10.3. Externalizable API

An Externalizer is a class that can:
  • Marshall a given object type to a byte array.
  • Unmarshall the contents of a byte array into an instance of the object type.
Externalizers are used by Red Hat JBoss Data Grid and allow users to specify how their object types are serialized. The marshalling infrastructure used in JBoss Data Grid builds upon JBoss Marshalling and provides efficient payload delivery and allows the stream to be cached. The stream caching allows data to be accessed multiple times, whereas normally a stream can only be read once.
The Externalizable interface uses and extends serialization. This interface is used to control serialization and deserialization in JBoss Data Grid.
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10.3.1. Register the Advanced Externalizer (Declaratively)

After the advanced externalizer is set up, register it for use with Red Hat JBoss Data Grid. This registration is done declaratively (via XML) as follows:

Procedure 10.1. Register the Advanced Externalizer

<infinispan>
    <cache-container>
        <serialization>
            <advanced-externalizer class="Book$BookExternalizer" />
        </serialization>
    </cache-container>
</infinispan>
  1. Add the serialization element to the cache-container element.
  2. Add the advanced-externalizer element, defining the custom Externalizer with the class attribute. Replace the Book$BookExternalizer values as required.
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10.3.2. Custom Externalizer ID Values

Advanced externalizers can be assigned custom IDs if desired. Some ID ranges are reserved for other modules or frameworks and must be avoided:

Table 10.1. Reserved Externalizer ID Ranges

ID Range Reserved For
1000-1099 The Infinispan Tree Module
1100-1199 Red Hat JBoss Data Grid Server modules
1200-1299 Hibernate Infinispan Second Level Cache
1300-1399 JBoss Data Grid Lucene Directory
1400-1499 Hibernate OGM
1500-1599 Hibernate Search
1600-1699 Infinispan Query Module
1700-1799 Infinispan Remote Query Module
1800-1849 JBoss Data Grid Scripting Module
1850-1899 JBoss Data Grid Server Event Logger Module
1900-1999 JBoss Data Grid Remote Store
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10.3.2.1. Customize the Externalizer ID (Declaratively)

Customize the advanced externalizer ID declaratively (via XML) as follows:

Procedure 10.2. Customizing the Externalizer ID (Declaratively)

<infinispan>
    <cache-container>
        <serialization>
            <advanced-externalizer id="123"
                                   class="Book$BookExternalizer"/>
        </serialization>    
    </global>
</infinispan>
  1. Add the serialization element to the cache-container element.
  2. Add the advanced-externalizer element to add information about the new advanced externalizer.
  3. Define the externalizer ID using the id attribute. Ensure that the selected ID is not from the range of IDs reserved for other modules.
  4. Define the externalizer class using the class attribute. Replace the Book$BookExternalizer values as required.
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