Spring 4 Converters

I'm writing a webserivce using Spring 4. I have a problem with data binding. I've got org.springframework.beans.ConversionNotSupportedException: Failed to convert property value of type 'java.util.ArrayList' to required type 'java.util.Set' for property 'groups'; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [pl.tt.springtpl.models.Group] for property 'groups[0]': no matching editors or conversion strategy found exception. I'm sending an object in json. In service I binding properties of received map to entity. All is ok if the properties are primitive. But If I have a custom pojo I have that exception.

I wrote two classes:

public class ArrayListToSetConverter implements Converter<ArrayList, Set>{

    public Set convert(ArrayList source) {
        Set set = new HashSet();
        set.addAll(source);
        return set;
    }

}

and I'm trying to do it more generic with this class:

public class StringToAbstractEntityConverter implements ConditionalGenericConverter{

    public Set<ConvertiblePair> getConvertibleTypes() {
        ConvertiblePair cp = new ConvertiblePair(String.class, SimpleAbstractEntity.class);
        Set<ConvertiblePair> set = new HashSet<ConvertiblePair>();
        set.add(cp);
        return set;
    }

    public Object convert(Object o, TypeDescriptor td, TypeDescriptor td1) {
        Object w = td.getClass();
        return o;
    }

    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
        if(sourceType.getObjectType() == String.class && targetType.isAssignableTo(TypeDescriptor.valueOf(SimpleAbstractEntity.class))){
            String idAsTxt = (String)sourceType.getSource();
            long id = Long.valueOf(idAsTxt);
        }

        return true;
    }
}

I add line in @Configuration class:

@Override
public FormattingConversionService mvcConversionService() {
    FormattingConversionService bean = super.mvcConversionService(); //To change body of generated methods, choose Tools | Templates.
    bean.addConverter(new StringToAbstractEntityConverter());
    bean.addConverter(new ArrayListToSetConverter());
    return bean;
}

But when I add a breakpoint in StringToAbstractEntityConverter app doens't stop in it. So it doesn't use this class...

I want to convert id from client to Object...

I will be very grateful if someone could help me with this :)

Best regards, Matt.