How to convert string into existing instance in Spring MVC?

Here is the scenario:

1. Controller preperes list of available brandings (CrudRepository, Database). List<PortalBranding>
2. This list goes to View as ModelMap attribute.

3. View list them using form:select

     <form:select path="branding">
           <form:option value="-" label="--Please Select"/>
           <form:options items="${brandingList}" itemValue="id" itemLabel="name"/>
     </form:select>
   

4. When selected, by default it tries to send value as String, which I want to convert to PortalBranding object. So I added @InitBinder method where I can register my custom editor:

   public class PortalBrandingEditor extends PropertyEditorSupport { ... }
   

   But if I want it to have access to some service which loads object by id, I would like Spring to create instance based on some annotation (I would place some @Autowired field inside this Editor). Is that good way? What annonation would be best for it? Looking forward for some suggestions.

What you need is Spring's ConversionService. Here's the reference: http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#core-convert

Simply implement Converter similar to this:

public class StringToPortalBrandingConverter implements Converter<String, PortalBranding> {

    @Inject // or @Autowire
    SomeService someService; // Some service or other dependency you need.

    @Override
    public PortalBranding convert(String source) {
        // Do your conversion from 'source' to 'PortalBranding' here.
        // You can make use of your injected 'someService' as well.
        ...
        return portalBranding;
    }
}

Then, you just need to tell Spring about your custom converter:

<mvc:annotation-driven conversion-service="conversionService"/>

<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <set>
            <bean class="yourpackage.StringToPortalBrandingConverter"/>
        </set>
    </property>
</bean>

That's all there is to it.