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 a service that will accept HTTP GET requests at:

http://localhost:8080/greeting
           

and respond with a web page displaying 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 6 or later
• Gradle 1.8+ 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 all Spring's 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 Set up the project.

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

.

Set up the project

First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Gradle and Maven is included here. If you're not familiar with either, refer to Building Java Projects with Gradle or Building Java Projects with Maven.

Create the directory structure

In a project directory of your choosing, create the following subdirectory structure; for example, with 

mkdir -p src/main/java/hello

 on *nix systems:

└── src
    └── main
        └── java
            └── hello
           

Create a Gradle build file

Below is the initial Gradle build file. But you can also use Maven. The pom.xml file is included right here. If you are using Spring Tool Suite (STS), you can import the guide directly.

build.gradle

buildscript {
    repositories {
        maven { url "http://repo.spring.io/libs-milestone" }
        mavenLocal()
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'

jar {
    baseName = 'gs-serving-web-content'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
    maven { url "http://repo.spring.io/libs-milestone" }
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:0.5.0.M5")
    compile("org.thymeleaf:thymeleaf-spring3:2.0.17")
    testCompile("junit:junit:4.11")
}

task wrapper(type: Wrapper) {
    gradleVersion = '1.8'
}
           

Note: This guide is using Spring Boot.

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.

Note: 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 caseThymeleaf, 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>
      

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.

Create an Application class

src/main/java/hello/Application.java

package hello;

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.ComponentScan;

@ComponentScan
@EnableAutoConfiguration
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}
      

The 

main()

 method defers to the 

SpringApplication

 helper class, providing

Application.class

 as an argument to its 

run()

 method. This tells Spring to read the annotation metadata from 

Application

 and to manage it as a component in the Spring application context.

The 

@ComponentScan

 annotation tells Spring to search recursively through the

hello

 package and its children for classes marked directly or indirectly with Spring's 

@Component

 annotation. This directive ensures that Spring finds and registers the 

GreetingController

, because it is marked with 

@Controller

, which in turn is a kind of 

@Component

 annotation.

The 

@EnableAutoConfiguration

 annotation switches on reasonable default behaviors based on the content of your classpath. For example, because the application depends on the embeddable version of Tomcat (tomcat-embed-core.jar), a Tomcat server is set up and configured with reasonable defaults on your behalf. And because the application also depends on Spring MVC (spring-webmvc.jar), a Spring MVC 

DispatcherServlet

 is configured and registered for you — no 

web.xml

 necessary! Auto-configuration is a powerful, flexible mechanism. See the API documentation for further details.

Build an executable JAR

Now that your 

Application

 class is ready, you simply instruct the build system to create a single, executable jar containing everything. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

Below are the Gradle steps, but if you are using Maven, you can find the updated pom.xml right here and build it by typing 

mvn clean package

.

Update your Gradle 

build.gradle

 file's 

buildscript

 section, so that it looks like this:

buildscript {
    repositories {
        maven { url "http://repo.spring.io/libs-snapshot" }
        mavenLocal()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:0.5.0.M4")
    }
}
      

Further down inside 

build.gradle

, add the following to the list of applied plugins:

You can see the final version of 

build.gradle

 right here.

The Spring Boot gradle plugin collects all the jars on the classpath and builds a single "über-jar", which makes it more convenient to execute and transport your service. It also searches for the 

public static void main()

 method to flag as a runnable class.

Now run the following command to produce a single executable JAR file containing all necessary dependency classes and resources:

$ ./gradlew build
      

If you are using Gradle, you can run the JAR by typing:

$ java -jar build/libs/gs-serving-web-content-0.1.0.jar
      

If you are using Maven, you can run the JAR by typing:

$ java -jar target/gs-serving-web-content-0.1.0.jar
      

Note: The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead.

Run the service

If you are using Gradle, you can run your service at the command line this way:

$ ./gradlew clean build && java -jar build/libs/gs-serving-web-content-0.1.0.jar
      

Note: If you are using Maven, you can run your service by typing

mvn clean package && java -jar target/gs-serving-web-content-0.1.0.jar

.

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

Test the service

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.

Summary

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