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