Serving Web Content with Spring MVC
This guide walks you through the process of creating a "hello world" web site with Spring.
What you’ll build
You’ll build an application that has a static home page, and also will accept HTTP GET requests at:
http://localhost:8080/greeting
and respond with a web page displaying HTML. The body of the HTML contains a greeting:
"Hello, World!"
You can customize the greeting with an optional name
parameter in the query string:
http://localhost:8080/greeting?name=User
The name
parameter value overrides the default value of "World" and is reflected in the response:
"Hello, User!"
What you’ll need
- About 15 minutes
- A favorite text editor or IDE
- JDK 1.8 or later
- Gradle 2.3+ or Maven 3.0+
- You can also import the code from this guide as well as view the web page directly into Spring Tool Suite (STS) and work your way through it from there.
How to complete this guide
Like most Spring Getting Started guides, you can start from scratch and complete each step, or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.
To start from scratch, move on to Build with Gradle.
To skip the basics, do the following:
- Download and unzip the source repository for this guide, or clone it using Git:
git clone https://github.com/spring-guides/gs-serving-web-content.git
- cd into
gs-serving-web-content/initial
- Jump ahead to Create a web controller.
When you’re finished, you can check your results against the code in gs-serving-web-content/complete
.
Build with Gradle
Build with Maven
Build with your IDE
Create a web controller
In Spring’s approach to building web sites, HTTP requests are handled by a controller. You can easily identify these requests by the @Controller
annotation. In the following example, the 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:
src/main/java/hello/GreetingController.java
package hello;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
@Controller
public class GreetingController {
@RequestMapping("/greeting")
public String greeting(@RequestParam(value="name", required=false, defaultValue="World") String name, Model model) {
model.addAttribute("name", name);
return "greeting";
}
}
This controller is concise and simple, but there’s plenty going on. Let’s break it down step by step.
The @RequestMapping
annotation ensures that HTTP requests to /greeting
are mapped to the greeting()
method.
The above example does not specify GET vs. PUT , POST , and so forth, because @RequestMapping maps all HTTP operations by default. Use @RequestMapping(method=GET) to narrow this mapping. |
@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 below and evaluates the th:text
expression to render the value of the ${name}
parameter that was set in the controller.
src/main/resources/templates/greeting.html
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head>
<title>Getting Started: Serving Web Content</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
<p th:text="‘Hello, ‘ + ${name} + ‘!‘" />
</body>
</html>
Developing web apps
A common feature of developing web apps is coding a change, restarting your app, and refreshing the browser to view the change. This entire process can eat up a lot of time. To speed up the cycle of things, Spring Boot comes with a handy module known as spring-boot-devtools.
- Enable hot swapping
- Switches template engines to disable caching
- Enables LiveReload to refresh browser automatically
- Other reasonable defaults based on development instead of production
Make the application executable
Although it is possible to package this service as a traditional WAR file for deployment to an external application server, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java main()
method. Along the way, you use Spring’s support for embedding the Tomcat servlet container as the HTTP runtime, instead of deploying to an external instance.
src/main/java/hello/Application.java
package hello;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
@SpringBootApplication
is a convenience annotation that adds all of the following:
@Configuration
tags the class as a source of bean definitions for the application context.@EnableAutoConfiguration
tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.- Normally you would add
@EnableWebMvc
for a Spring MVC app, but Spring Boot adds it automatically when it sees spring-webmvc on the classpath. This flags the application as a web application and activates key behaviors such as setting up aDispatcherServlet
. @ComponentScan
tells Spring to look for other components, configurations, and services in the thehello
package, allowing it to find the controllers.
The main()
method uses Spring Boot’s SpringApplication.run()
method to launch an application. Did you notice that there wasn’t a single line of XML? No web.xml file either. This web application is 100% pure Java and you didn’t have to deal with configuring any plumbing or infrastructure.
Build an executable JAR
You can run the application from the command line with Gradle or Maven. Or you can build a single executable JAR file that contains all the necessary dependencies, classes, and resources, and run that. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.
If you are using Gradle, you can run the application using ./gradlew bootRun
. Or you can build the JAR file using ./gradlew build
. Then you can run the JAR file:
java -jar build/libs/gs-serving-web-content-0.1.0.jar
If you are using Maven, you can run the application using ./mvnw spring-boot:run
. Or you can build the JAR file with ./mvnw clean package
. Then you can run the JAR file:
java -jar target/gs-serving-web-content-0.1.0.jar
The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead. |
Logging output is displayed. The app should be up and running within a few seconds.
Test the App
Now that the web site is running, visit http://localhost:8080/greeting, where you see:
"Hello, World!"
Provide a name
query string parameter with http://localhost:8080/greeting?name=User. Notice how the message changes from "Hello, World!" to "Hello, User!":
"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 can always be explicitly overridden through the query string.
Add a Home Page
Static resources, like HTML or JavaScript or CSS, can easily be served from your Spring Boot application just be 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 it is used as a "welcome page" if it exists, which means it will be served up as the root resource, i.e. at http://localhost:8080/
in our example. So create this file:
src/main/resources/static/index.html
<!DOCTYPE HTML>
<html>
<head>
<title>Getting Started: Serving Web Content</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
<p>Get your greeting <a href="/greeting">here</a></p>
</body>
</html>
and when you restart the app you will see the HTML at http://localhost:8080/.