How to create and config an inner builder class with spring

I am trying to springify the following code snippet:

MongoClient mongoClient = new MongoClient("127.0.0.1", 27017);
DB db = mongoClient.getDB("jcr");
DocumentNodeStore ns = new DocumentMK.Builder().setMongoDB(db)
                .getNodeStore();
Repository repo = new Jcr(new Oak(ns)).createRepository();

taken from Oak website : http://ift.tt/1GlTtVJ

The problem line is:

DocumentNodeStore ns = new DocumentMK.Builder().setMongoDB(db)
                .getNodeStore();

Here is how I have configured it within the xml:

<bean id="builder" class="org.apache.jackrabbit.oak.plugins.document.DocumentMK$Builder">   
        </bean>

<bean factory-bean="builder" factory-method="setMongoDB" >
       <constructor-arg name="db" value="#{mongoDbTags.getDb()}"/>
</bean>

I have configured a SimpleMongoDbFactory and obtaining the db to be injected into the builder bean calling the setMethod via factory method.

Please note this does not exist as an attribute under the builder Class but the method does exist.

here is my config file:

    <bean id="mongo" class="com.mongodb.MongoClient">
        <constructor-arg name="host" value="localhost" />
        <constructor-arg name="port" value="27017" />
    </bean>
        <bean id="mongoDbTags" class="org.springframework.data.mongodb.core.SimpleMongoDbFactory">
            <constructor-arg name="mongo" ref="mongo" />
            <constructor-arg name="databaseName" value="jcr111" />
        </bean>
    <bean id="builder" class="org.apache.jackrabbit.oak.plugins.document.DocumentMK$Builder">   
    </bean>

        <bean factory-bean="builder" factory-method="setMongoDB" >
             <constructor-arg name="db" value="#{mongoDbTags.getDb()}"/>
          </bean>
    <bean id="documentMK" class="org.apache.jackrabbit.oak.plugins.document.DocumentMK">
    <constructor-arg name="builder" ref="builder" />
    </bean>

    <bean id="oak" class="org.apache.jackrabbit.oak.Oak">
        <constructor-arg name="store" value="#{builder.getNodeStore()}" />
    </bean>

    <bean id="jcr" class="org.apache.jackrabbit.oak.jcr.Jcr">
        <constructor-arg name="oak" ref="oak" />
    </bean>
        <bean id="jcrSessionFactory"
            class="org.springframework.extensions.jcr.JcrSessionFactory">
            <property name="repository"  value="#{jcr.createRepository()}" />
            <property name="credentials">
  <bean class="javax.jcr.SimpleCredentials">
                    <constructor-arg index="0" value="admin" />
                    <constructor-arg index="1" value="admin" />
                </bean>
            </property>
        </bean>

        <bean id="jcrTemplate" class="org.springframework.extensions.jcr.JcrTemplate">
            <property name="sessionFactory" ref="jcrSessionFactory" />
            <property name="allowCreate" value="true" />
        </bean>