表单支持bean不保留已设置的属性值

Question

i am using a form backing bean like this.

public class BeanData implements Serializable{

    private String param1;
    private String param2;
    private String param3;
    private String param4="india";

    getters setters
}

then sending bean object in model as below-

@RequestMapping(value=/formPage, method={RequestMethod.GET,RequestMethod.POST})
    public ModelAndView getPage(HttpSession session, ModelAndView modelAndView) {   

        BeanData formBean = new BeanData();
        formBean.setParam2("123456"); // this param2 doens't have any field in JSP
        modelAndView.addObject("formBean", formBean);
        modelAndView.setViewName(PAGE);

        return modelAndView;
    }
@RequestMapping(value=submitData, headers="Accept=*/*", method={RequestMethod.POST})
    public void submitData(@Valid @ModelAttribute("formBean") BeanData formBean, BindingResult result, HttpServletRequest request,HttpServletResponse response,ModelAndView modelAndView, HttpSession session) {


        LOGGER.info("param1:"+formBean.getParam1()); // Param1 has a path map in jsp field. So whatever user is puuting into form field, that is getting populated here
        LOGGER.info(" param2:"+formBean.getParam2()); // It has not been used in JSP. Though from controller it was populated before sending the bean to the jsp. but here the value is null . This is the concern
        LOGGER.info("param3:"+formBean.getParam3());// Param1 has a path map in jsp field. So whatever user is puuting into form field, that is getting populated here
        LOGGER.info("param4:"+formBean.getParam4());//thsi field also has not been used in JSP. But this property was set in bean instantiation. It is also getting retrieved successfully.


        modelAndView.setViewName(SUCCESS PAGE);

    }

My concern is, i want to set one bean property using setter method and want to pass the bean backing object to JSP. Then all the property values should be bind(what i explicitly bind using form filed path attribute and what i have already set while created the bean object) to the backing object and it should get received in controller. Please guide me where i am doing wrong.

Answer 1

If you want to just hold the value of param2 field in JSP and get it back on form submit, you can bind it using the hidden field just like below:

<form:hidden path="formBean.param2"/>

It will not be displayed in your JSP yet it will hold your value as is.

Another way would be to store your BeanData into session.

Answer 2

The model attributes are request scoped beans. Solutions you could use:

• Map your properties to hidden fields at your html form. I do not recommend that as they can be easily update at the client side.
• Use session attributes instead of model attributes, and I think it is the last option.
• What you really should do is delegate the creation of your form bean to a method annotated with @ModelAttribute instead of doing that in your getPage method.

Spring executes method annotated with @ModelAttribute before handling the requests and then will update the object with the properties coming from your form.

@ModelAttribute("formBean")
public BeanData setFormBeanModel()
{
  BeanData formBean = new BeanData();
  formBean.setParam2("123456");
  return formBean;
}

@RequestMapping(value=/formPage, method={RequestMethod.GET,RequestMethod.POST})
public ModelAndView getPage(HttpSession session, ModelAndView modelAndView) 
{ 
  modelAndView.setViewName(PAGE);

  return modelAndView;
}