Spring MVC default GET request parameter binding to command type

Question

As I read explanation here, I found that Spring can automatically bind GET request parameter to a type. Below is the sample code from the link.

@Controller
@RequestMapping("/person")
public class PersonController {
        ...             
        @RequestMapping("/create")
        public String create(Person p) {
                //TODO: add Person to DAO
                return "person/show";
        }
}

Can someone tell me how spring do this? What bean that contains the logic to convert the parameter onto command type (Person type)?

codependent · Accepted Answer · 2014-06-23 07:42:57Z

The trick is done here: org.springframework.web.method.annotation.ModelAttributeMethodProcessor#resolveArgument()

This is the excerpt of code where it actually binds the class to the values:

String name = ModelFactory.getNameForParameter(parameter);
//Here it determines the type of the parameter and creates an instance
Object attribute = (mavContainer.containsAttribute(name)) ?
            mavContainer.getModel().get(name) : createAttribute(name, parameter, binderFactory, request);

//Then it binds the parameters from the servlet to the previously created instance
WebDataBinder binder = binderFactory.createBinder(request, attribute, name);
if (binder.getTarget() != null) {
    bindRequestParameters(binder, request);
    validateIfApplicable(binder, parameter);
    if (binder.getBindingResult().hasErrors()) {
        if (isBindExceptionRequired(binder, parameter)) {
            throw new BindException(binder.getBindingResult());
        }
    }
}

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