Read: 11 - Spring

Reading-notes.md

Read: 11 - Spring

  • If I want to create a spring project i navigate to this website https://start.spring.io/.

  • it does most of configuration for me.

  • all configurations in gradle.build file.

creating and downloading project.

  1. In website mentioned I should navigate to it then.

  2. choose java as language.

  3. choose gradle build.

  4. add dependencies Spring Web, Thymeleaf, and Spring Boot DevTools.

  5. and generate.

Create a Web Controller

  • to handle web requests in java or spring I must identify method as controller. e @Controller

  • inside controller @GetMapping("/someUrl") navigate get requests to the /someUrl to this controller.

  • @RequestParam assign value to key, example @RequestParam(age=20, name="whatever").

  • the method implemented into html using templagte engine In our case Thymeleaf.

<!DOCTYPE HTML>

<head> 
    <title>card</title> 
</head>
<body>
    <p th:text="'Age: ' + ${age}" />
    <p th:text="'Hello, ' + ${name} + '!'" />
</body>
</html>

Spring Boot Devtools

  • spring-boot-devtools speed up development process.

  • for example part of developing applications is that always debugging and changing, so it’s consuming a lot of time to keep running and stop application etc…

SO what it does :

  • Enables hot swapping.

  • Switches template engines to disable caching.

  • Enables LiveReload to automatically refresh the browser.

  • Other reasonable defaults based on development instead of production.

Run the Application

  • Spring Initializr creates an application class for me.

  • class contain following:

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

    • @EnableAutoConfiguration : tell spring to add beans based on classpath.

    • @ComponentScan make spring to search for components, configs and services.

  • main() method uses Spring Boot’s SpringApplication.run() method to launch an application.

    • like this :
public static void main(String[] args) {
		SpringApplication.run(ServingWebContentApplication.class, args);
	}

Spring MVC and Thymeleaf: how to access data from templates

  • the spring app contain model and controller.

    • controller prepare the model with data then select a viewer to render it.

    • Model map make the process abstract.

  1. Spring model attributes

  • during the execution the Spring get the data that found and inject it to the thymeleaf or any rendering engine.

    • there is variable should be in the view engine with key specified and connected with model in order for proper injection.

  • That’s wht it’s called model mapping.

  • Ways of injecting data in thymeleaf:

    • in any way i am injecting to thymeleaf I will add the variable in model and it should be available in thymeleaf or any template engine.
    1. ddAttribute() method.
 @RequestMapping(value = "message", method = RequestMethod.GET)
        public String messages(Model model) {
            model.addAttribute("messages", messageRepository.findAll());
            return "message/list";
        }
  1. ModelAndView class
 @RequestMapping(value = "message", method = RequestMethod.GET)
        public ModelAndView messages() {
            ModelAndView mav = new ModelAndView("message/list");
            mav.addObject("messages", messageRepository.findAll());
            return mav;
        }
  • now for data to be accessed in thymeleaf I must specify attribute it should be between ${attributeVariable} exactly like Template literals in javaScript.

example :

 <tr th:each="message : ${messages}">
            <td th:text="${message.id}">1</td>
            <td><a href="#" th:text="${message.title}">Title ...</a></td>
            <td th:text="${message.text}">Text ...</td>
        </tr>

  1. Request parameters

    • there parameters are coming from client (URL Query parameters).

    • in order to access these parameters i must type <p th:text="${param.query}"></p>.

    • if i have multi values in parameter I will be working with them like i am working with list.

      • <p th:text="${param.query[0]}">

  2. Session attributes

    • the session attribute can be accessed like params.

    • in controller: session.setAttribute("mySessionAttribute", "someValue");

    • in thymeleaf to access it : <p th:text="${session.mySessionAttribute}" th:unless="${session == null}">[...]</p>

  3. ServletContext attributes

  • The ServletContext attributes are shared between requests and sessions. In order to access ServletContext attributes in Thymeleaf you can use the #servletContext.