Plugins : Level 1 Cache

DataNucleus is developed as a plugin-driven framework and one of the components that is pluggable is the Level 1 caching of objects (between PersistenceManagers for the same PersistenceManagerFactory). The Cache guide (JDO or JPA) defines three Level 1 caches but is a plugin point so that you can easily add your own variant and have it usable within your DataNucleus usage.

DataNucleus is able to support third party Level 1 Cache products. There are DataNucleus-provided plugins for weak and soft referenced caches. You can extend DataNucleus's capabilities using the plugin extension org.datanucleus.cache_level1.

Plugin extension-point Key Description Location
org.datanucleus.cache_level1 weak Weak referenced cache (default) datanucleus-core
org.datanucleus.cache_level1 soft Soft referenced cache datanucleus-core
org.datanucleus.cache_level1 hard Hard-referenced cache (HashMap) datanucleus-core

The following sections describe how to create your own Level 1 cache plugin for DataNucleus.

Interface

If you have your own Level1 cache you can easily use it with DataNucleus. DataNucleus defines a Level1Cache interface and you need to implement this. 

package org.datanucleus.cache;

public interface Level1Cache extends Map
{
}

So you need to create a class, MyLevel1Cache for example, that implements this interface (i.e that implements java.util.Map).


Plugin Specification

Once you have this implementation you then need to make the class available as a DataNucleus plugin. You do this by putting a file plugin.xml in your JAR at the root of the CLASSPATH. The file plugin.xml will look like this 

<?xml version="1.0"?>
<plugin id="mydomain.mycache" name="DataNucleus plug-ins" provider-name="My Company">
    <extension point="org.datanucleus.cache_level1">
	    <cache name="MyCache" class-name="mydomain.MyLevel1Cache"/>
    </extension>
</plugin>

Note that you also require a MANIFEST.MF file as per the Plugins Guide.

Plugin Usage

The only thing remaining is to use your L1 Cache plugin. To do this you specify the persistence property datanucleus.cache.level1.type as MyCache (the "name" in plugin.xml).