# HelloSpringMVC
Is a trivial “Hello, World” web site with SpringMVC.
This application is an outcome of [this](https://spring.io/guides/gs/serving-web-content/) guide, which walks you through the process of creating a “Hello, World” web site with Spring. It serves a static home page and that will also accept HTTP GET requests at: http://localhost:8080/greeting. It will respond with a web page that displays HTML. The body of the HTML will contain a greeting: “Hello, World!”
You can customize the greeting with an optional name parameter in the query string. The URL might then be http://localhost:8080/greeting?name=User. The `name` parameter value overrides the default value of `World` and is reflected in the response by the content changing to “Hello, User!”
# Spring Initializr
In VsCode press `cmd+shif+p` and type `Spring Initilizr`. Choose next dependencies:
- SpringWeb
- Thymeleaf
- Spring Boot DevTools
# MVC
## Web Controller
In Spring’s approach to building web sites, HTTP requests are handled by a controller. You can easily identify the controller by the [`@Controller`](http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/stereotype/Controller.html) annotation. In the following example, `GreetingController` handles GET requests for `/greeting` by returning the name of a [`View`](http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/servlet/View.html) (in this case, `greeting`). A `View` is responsible for rendering the HTML content. The following listing (from `src/main/java/djmil/hellomvc/GreetingController.java`) shows the controller:
```java
package djmil.hellomvc;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
@Controller
public class GreetingController {
@GetMapping("/greeting")
public String greeting(@RequestParam(name="name", required=false, defaultValue="World") String name, Model model) {
// NOTE: Here we can request some data from our RESTful backend as well
model.addAttribute("name", name);
return "greeting"; // <<-- template
}
}
```
This controller is concise and simple, but there is plenty going on. We break it down step by step.
The `@GetMapping` annotation ensures that HTTP GET requests to `/greeting` are mapped to the `greeting()` method.
[`@RequestParam`](http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/bind/annotation/RequestParam.html) binds the value of the query string parameter `name` into the `name` parameter of the `greeting()` method. This query string parameter is not `required`. If it is absent in the request, the `defaultValue` of `World` is used. The value of the `name` parameter is added to a [`Model`](http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/ui/Model.html) object, ultimately making it accessible to the view template.
## Model, View and a Template
The implementation of the `greeting()` method body relies on a view technology (in this case, [Thymeleaf](http://www.thymeleaf.org/doc/tutorials/2.1/thymeleafspring.html)) to perform server-side rendering of the HTML.
> [!note] Make sure you have Thymeleaf on your classpath. Artifact co-ordinates: `org.springframework.boot:spring-boot-starter-thymeleaf`
Thymeleaf parses the `greeting.html` template and evaluates the `th:text` expression to render the value of the `${name}` parameter that was set in the controller. The following listing `src/main/resources/templates/greeting.html` shows the template:
```html
Getting Started: Serving Web Content
```
## Test the Application
Now that the web site is running, visit http://localhost:8080/greeting, where you should see “Hello, World!”
Provide a `name` query string parameter by visiting http://localhost:8080/greeting?name=User). Notice how the message changes from “Hello, World!” to “Hello, User!”:
This change demonstrates that the [`@RequestParam`](http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/bind/annotation/RequestParam.html) arrangement in `GreetingController` is working as expected. The `name` parameter has been given a default value of `World`, but it can be explicitly overridden through the query string.
# Add a Home Page
Static resources, including HTML and JavaScript and CSS, can be served from your Spring Boot application by dropping them into the right place in the source code. By default, Spring Boot serves static content from resources in the classpath at `/static` (or `/public`). The `index.html` resource is special because, if it exists, it is used as a "welcome page" for serving web-content. Which means it is served up as the root resource (that is, at `http://localhost:8080/`). For this, you need to create the following file `src/main/resources/static/index.html`:
```html
Getting Started: Serving Web Content
```
When you restart the application, you will see the HTML at http://localhost:8080/.
## Spring Boot Devtools
A common feature of developing web applications is coding a change, restarting your application, and refreshing the browser to view the change. This entire process can eat up a lot of time. To speed up this refresh cycle, Spring Boot offers with a handy module known as [spring-boot-devtools](http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#using-boot-devtools):
- Enables [hot swapping](https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#using.running-your-application.hot-swapping).
- Switches template engines to disable caching.
- Enables LiveReload to automatically refresh the browser.
- Other reasonable defaults based on development instead of production.
## Interactivity
Let's add minimal interactivity to the page by introducing an input field and a button. On the button press, a simple JavaScript will reload the page (by calling [[README#Web Controller]] 's `Get` endpoint) providing a value from the input filed as an URL parameter. Update `greeting.htm` with next lines:
```html
...