Read: 11 - Spring

Spring App Basics

Getting starting with spring:

git clone
cd gs-serving-web-content/initial
Jump ahead to Create a Web Controller.
- When you finish, you can check your results against the code in gs-serving-web-content/complete

Starting with Spring Initializr

If you use Gradle, visit the Spring Initializr to generate a new project with the required dependencies (Spring Web, Thymeleaf, and Spring Boot DevTools).

Spring Boot Devtools

To speed up this refresh cycle, Spring Boot offers with a handy module known as spring-boot-devtools. Spring Boot Devtools:

Enables hot swapping(replace without rebooting the system).
Switches template engines to disable caching.
Enables LiveReload to automatically refresh the browser. -others

Run the Application

@Configuration: Tags the class as a source of bean definitions for the application context.

Test the Application

Provide a name query string parameter by visiting http://localhost:8080/greeting?name=User.
The index.html resource is special because, if it exists, it is used as a “welcome page,"serving-web-content/ which means it is served up as the root resource (that is, at http://localhost:8080/
When you restart the application, you will see the HTML at http://localhost:8080/.

Spring MVC and Thymeleaf - how to access data from templates

@Controller classes are responsible for preparing a model map with data and selecting a view to be rendered.
in the case of Thymeleaf, it is transformed into a Thymeleaf context object.

1. Spring model attributes

Spring MVC calls the pieces of data that can be accessed during the execution of views model attributes. The equivalent term in Thymeleaf language is context variables.

There are several ways of adding model attributes to a view in Spring MV:

Add attribute to Model via its addAttribute method:

@RequestMapping(value = "message", method = RequestMethod.GET)
   public String messages(Model model) {
       model.addAttribute("messages", messageRepository.findAll());
       return "message/list";
   }

Return ModelAndView with model attributes included:

 @RequestMapping(value = "message", method = RequestMethod.GET)
        public ModelAndView messages() {
            ModelAndView mav = new ModelAndView("message/list");
            mav.addObject("messages", messageRepository.findAll());
            return mav;
        }

Expose common attributes via methods annotated with @ModelAttribute:

 @ModelAttribute("messages")
        public List<Message> messages() {
            return messageRepository.findAll();
        }

in all these cases the messages attribute is added to the model and it will be available in Thymeleaf views.
In Thymeleaf, these model attributes can be accessed with the following syntax: {attributeName}.

2. Request parameters

Request parameters are passed from the client to server, Like : https://example.com/query?q=Thymeleaf+Is+Great!

If we have @Controller that sends a redirect with a request parameter:

@Controller
        public class SomeController {
            @RequestMapping("/")
            public String redirect() {
                return "redirect:/query?q=Thymeleaf+Is+Great!";
            }
        }

we use the param to access q parameter, using brackets syntax: <p th:text="${param.q[0] + ' ' + param.q[1]}" th:unless="${param.q == null}">Test</p>
another way, using the special #request object: <p th:text="${#request.getParameter('q')}" th:unless="${#request.getParameter('q') == null}">Test</p>

we can add mySessionAttribute to session, Or by using #session, that gives us direct access to the javax.servlet.http.HttpSession object.

4. ServletContext attributes

The ServletContext attributes are shared between requests and sessions.
and to access it we can use, #servletContext.

5. Spring beans

Thymeleaf allows accessing beans registered at the Spring Application Context with the @beanName syntax: <div th:text="${@urlService.getApplicationUrl()}">...</div>

@urlService refers to a Spring Bean registered at your context.