<form:select> fails to bind to java.util.Set property

[jespey]

I have a form that uses form:form tags. In particular I bind a multi-select box to a java.util.Set property. It works fine to save a new record, but when I attempt to render an existing element, I get an error message about converting. I'm using @InitBinder and a custom property editor, as listed in the below @Controller code:

@Controller @RequestMapping("/admin")
public class LiftTypeFormController {
    Log log = LogFactory.getLog(getClass());
    private LiftWorkoutDao liftWorkoutDao;
    private MuscleGroupEditor muscleGroupEditor;
    
    
    
    @RequestMapping(value = "/liftType/{liftTypeId}", method = RequestMethod.GET)
    public String editLiftType(@PathVariable Integer liftTypeId, Model model) {
    	model.addAttribute(liftWorkoutDao.findLiftTypeById(liftTypeId));
    	return "liftType";
    }
    
    @InitBinder("liftType") 
    protected void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(Integer.class, null, new CustomNumberEditor(Integer.class, new DecimalFormat(), true));
        binder.registerCustomEditor(MuscleGroup.class, muscleGroupEditor);

Here is the relevant JSP fragment:

                <td>
                            	<form:select path="muscleGroups" size="15" multiple="true" items="${childlessMuscleGroups}"
                            		itemValue="muscleGroupId" itemLabel="name"/>
                                <font color="red"><form:errors path="muscleGroups"/></font>                                    
                            </td>

If I take it down to just <form:select path="muscleGroups"/> and nothing else, I still get the following error (but only on edit, not on add new):

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from 'com.espey.common.dto.workout.lift.MuscleGroup' to 'java.lang.String'
	org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:181)
	org.springframework.core.convert.support.CollectionToStringConverter.convert(CollectionToStringConverter.java:65)
	org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:36)
	org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:184)
	org.springframework.validation.AbstractPropertyBindingResult.formatFieldValue(AbstractPropertyBindingResult.java:124)
	org.springframework.validation.AbstractBindingResult.getFieldValue(AbstractBindingResult.java:227)
	org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:120)
	org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:174)

I can also replace the <form:select> tag with old school <spring:bind> and I get the same error. Again, I know the PropertyEditor works since the form works for adding new items, but for some reason it doesn't work on rendering an existing form. I added debugging and can see that the @InitBinder method is invoked prior to rendering the page too. For what it's worth, I've also added a CustomCollection editor and had the exact same result.

If I should be using a different approach like formatting or conversion to do this, can someone please point me in the right direction?

[Enrico Pizzi]

You shouldn't use editors but define a MuscleGroupToStringConverter and register it using Spring's Converter SPI. Read the reference documentation.

[jespey]

Thanks, I had a feeling I should do that but wasn't sure if there was a quick fix for this.