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You will build an application that has 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!”

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For all Spring applications, you should start with the Spring Initializr. The Initializr offers a fast way to pull in all the dependencies you need for an application and does a lot of the setup for you. This example needs the Spring Web, Thymeleaf, and Spring Boot DevTools dependencies.

The following listing shows the pom.xml file that is created when you choose Maven:

The following listing shows the build.gradle file that is created when you choose Gradle:

In Spring’s approach to building web sites, HTTP requests are handled by a controller. You can easily identify the controller by the @Controller annotation. In the following example, GreetingController handles GET requests for /greeting by returning the name of a View (in this case, greeting). A View is responsible for rendering the HTML content. The following listing (from src/main/java/com/example/servingwebcontent/GreetingController.java) shows the controller:

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 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 object, ultimately making it accessible to the view template.

The implementation of the method body relies on a view technology (in this case, Thymeleaf) to perform server-side rendering of the HTML. 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 (from src/main/resources/templates/greeting.html) shows the greeting.html template:

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. Spring Boot Devtools:

• 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.

The Spring Initializr creates an application class for you. In this case, you need not further modify the class provided by the Spring Initializr. The following listing (from src/main/java/com/example/servingwebcontent/ServingWebContentApplication.java) shows the application class:

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Logging output is displayed. The application should be up and running within a few seconds.

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 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.

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,"serving-web-content/ which means it is served up as the root resource (that is, at `http://localhost:8080/). As a result, you need to create the following file (which you can find in src/main/resources/static/index.html):

When you restart the application, you will see the HTML at http://localhost:8080/.

Congratulations! You have just developed a web page by using Spring.

The following guides may also be helpful:

• Building an Application with Spring Boot

• Accessing Data with GemFire

• Accessing Data with JPA

• Accessing Data with MongoDB

• Accessing data with MySQL

• Testing the Web Layer

• Building a RESTful Web Service

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