68 lines
3.9 KiB
Markdown
68 lines
3.9 KiB
Markdown
# HelloSpringMVC
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Is a trivial “Hello, World” web site with SpringMVC.
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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!”
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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!”
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# Spring Initializr
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In VsCode press `cmd+shif+p` and type `Spring Initilizr`. Choose next dependencies:
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- SpringWeb
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- Thymeleaf
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- Spring Boot DevTools
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# Web Controller
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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:
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```java
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package djmil.hellomvc;
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import org.springframework.stereotype.Controller;
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import org.springframework.ui.Model;
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import org.springframework.web.bind.annotation.GetMapping;
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import org.springframework.web.bind.annotation.RequestParam;
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@Controller
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public class GreetingController {
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@GetMapping("/greeting")
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public String greeting(@RequestParam(name="name", required=false, defaultValue="World") String name, Model model) {
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// NOTE: Here we can request some data from our RESTful backend as well
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model.addAttribute("name", name);
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return "greeting"; // <<-- template
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}
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}
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```
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This controller is concise and simple, but there is plenty going on. We break it down step by step.
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The `@GetMapping` annotation ensures that HTTP GET requests to `/greeting` are mapped to the `greeting()` method.
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[`@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.
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# Model, View and a Template
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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.
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> [!note] Make sure you have Thymeleaf on your classpath. Artifact co-ordinates: `org.springframework.boot:spring-boot-starter-thymeleaf`
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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:
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```html
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<!DOCTYPE HTML>
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<html xmlns:th="http://www.thymeleaf.org">
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<head>
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<title>Getting Started: Serving Web Content</title>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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</head>
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<body>
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<p th:text="'Hello, ' + ${name} + '!'" />
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</body>
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</html>
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``` |