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.
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
).
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> 
