Spring-MVC with annotations

Introduction#

In this topic you’ll read about annotations mainly related to Spring MVC. Some of the related annotations are as follows: @Controller, @RequestMapping, @RequestParam, @RequestBody, @ResponseBody, @RestController, @ModelAttribute, @ControllerAdvice, @ExceptionHandler, @ResponseStatus.

Of course there’re more annotations which are extremly important as well but not belong directly to Spring MVC. Such as: @Required, @Autowired, @Resource, and many more.

Parameters#

Annotation	Explanation
`@Controller`	With `@Controller` annotation you mark a Java Class as a Class that holds HTTP handlers, in other words, HTTP access points to your application.
`@RequestMapping`	The `@RequestMapping` annotation is the one that you’ll use to mark HTTP handlers (HTTP access points to your application) within your `@Controller` Class
`@RequestParam`	Use the `@RequestParam` annotation to bind request parameters to a method parameter in your controller.

dispatcher-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="https://www.springframework.org/schema/beans"
    xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
    xmlns:mvc="https://www.springframework.org/schema/mvc"
    xmlns:context="https://www.springframework.org/schema/context"
    xsi:schemaLocation="https://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd
        https://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
        https://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context-4.3.xsd">
    
    
    <mvc:annotation-driven/>
    <context:component-scan base-package="your.base.package.to.scan" />
</beans>

With these two lines of configuration, you’ll enable the usage of MVC annotations.

@Controller & @RequestMapping

@Controller
@RequestMapping("/appointments")
public class AppointmentsController {

//your handlers here, for example:

@RequestMapping(path = "/new", method = RequestMethod.GET)
public AppointmentForm getNewForm() {
    return new AppointmentForm();
}

@RequestMapping(method = RequestMethod.POST)
public String add(@Valid AppointmentForm appointment, BindingResult result) {
    if (result.hasErrors()) {
        return "appointments/new";
    }
    appointmentBook.addAppointment(appointment);
    return "redirect:/appointments";
}

}

With @Controller annotation you’ll mark a Java Class as a Class that holds several HTTP handlers, in other words, HTTP access points to your application.

The @RequestMapping annotation is the one that you’ll use to mark HTTP handlers (HTTP access points to your application) within your @Controller Class

@RequestParam

@Controller
public class EditPetForm {

    @RequestMapping("/pets")
    public String setupForm(@RequestParam("petId") int petId, ModelMap model) {
        Pet pet = this.clinic.loadPet(petId);
        model.addAttribute("pet", pet);
        return "petForm";
    }
}

Important to mention, but pretty obvious, is that @RequestParam is intended to work when using HTTP GET method only because only with GET you can send a query string with parameters, and @RequestParam you can bind parameters in the query string to your controller handler parameters.