Prevent Dozer from triggering Hibernate lazy loading

The only generic solution I have found for managing this (after looking into Custom Converters, Event Listeners & Proxy Resolvers) is by implementing a Custom Field Mapper. I found this functionality tucked away in the Dozer API (I don't believe it is documented in the User Guide).

A simple example is as follows;

public class MyCustomFieldMapper implements CustomFieldMapper 
{
    public boolean mapField(Object source, Object destination, Object sourceFieldValue, ClassMap classMap, FieldMap fieldMapping) 
    {       
        // Check if field is a Hibernate collection proxy
        if (!(sourceFieldValue instanceof AbstractPersistentCollection)) {
            // Allow dozer to map as normal
            return false;
        }

        // Check if field is already initialized
        if (((AbstractPersistentCollection) sourceFieldValue).wasInitialized()) {
            // Allow dozer to map as normal
            return false;
        }

        // Set destination to null, and tell dozer that the field is mapped
        destination = null;
        return true;
    }   
}

This will return any non-initialized PersistentSet objects as null. I do this so that when they are passed to the client I can differentiate between a NULL (non-loaded) collection and an empty collection. This allows me to define generic behaviour in the client to either use the pre-loaded set, or make another service call to retrieve the set (if required). Additionally, if you decide to eagerly load any collections within the service layer then they will be mapped as usual.

I inject the custom field mapper using spring:

<bean id="dozerMapper" class="org.dozer.DozerBeanMapper" lazy-init="false">
    <property name="mappingFiles">
        ...
    </property>
    <property name="customFieldMapper" ref="dozerCustomFieldMapper" />
</bean>
<bean id="dozerCustomFieldMapper" class="my.project.MyCustomFieldMapper" />

I hope this helps anyone searching for a solution for this, as I failed to find any examples when searching the Internet.

A variation on the popular version above, makes sure to catch both PersistentBags, PersistentSets, you name it...

public class LazyLoadSensitiveMapper implements CustomFieldMapper {

public boolean mapField(Object source, Object destination, Object sourceFieldValue, ClassMap classMap, FieldMap fieldMapping) {
    //if field is initialized, Dozer will continue mapping

    // Check if field is derived from Persistent Collection
    if (!(sourceFieldValue instanceof AbstractPersistentCollection)) {
        // Allow dozer to map as normal
        return false;
    }

    // Check if field is already initialized
    if (((AbstractPersistentCollection) sourceFieldValue).wasInitialized()) {
        // Allow dozer to map as normal
        return false;
    }

    return true;
}

}