it again?

Question

How can I use Kryo to serialize an object and deserialize it again? I am working in Kryo 2.23.0

Solution 1

Kryo's syntax is relatively similar to java serialisation. A kryo object is created as well as an output/input and one of kryos methods is used to perform the serialisation/deserialisation

• kryo.writeClassAndObject(output, object); //for if the concrete class isn't known (can be null)
• kryo.writeObjectOrNull(output, someObject); //if the object could be null
• kryo.writeObject(output, someObject); //can't be null and concrete class is known

Each of the writes is paired with a read

• SomeClass object = (SomeClass)kryo.readClassAndObject(input);
• SomeClass someObject = kryo.readObjectOrNull(input, SomeClass.class);
• SomeClass someObject = kryo.readObject(input, SomeClass.class);

The following is an example using writeClassAndObject that serialises a Vector3d to a file and back again.

public class KryoTest {
    public static void main(String[] args){

        Vector3d someObject=new Vector3d(1,2,3);

        //serialise object

        //try-with-resources used to autoclose resources
        try (Output output = new Output(new FileOutputStream("KryoTest.ser"))) {
            Kryo kryo=new Kryo();
            kryo.writeClassAndObject(output, someObject);
        } catch (FileNotFoundException ex) {
            Logger.getLogger(KryTest.class.getName()).log(Level.SEVERE, null, ex);
        }

        //deserialise object

        Vector3d retrievedObject=null;

        try (Input input = new Input( new FileInputStream("KryoTest.ser"))){
            Kryo kryo=new Kryo();
            retrievedObject=(Vector3d)kryo.readClassAndObject(input);
        } catch (FileNotFoundException ex) {
            Logger.getLogger(KryTest.class.getName()).log(Level.SEVERE, null, ex);
        }

        System.out.println("Retrieved from file: " + retrievedObject.toString());
    }
}

All the up to date documentation has moved to github now; https://github.com/EsotericSoftware/kryo#quickstart

Solution 2

A simple version:

Kryo kryo = new Kryo();
// #### Store to disk...
Output output = new Output(new FileOutputStream("file.bin"));
SomeClass someObject = ...
kryo.writeObject(output, someObject);
output.close();
// ### Restore from disk...
Input input = new Input(new FileInputStream("file.bin"));
SomeClass someObject = kryo.readObject(input, SomeClass.class);
input.close();

Comments

[Mike Rylander]

It should be noted that this example requires Java 7.