Converting a Spring SimpleFormController into an @Controller

In my previous post, I showed how to convert a Spring web controller class to use the @Controller annotation. In this post, I aim to show how forms in a Spring MVC application can also be converted to using annotations.

Forms in Spring are typically modelled by extending the org.springframework.web.servlet.mvc.SimpleFormController class, but using Spring annotations, they can also be simplified and defined by the @Controller annotation.

Without annotations, a SimpleFormController would be defined as below as in both a Java class and as a bean in XML.

import org.springframework.web.servlet.mvc.SimpleFormController 
  
public class PriceIncreaseFormController extends SimpleFormController { 
  
    public ModelAndView onSubmit(Object command) { 
        // Submit the form 
    } 
      
    protected Object formBackingObject(HttpServletRequest request) 
        throws ServletException { 
        // Initialize the form 
    } 
}

<bean name="/priceincrease.htm" class="springapp.web.PriceIncreaseFormController"> 
    <property name="commandName" value="priceIncrease"/> 
    <property name="commandClass" value="springapp.service.PriceIncrease"/> 
    <property name="validator"> 
        <bean class="springapp.service.PriceIncreaseValidator"/> 
    </property> 
    <property name="formView" value="priceincrease"/> 
    <property name="successView" value="home.htm"/> 
</bean>

To convert the class to use annotations, we need to add an @Controller and @RequestMapping annotation.  We can then define a simple POJO controller that does not need to extend Spring's classes.

@Controller
@RequestMapping("/priceincrease.htm") 
public class PriceIncreaseFormController { 
 
    @Autowired
    private PriceIncreaseValidator priceIncreaseValidator; 
  
    @RequestMapping(method=RequestMethod.POST) 
    public String onSubmit(@ModelAttribute("priceIncrease")PriceIncrease priceIncrease, 
        BindingResult result) { 
          
        int increase = priceIncrease.getPercentage(); 
        priceIncreaseValidator.validate(increase, result); 
        if (result.hasErrors()) 
            return "priceIncrease"; 
          
        // Validator has succeeded. 
        // Perform necessary actions and return to success page. 
        return "redirect:home.htm"; 
    } 
      
    @RequestMapping(method=RequestMethod.GET) 
    public String initializeForm(ModelMap model) { 
        // Perform and Model / Form initialization
        Map<Integer, String> priority = new LinkedHashMap<Integer, String>();
        priority.put(1, "Low");
        priority.put(2, "Normal");
        priority.put(3, "High");
 
        model.addAttribute("priorityList", priority);
  
        return "priceincrease"; 
    } 
  
    // Other getters and setters an needed. 
}

After defining the class like this, there is no need for the class to be defined within the Spring Context XML file.

The two methods outlined above in this simple class show how the initializeForm() method is called when an HTTP GET request is made to the form and how the form is submitted in the onSubmit() method via a HTTP POST request.  The method called on a GET request is used to initialize the form, whereas the method called on a POST request is called when the form is submitted.

The final thing to notice from this class is that the validation has to be explicitly called within the onSubmit() method.  In this example, the PriceValidator is injected into the class via the @Autowired annotation.