Serialization is the process of saving an object in a persistent form, e.g., on the harddisk as a bytestream. Deserialization is the process in the opposite direction, creating an object from a persistently saved data structure. In Java, an object can be serialized if it imports the interface.

Members of an object that are not supposed to be serialized, need to be prefixed with the keyword transient.

In the following you'll find some Java code snippets for serializing and deserializing a J48 classifier. Of course, serialization is not limited to classifiers. Most schemes in Weka, like clusterers and filters, are also serializable.


Here we create a J48 classifier cls, train it with a dataset /some/where/data.arff, and save the built model to a file /some/where/j48.model.

 // create J48
 Classifier cls = new J48();

 // train
 Instances inst = new Instances(
                    new BufferedReader(
                      new FileReader("/some/where/data.arff")));
 inst.setClassIndex(inst.numAttributes() - 1);

 // serialize model
 ObjectOutputStream oos = new ObjectOutputStream(
                            new FileOutputStream("/some/where/j48.model"));

If you use the SerializationHelper class, then this shrinks to:

 // serialize model
 weka.core.SerializationHelper.write("/some/where/j48.model", cls);


Here the previously saved model is deserialized as cls and again available for classification.

 // deserialize model
 ObjectInputStream ois = new ObjectInputStream(
                           new FileInputStream("/some/where/j48.model"));
 Classifier cls = (Classifier) ois.readObject();

Or, with the SerializationHelper class:

 // deserialize model
 Classifier cls = (Classifier)"/some/where/j48.model");

Serialization in Weka

The Explorer serializes the classifier and the training header together. This makes it easy to test whether a dataset is compatible with the dataset the classifier was trained with. The commandline option -d of the developer version stores the training header as well.

In order to read serialized models that contain the header information as well, you can use the readAll method of the weka.core.SerializationHelper. For serializing models with their datasets, use writeAll.

See also