Spring form:select does not render with an option "selected" attribute - spring

Question

I'm stuck in a problem with converters and bindings.
I have a page with a form:select where I bind an list of object with itemValue
<form:select id="id_a" items="${items}" path="builder" itemValue="id" />
I've created 2 converter that convert this bean. One convert from the bean to a string displaying the description the other convert from an id to obtain the bean from the DB.
private Converter<BuilderType, String> getBuilderTypeToStringConverter(){
return new Converter<BuilderType, String>(){
public String convert(BuilderType builder){
return builder.getDescription();
}
};
}
private Converter<String,BuilderType> getStringToBuilderTypeConverter(){
return new Converter<String, BuilderType>(){
public BuilderType convert(String id){
return builderService.findById(new Long(id));
}
};
}
So when I create the bean everything works fine, I see the description in the select field and when submit the form the id gets transformed to to the real bean and put into the model attribute before reaching the controller.
the problems is when I try to update, my select is still correctly populated, but the actual value is not selected. There is no option with the attribute "selected" to initialize correctly the select.
That's really strange because I have an sample application (petclinic) of spring roo that actually with the same type of converters populate correctly the select.
The only way I found to get this working is a bit is to add ".id" to the path :
<form:select id="id_a" items="${items}" path="builder.id" itemValue="id" />
But this way on submit I receive back in the controller a empty "builder" with only the id set, not the comprete object I normaly receive when the correct converter gets invoked.
I really have no idea what could be the difference between the two applications that makes one work and not the other... even the spring library version are the same!

Answer 1

I've found the problem. It seems that in the web.xml of working application there was another filter I was not using, just adding this made everything work fine:
<filter>
<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
<filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
It's really strange because nowhere I've found that this was mandatory or even have little a connection with the spring tags to make them work as expected!

Answer 2

I think you should define equals method for the entity class (BuilderType) and compare the instances by id. Otherwise, form generation is not able to find the current value from the list of items for options.
You can verify this by checking calls to equals when implemented in BuilderType.
I was facing the same problem and was able to solve it with help of this comment and the sample code (AbstractEntity.java) in Spring Data book.