package org.datanucleus;
...
public interface ClassLoaderResolver
{
    /**
     * Class loading method, allowing specification of a primary loader. 
     * This method does not initialize the class
     * @param name Name of the Class to be loaded
     * @param primary the primary ClassLoader to use (or null)
     * @return The Class given the name, using the specified ClassLoader
     * @throws ClassNotResolvedException if the class can't be found in the classpath
     */
    public Class classForName(String name, ClassLoader primary);

    /**
     * Class loading method, allowing specification of a primary loader
     * and whether the class should be initialised or not.
     * @param name Name of the Class to be loaded
     * @param primary the primary ClassLoader to use (or null)
     * @param initialize whether to initialize the class or not.
     * @return The Class given the name, using the specified ClassLoader
     * @throws ClassNotResolvedException if the class can't be found in the classpath
     */
    public Class classForName(String name, ClassLoader primary, boolean initialize);

    /**
     * Class loading method. This method does not initialize the class
     * @param name Name of the Class to be loaded
     * @return The Class given the name, using the specified ClassLoader
     */
    public Class classForName(String name);

    /**
     * Class loading method, allowing for initialisation of the class.
     * @param name Name of the Class to be loaded
     * @param initialize whether to initialize the class or not.
     * @return The Class given the name, using the specified ClassLoader
     */
    public Class classForName(String name, boolean initialize);

    /**
     * Method to test whether the type represented by the specified class_2 
     * parameter can be converted to the type represented by class_name_1 parameter.
     * @param class_name_1 Class name
     * @param class_2 Class to compare against
     * @return Whether they are assignable
     */
    public boolean isAssignableFrom(String class_name_1, Class class_2);

    /**
     * Method to test whether the type represented by the specified class_name_2 
     * parameter can be converted to the type represented by class_1 parameter.
     * @param class_1 First class
     * @param class_name_2 Class name to compare against
     * @return Whether they are assignable
     */
    public boolean isAssignableFrom(Class class_1, String class_name_2);

    /**
     * Method to test whether the type represented by the specified class_name_2 
     * parameter can be converted to the type represented by class_name_1 parameter.
     * @param class_name_1 Class name
     * @param class_name_2 Class name to compare against
     * @return Whether they are assignable
     */
    public boolean isAssignableFrom(String class_name_1, String class_name_2);
    
    /**
     * ClassLoader registered to load classes created at runtime. One ClassLoader can
     * be registered, and if one ClassLoader is already registered, the registered ClassLoader
     * is replaced by <code>loader</code>.
     * @param loader The ClassLoader in which classes are defined
     */
    public void registerClassLoader(ClassLoader loader);

    /**
     * ClassLoader registered by users to load classes. One ClassLoader can
     * be registered, and if one ClassLoader is already registered, the registered ClassLoader
     * is replaced by <code>loader</code>.
     * @param loader The ClassLoader in which classes are loaded
     */
    public void registerUserClassLoader(ClassLoader loader);

    /**
     * Finds all the resources with the given name.
     * @param resourceName the resource name. If <code>resourceName</code> starts with "/", 
     *           remove it before searching.
     * @param primary the primary ClassLoader to use (or null)
     * @return An enumeration of URL objects for the resource. If no resources could be found,
     *           the enumeration will be empty. 
     * Resources that the class loader doesn't have access to will not be in the enumeration.
     * @throws IOException If I/O errors occur
     * @see ClassLoader#getResources(java.lang.String)
     */
    public Enumeration getResources(String resourceName, ClassLoader primary) throws IOException;
    
    /**
     * Finds the resource with the given name.
     * @param resourceName the path to resource name relative to the classloader root path. 
     *        If <code>resourceName</code> starts with "/", remove it.   
     * @param primary the primary ClassLoader to use (or null)
     * @return A URL object for reading the resource, or null if the resource could not be found or 
     *         the invoker doesn't have adequate privileges to get the resource. 
     * @throws IOException If I/O errors occur
     * @see ClassLoader#getResource(java.lang.String)
     */
    public URL getResource(String resourceName, ClassLoader primary);
    
    /**
     * Sets the primary classloader for the current thread.
     * The primary should be kept in a ThreadLocal variable.
     * @param primary the primary classloader
     */
    void setPrimary(ClassLoader primary);

    /**
     * Unsets the primary classloader for the current thread
     */
    void unsetPrimary();
    
}

package mydomain;

import org.datanucleus.ClassLoaderResolver;

public class MyClassLoaderResolver implements ClassLoaderResolver
{
    /**
     * Constructor for PersistenceManager cases.
     * @param pmLoader Loader from PM initialisation time.
     */
    public MyClassLoaderResolver(ClassLoader pmLoader)
    {
         ...
    }

    .. (implement the interface)
}

<?xml version="1.0"?>
<plugin id="mydomain" name="DataNucleus plug-ins" provider-name="My Company">
    <extension point="org.datanucleus.classloader_resolver">
        <class-loader-resolver name="myloader" class-name="mydomain.MyClassLoaderResolver"/>
    </extension>
</plugin>