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[DOCS-590]: Serialization content improvements (#862)
* Serialization content improvements * Gathering low-lighted options under a parent title in ToC.
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docs/modules/serialization/pages/implementing-identifieddataserializable.adoc
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| = IdentifiedDataSerializable | ||
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| For a faster serialization of objects, avoiding reflection and long class names, | ||
| Hazelcast recommends you to implement `com.hazelcast.nio.serialization.IdentifiedDataSerializable`. | ||
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| `IdentifiedDataSerializable` uses a factory to create a class instance (with reflection) and | ||
| it is fast during deserialization, which requires new instance creations. | ||
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| == getClassId and getFactoryId Methods | ||
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| `IdentifiedDataSerializable` extends xref:implementing-dataserializable.adoc[`DataSerializable`] and introduces the following methods: | ||
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| * `int getClassId();` | ||
| * `int getFactoryId();` | ||
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| `IdentifiedDataSerializable` uses `getClassId()` instead of class name and it uses | ||
| `getFactoryId()` to load the class when given the id. To complete the implementation, | ||
| you should also implement `com.hazelcast.nio.serialization.DataSerializableFactory` and | ||
| register it into `SerializationConfig`, which can be accessed from `Config.getSerializationConfig()`. | ||
| Factory's responsibility is to return an instance of the right `IdentifiedDataSerializable` object, given the id. | ||
| This is currently the most efficient way of Serialization that Hazelcast supports off the shelf. | ||
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| == Implementing IdentifiedDataSerializable | ||
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| Let's take a look at the following example code and configuration to see `IdentifiedDataSerializable` in action. | ||
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| [source,java] | ||
| ---- | ||
| public class Employee | ||
| implements IdentifiedDataSerializable { | ||
| private String surname; | ||
| public Employee() {} | ||
| public Employee( String surname ) { | ||
| this.surname = surname; | ||
| } | ||
| @Override | ||
| public void readData( ObjectDataInput in ) | ||
| throws IOException { | ||
| this.surname = in.readString(); | ||
| } | ||
| @Override | ||
| public void writeData( ObjectDataOutput out ) | ||
| throws IOException { | ||
| out.writeString( surname ); | ||
| } | ||
| @Override | ||
| public int getFactoryId() { | ||
| return EmployeeDataSerializableFactory.FACTORY_ID; | ||
| } | ||
| @Override | ||
| public int getClassId() { | ||
| return EmployeeDataSerializableFactory.EMPLOYEE_TYPE; | ||
| } | ||
| @Override | ||
| public String toString() { | ||
| return String.format( "Employee(surname=%s)", surname ); | ||
| } | ||
| } | ||
| ---- | ||
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| The methods `getClassId` and `getFactoryId` return a unique positive number within | ||
| the `EmployeeDataSerializableFactory`. | ||
| Now, let's create an instance of this `EmployeeDataSerializableFactory`. | ||
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| [source,java] | ||
| ---- | ||
| public class EmployeeDataSerializableFactory | ||
| implements DataSerializableFactory{ | ||
| public static final int FACTORY_ID = 1; | ||
| public static final int EMPLOYEE_TYPE = 1; | ||
| @Override | ||
| public IdentifiedDataSerializable create(int typeId) { | ||
| if ( typeId == EMPLOYEE_TYPE ) { | ||
| return new Employee(); | ||
| } else { | ||
| return null; | ||
| } | ||
| } | ||
| } | ||
| ---- | ||
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| The only method you should implement is `create`, as seen in the above example. | ||
| It is recommended that you use a `switch-case` statement instead of | ||
| multiple `if-else` blocks if you have a lot of subclasses. | ||
| Hazelcast throws an exception if null is returned for `typeId`. | ||
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| [[register]] | ||
| == Registering EmployeeDataSerializableFactory | ||
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| As the last step, you need to register `EmployeeDataSerializableFactory` declaratively | ||
| (declare in the configuration file `hazelcast.xml/yaml`) as shown below. | ||
| Note that `factory-id` has the same value of `FACTORY_ID` in the above code. | ||
| This is crucial to enable Hazelcast to find the correct factory. | ||
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| [tabs] | ||
| ==== | ||
| XML:: | ||
| + | ||
| -- | ||
| [source,xml] | ||
| ---- | ||
| <hazelcast> | ||
| ... | ||
| <serialization> | ||
| <data-serializable-factories> | ||
| <data-serializable-factory factory-id="1"> | ||
| com.company.package.EmployeeDataSerializableFactory | ||
| </data-serializable-factory> | ||
| </data-serializable-factories> | ||
| </serialization> | ||
| ... | ||
| </hazelcast> | ||
| ---- | ||
| -- | ||
| YAML:: | ||
| + | ||
| [source,yaml] | ||
| ---- | ||
| hazelcast: | ||
| serialization: | ||
| data-serializable-factories: | ||
| - factory-id: 1 | ||
| class-name: com.company.package.EmployeeDataSerializableFactory | ||
| ---- | ||
| ==== | ||
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| == Hazelcast Clients | ||
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| When using a client/server deployment, you also need to register the implemented factory on | ||
| the client side. For a Java client, the process is the same as described above to be performed | ||
| in the client configuration, e.g., `hazelcast-client.xml/yaml`. | ||
| For the other Hazelcast clients, see the following for details: | ||
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| * https://github.com/hazelcast/hazelcast-csharp-client#41-identifieddataserializable-serialization[.NET^] | ||
| * https://github.com/hazelcast/hazelcast-cpp-client#41-identifieddataserializable-serialization[C++^] | ||
| * https://github.com/hazelcast/hazelcast-nodejs-client#41-identifieddataserializable-serialization[Node.js^] | ||
| * https://github.com/hazelcast/hazelcast-python-client#41-identifieddataserializable-serialization[Python^] | ||
| * https://github.com/hazelcast/hazelcast-go-client#41-identifieddataserializable-serialization[Go^] |
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