Thanks @Pelit_Mamani for some suggestions. I did try to implement a converter and set it in mongo mapping converter and it seems to work. It works even when the object is embedded in other object.
<mongo:mapping-converter id="mappingConverter" base-package="com.mytest.domain" db-factory-ref="mongoDbFactory" disable-validation="true">
<mongo:custom-converters>
<mongo:converter>
<bean class="com.mytest.repo.converter.MyReadConverter" />
</mongo:converter>
</mongo:custom-converters>
</mongo:mapping-converter>
And the converter class:
public class MyReadConverter implements Converter<DBObject, MyObject>