Getting started with Spring Boot

In this topic, you will learn how to create your first Spring Boot application. This application is quite simple and does nothing useful, but still, it will demonstrate the basic structure of any Spring Boot project.

Generating a Spring Boot application

It is often hard to start a new project from scratch, especially for beginners. You must set up the basic structure, create configurations and manage all external dependencies. Fortunately, a website called Spring Initializr can generate the basic Spring Boot project based on your wishes.

The site may look slightly different than the above image, but the general idea remains the same. There are several essential options you need to specify before generating a project:

• The build tool: Maven or Gradle (with build scripts written in Groovy or the Kotlin DSL).

• The JVM-based language: Java (8, 11 or higher), Kotlin or Groovy.

• The version of the Spring Boot framework (e.g., the last released version without suffixes like SNAPSHOT, M, etc.).

• Project metadata like group, artifact, description and package name.

• External dependencies: other frameworks and libraries.

In our example, we've chosen Gradle as the build tool and Java 11 as the language. You can select a more recent version if you like. Our application is named demo.

By default, the packaging type for Spring Boot applications is Jar. This means that your application will be packed in a .jar file that contains all the required dependencies. This type of file is simpler to use than a .war file, which has to be deployed on an external application server.

After choosing the necessary settings and dependencies, click Generate to get an archive with the project files. This archive contains the basic structure of a typical Spring Boot application without any application logic. It is only a template that you'd have to fill with logic yourself.

Running the application

Although the generated application is useless for now, it is a good template to start with.

Let's run it! First, unpack the application and then visit the project directory. In our examples, we will use Gradle as it is a commonly used build automation system.

First, we should build the application. In a Unix-like environment, use the following command.

./gradlew build

On Windows systems, execute the batch file using the command

gradlew build

This command uses the Gradle wrapper to create a .jar file and puts it in the build/libs/ directory. Gradle automatically downloads all the necessary dependencies while building.

When finished building, Gradle should print a message like

BUILD SUCCESSFUL in 10s

Now, it is time to run the program contained in the .jar file.

java -jar build/libs/*.jar

If you get the message

no main manifest attribute, in build/libs/demo-0.0.1-SNAPSHOT-plain.jar

target the other .jar file by running

java -jar build/libs/demo-0.0.1-SNAPSHOT.jar

or run gradlew bootRun.

While running, this application prints the Spring logo and several log lines that we skipped.

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.4.4)

You may also build and start an application using a single line. In a Unix-like environment, you can do so using the following command:

./gradlew build && java -jar build/libs/*.jar

Congratulations! You just created and started your first application using the Spring Boot framework without a single line of code except for a pair of commands.