PROBLEM

In the context of Spring MVC, a model generally represents the data that will be passed to and from an operation (defined in a web controller) and the view. Spring MVC supports various options and patterns for defining the data that can be passed back and forth, and a typical Spring MVC application may use a combination of these options. The flexibility of Spring MVC to have fine-grained control for defining models is very powerfull, however along with the flexibility comes considerable variability and complexity in the implemenation using Spring.

SOLUTION

Through the use of code generation in Skyway Builder, the complexity of Spring models can be abstracted to makes things simpler for the developer.

A controller method in Spring can support zero-to-many input parameters, and the principal mechanisms in Spring for specifying input parameters are the @RequestParam and the @ModelAttribute annotations. The @RequestParam annotation is used to bind individual request parameters, like string and integers, to method parameters in the controller. The @ModelAttribute annotation is used to bind complex objects, like domain objects, data transfer objects and/or form backing objects, to method parameters in a controller.

In Skyway Builder operations are used to define request handlers (controller methods), and operation parameters are simply configured using Input variables. Since these variables are available to be processed by the operation, the developer using Skyway Builder doesn't really need to be concerned with the details of Spring.

Nevertheless here's an overview of what gets generated for input variables added to an operation::

A controller method in Spring can also output model data, and the principal mechanism in Spring for specifying output model data is the ModelAndView object. In the event that there isn't any data to be returned by the method, the controller method can simply return a String that represents the view that should be rendered. If the controller method does return data, then a ModalAndView object needs to be instantiated and each output variable is added as a model attribute to the ModelAndView object.

In Skyway Builder you simply need to define output parameters on the Operation, and Skyway Builder will handle all the details regarding how the model data should be emitted.

Here's an overview of what occurs regarding output variables added to an operation:

HOW IT WORKS

Once again a model generally refers to the data that is pased to and from a controller method (Skyway Operation).

Figure 2.5. Model (MVC)

Controller methods parameters are defined using Operation Input and Variables.

Let's examine a few scenarios to see exactly what gets generated based on the configuration of the operation inputs and outputs.

Example 1

In this first example, an operation was defined with two input variables and no output variables.

Figure 2.6. Spring MVC Model (Example 1) - Operation Inputs/Outputs

@RequestMapping(value = "/OrderCheckoutController/AddBillingAddress.action")
public String addBillingAddress(@RequestParam("orderId") String orderId, 
                                @ModelAttribute("billingAddress") Address billingAddress) throws java.lang.Exception {

  //method implementation either hand-coded or generated from action model

  return "/billingoverview.jsp";
}

Example 2

In this second example, an operation was defined with one input variable and an output variable. The output variable is mapped to an operation variable (shippingOptions) that is defined in the Variables tab (not shown).

Figure 2.7. Spring MVC Model (Example 2) - Operation Inputs/Outputs

@RequestMapping(value = "/OrderCheckoutController/LoadShippingOptions.action")
public ModelAndView loadShippingOptions(@RequestParam("zipcode") String zipcode) throws java.lang.Exception {
  ModelAndView mav = new ModelAndView();
  Set<ShippingOption> shippingOptions = null;

  //method implementation either hand-coded or generated from action model

  mav.addObject("shipoptions", shippingOptions);
  mav.setViewName("/success.jsp");
  return mav;
}

RELATED RECIPES