Spring automatic binding for dropdown lists for bean properties

Question

Hi, Is there a way to bind beans properties for another type of bean using the spring's form.select. Example:

I have a bean that needs to be updated in the view with a property called BeanB:

public class BeanA {    
  private BeanB bean;
  private int id;

  private void setId(int id){
     this.id = id;
  }

  private int getId(){
     return this.id;
  }

  public void setBean(BeanB bean){
    this.bean = bean;
  }

  public BeanB getBean(){
   return this.bean;
  }
}

public class BeanB{
    private int id;

    private void setId(int id){
       this.id = id;
    }

    private int getId(){
       return this.id;
    }
}

For the view I want to send a list of BeanB to be chosen from using the spring's formcontroller:

public class MyController extends SimpleFormController{

protected ModelAndView handleRenderRequestInternal(RenderRequest request, RenderResponse response) throws Exception {
  BeanA bean = new BeanA();
  //... init the bean or retrieve from db

  List<BeanB> list = new ArrayList<BeanB>();
  //... create list of objects

  ModelAndView modelAndView = super.handleRenderRequestInternal(request, response);
  modelAndView.getModel().put("beans", list);
  modelAndView.getModel().put("bean", bean);

  return modelAndView ;
}
}

In jsp I want to use a form.select to select the item I want to set for the BeanA from the given list, something like:

<form:select path="${bean.bean}" items="${beans}"/>

It looks like it doesn't work like this. Is there another simple solution for this?

Answer 1

To create the select markup in HTML:

<form:select path="bean" items="${candidates}" itemValue="id" itemLabel="name"/>

When the form is submitted, the value will be passed into Spring as a String, which will then need to be converted into a bean of the required type. Spring uses the WebDataBinder for this, using PropertyEditors to do the conversion to/from String. Since your 'id' attribute is probably already serializable as a String you are already seeing half of this working.

You're looking for this: http://static.springsource.org/spring/docs/2.5.6/reference/mvc.html#mvc-ann-webdatabinder

@InitBinder
protected void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(BeanB.class, new PropertyEditorSupport() {
        @Override
        public void setAsText(String text) {
            // some code to load your bean.. 
            // the example here assumes BeanB class knows how to return
            //  a bean for a specific id (which is an int/Integer) by
            //  calling the valueOf static method
            // eg:
            setValue(BeanB.valueOf(Integer.valueOf(text)));
        }
    });
}

The docs for Spring 2.5.6 seems to suggest the @Controller and @InitBinder annotations work if configured, you'll have to extrapolate for your environment.

@see http://static.springsource.org/spring/docs/2.5.6/api/index.html?org/springframework/web/bind/WebDataBinder.html