How to convert string into existing instance in Spring MVC?

Question

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.

Answer 1

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.

Answer 2

I found working solution for now.

I simply create new PortalBranding in the Editor class, set it's id. So the portal has branding with id which exists. The rest is done by Persistance (Hibernate).

But still looking forward for other solutions :).