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.

In website mentioned I should navigate to it then.
choose java as language.
choose gradle build.
add dependencies Spring Web, Thymeleaf, and Spring Boot DevTools.
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); }

### Build an executable JAR
* to run app from terminal I can use gradle or maven gradle.
* use **gradle** to run the app:
  * `./gradlew bootRun`
  

### Test the Application
* when i run `./gradlew bootRun` can open it in browser.
* to do so I can find it on this url http://localhost:8080/greeting
* If i want to change name i can change parameter value to do so I can hit this url :
  * http://localhost:8080/greeting?name=Yazan

##### Add a Home Page
* I can add Static resources, including HTML and JavaScript and CSS in resources file that in src folder.
* By default, Spring Boot serves static resources from resources in the classpath at `/static` or `/public`

## 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.
  [resource](https://www.thymeleaf.org/doc/articles/springmvcaccessdata.html)

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”; }

[resource](https://www.thymeleaf.org/doc/articles/springmvcaccessdata.html)

2. `ModelAndView class`

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

 
[resource](https://www.thymeleaf.org/doc/articles/springmvcaccessdata.html).

* now for data to be accessed in thymeleaf I must specify attribute  it should be between `${attributeVariable}` exactly like **Template literals** in javaScript.
example : 

1 Title ... Text ...

[resource](https://www.thymeleaf.org/doc/articles/springmvcaccessdata.html).

2. **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]}">`
3. **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>`
4. **ServletContext attributes**
 * since i dont know what exactly is this yet: [resource](https://www.thymeleaf.org/doc/articles/springmvcaccessdata.html)
* The ServletContext attributes are shared between requests and sessions. In order to access ServletContext attributes in Thymeleaf you can use the #servletContext. prefix: 
* Example:

My context attribute	42
javax.servlet.context.tempdir	/tmp

```

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