Oracle Coherence has a component called CacheStore that can be used to integrate "any" external data source with the Coherence Grid. Typically this external data source is a relational database, but it can be a Directory Server and in fact other Coherence data grid. CacheStore is also used to implement multi-cluster data replication strategies using Coherence. To demonstrate this very fact I wrote the following implementation to integrate JavaSpace as my external data source for the Coherence Grid.

Challenges:

• JavaSpace works on a Collection, Coherence NamedCache is a Map
• Data Access in NamedCache is by Key (Or a Extractor Query), In Java Space its a template Query

So how would I do it?

Create a Coherence Cache Config

<!DOCTYPE cache-config SYSTEM "cache-config.dtd">
<cache-config>
    <caching-scheme-mapping>
        <cache-mapping>
            <cache-name>SpaceCache</cache-name>
            <scheme-name>distributed-scheme</scheme-name>
        </cache-mapping>       
    </caching-scheme-mapping>
    <caching-schemes>
        <distributed-scheme>
            <scheme-name>distributed-scheme</scheme-name>
            <service-name>DistributedCache</service-name>
            <backing-map-scheme>
                <read-write-backing-map-scheme>
                    <scheme-ref>rw-bm</scheme-ref>
                </read-write-backing-map-scheme>
            </backing-map-scheme>
            <autostart>true</autostart>           
        </distributed-scheme>
       
        <read-write-backing-map-scheme>
            <scheme-name>rw-bm</scheme-name>
            <internal-cache-scheme>
                <local-scheme></local-scheme>
            </internal-cache-scheme>
            <cachestore-scheme>
                <class-scheme>
                    <class-name>SpaceCacheStore</class-name>
                </class-scheme>               
            </cachestore-scheme>
        </read-write-backing-map-scheme>       
    </caching-schemes>
</cache-config>

Create a Jini Entry Object:

public class MessageEntry implements Entry {

    public Binary oKey;
    public Binary oValue;
   
    public MessageEntry() {
    }
   
    public MessageEntry (Binary oKey, Binary oValue) {
        this.oKey = oKey;
        this.oValue = oValue;
    }
   
    public String toString () {
        return "oKey: " + ExternalizableHelper.fromBinary(oKey) +
               ": oValue: " + ExternalizableHelper.fromBinary (oValue);
    }
}

Create a Coherence Cache Store:

public class SpaceCacheStore implements CacheStore {

    private boolean isInitialized;
    private JavaSpace space;

    private void init() {
    }