[JAVA] Hello World with Spring Boot

We are planning to develop with SpringBoot + Thymeleaf + Gradle at the next site, For both rabbits and horns, start with Hello World!

So, at first, I will simply use StringBoot and describe the procedure to display Hello World in HTML.

Development environment

OS：windows10 Pro JDK：11.0.3 IDE: STS (Spring Tool Suite) 3.9.8.RELEASE * Hereinafter referred to as STS. Build tool: Gradle 3.X

Execution procedure

1. Creation of "Spring Starter Project"

First, create a project named "Hello-sample" by following the steps below.

** 1-1. ** Select [File (or right-click on the project folder)]> [New]> [Spring Starter Project] from the STS menu.

** 1-2. ** On the screen below, enter "hello-sample" as the name, select "Gradle (Buildship 3.x)" as the type, select the Java version to use, and click the "Next" button.

** 1-3. ** On the screen below, select "Web" and "Thymeleaf" and click the "Finish" button.

You can filter by entering "Web" or "Thymeleaf" in the available field.

When you create a new project, you should see the following structure.

** 1-4. ** Right-click on the project and select Run> Spring Boot Application.

The following log is output to the STS console. If there are no errors, the "Spring Starter Project" has been created successfully.

2. Creating a screen (HTML)

Create the screen to be displayed next, that is, HTML.

** 2-1. ** Select File (or right-click on the project folder)> New> Other from the STS menu.

** 2-2. ** On the displayed screen, enter "html" in the wizard field and apply a filter. "HTML file" will be displayed. Select this and click the "Next" button.

** 2-3. ** Specify the location and file name to create the HTML file, and click the "Finish" button. -Specify the location to create: Enter the following path in [Enter or select parent folder]. 　　　hello-sample/src/main/resources/templates -Specify file name: Enter "index.html" in [File name].

** 2-4. ** Change the created HTML file so that it has the following contents.

`index.html`


<!DOCTYPE html>
<html>
  <head>
    <title>Hello</title>
    <meta charset="utf-8" />
  </head>
  <body>
    <h1>Hello SpringBoot Sample</h1>
  </body>
</html>

3. 3. Creating a Controller class

I have prepared the HTML to display, but it cannot be displayed as it is. Create a Controller class that will be "C" in MVC.

** 3-1. ** From the STS menu, select [File (or right-click on the project folder)]> [New]> [Class] and create a class with the name "HelloController".

I think it will be configured like this.

** 3-2. ** Change the created Controller class so that it has the following contents.

`HelloController.java`


package com.example.demo;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class HelloController {
    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String index(Model model) {
        return "index";  //Specify the name of the HTML file to be displayed (no extension required)
    }		
}

4. Run

Once this is done, right-click on the project> Run> Spring Boot Application to run it. After starting, try hitting the following URL from your browser. 　　URL：http://localhost:8080/

The following screen will be displayed.

that's all. In the next article, I'd like to pass a value from the Controller class.