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Custom Serialization

Hazelcast lets you plug in a custom serializer for serializing your objects. You can use StreamSerializer and ByteArraySerializer interfaces for this purpose.

Implementing StreamSerializer

You can use a stream to serialize and deserialize data by using StreamSerializer. This is a good option for your own implementations. It can also be adapted to external serialization libraries like Kryo, JSON and protocol buffers.

StreamSerializer Example Code 1

First, let’s create a simple object.

public class EmployeeSS {
    private String surname;
    private String name;

    public EmployeeSS( String surname ) {
        this.surname = surname;
    }

    public String getSurname() {
        return surname;
    }
    public String getName() {
        return name;
    }
}

Now, let’s implement StreamSerializer for Employee class.

public class EmployeeStreamSerializer
        implements StreamSerializer<EmployeeSS> {

    @Override
    public int getTypeId () {
        return 1;
    }

    @Override
    public void write( ObjectDataOutput out, EmployeeSS employee )
            throws IOException {
        out.writeString(employee.getSurname());
    }

    @Override
    public EmployeeSS read( ObjectDataInput in )
            throws IOException {
        String surname = in.readString();
        return new EmployeeSS(surname);
    }

    @Override
    public void destroy () {
    }
}

In practice, classes may have many fields. Just make sure the fields are read in the same order as they are written. The type ID must be unique and greater than or equal to 1. Uniqueness of the type ID enables Hazelcast to determine which serializer is used during deserialization.

As the last step, let’s register the EmployeeStreamSerializer in the configuration file hazelcast.xml/yaml, as shown below.

  • XML

  • YAML

<hazelcast>
    ...
    <serialization>
        <serializers>
            <serializer type-class="EmployeeSS" class-name="EmployeeStreamSerializer" />
        </serializers>
    </serialization>
    ...
</hazelcast>
hazelcast:
  serialization:
    serializers:
      - type-class: EmployeeSS
        class-name: EmployeeStreamSerializer
StreamSerializer cannot be created for well-known types, such as Long and String and primitive arrays. Hazelcast already registers these types.

StreamSerializer Example Code 2

Let’s take a look at another example implementing StreamSerializer.

public class Foo {
    private String foo;

    public String getFoo() {
        return foo;
    }

    public void setFoo( String foo ) {
        this.foo = foo;
    }
}

Assume that our custom serialization serializes Foo into XML. First you need to implement a com.hazelcast.nio.serialization.StreamSerializer. A very simple one that uses XMLEncoder and XMLDecoder could look like the following:

public class FooXmlSerializer implements StreamSerializer<Foo> {

    @Override
    public int getTypeId() {
        return 10;
    }

    public void write( ObjectDataOutput out, Foo object ) throws IOException {
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        XMLEncoder encoder = new XMLEncoder( bos );
        encoder.writeObject( object );
        encoder.close();
        out.write( bos.toByteArray() );
    }

    public Foo read( ObjectDataInput in ) throws IOException {
        InputStream inputStream = (InputStream) in;
        XMLDecoder decoder = new XMLDecoder( inputStream );
        return (Foo) decoder.readObject();
    }

    public void destroy() {
    }
}

Configuring StreamSerializer

Note that typeId must be unique because Hazelcast uses it to look up the StreamSerializer while it deserializes the object. The last required step is to register the StreamSerializer in your Hazelcast configuration. Below are the programmatic and declarative configurations for this step.

SerializerConfig sc = new SerializerConfig()
    .setImplementation(new FooXmlSerializer())
    .setTypeClass(Foo.class);
Config config = new Config();
config.getSerializationConfig().addSerializerConfig(sc);
  • XML

  • YAML

<hazelcast>
    <serialization>
        <serializers>
            <serializer type-class="com.www.Foo" class-name="com.www.FooXmlSerializer" />
        </serializers>
    </serialization>
    ...
</hazelcast>
hazelcast:
  serialization:
    serializers:
      - type-class: com.www.Foo
        class-name: com.www.FooXmlSerializer

From now on, this Hazelcast example will use FooXmlSerializer to serialize Foo objects. In this way, you can write an adapter (StreamSerializer) for any Serialization framework and plug it into Hazelcast.

See the Serialization Configuration Wrap-Up section for a full description of Hazelcast Serialization configuration elements.

Implementing ByteArraySerializer

ByteArraySerializer exposes the raw ByteArray used internally by Hazelcast. It is a good option if the serialization library you are using deals with ByteArrays instead of streams.

Let’s implement ByteArraySerializer for the Employee class mentioned in Implementing StreamSerializer.

public class EmployeeByteArraySerializer
        implements ByteArraySerializer<EmployeeSS> {

    @Override
    public void destroy () {
    }

    @Override
    public int getTypeId () {
        return 1;
    }

    @Override
    public byte[] write( EmployeeSS object )
            throws IOException {
        return object.getName().getBytes();
    }

    @Override
    public EmployeeSS read( byte[] buffer )
            throws IOException {
        String surname = new String( buffer );
        return new EmployeeSS( surname );
    }
}

Configuring ByteArraySerializer

As usual, let’s register the EmployeeByteArraySerializer in the configuration file hazelcast.xml/yaml, as shown below.

  • XML

  • YAML

<hazelcast>
    ...
    <serialization>
        <serializers>
            <serializer type-class="Employee">EmployeeByteArraySerializer</serializer>
        </serializers>
    </serialization>
    ...
</hazelcast>
hazelcast:
  serialization:
    serializers:
      - type-class: Employee
        class-name: EmployeeByteArraySerializer
See the Serialization Configuration Wrap-Up section for a full description of Hazelcast Serialization configuration elements.