Spring Boot



Static Resources

What is Spring Boot?

Takes an opinionated view of building production-ready Spring applications. Spring Boot favors convention over configuration and is designed to get you up and running as quickly as possible. Spring Boot makes it easy to create stand-alone, production-grade Spring based Applications that you can "just run". We take an opinionated view of the Spring platform and third-party libraries so you can get started with minimum fuss. Most Spring Boot applications need very little Spring configuration.

  1. Create stand-alone Spring applications
  2. Embed Tomcat, Jetty or Undertow directly (no need to deploy WAR files)
  3. Provide opinionated 'starter' POMs to simplify your Maven configuration
  4. Automatically configure Spring whenever possible
  5. Provide production-ready features such as metrics, health checks and externalized configuration
  6. Absolutely no code generation and no requirement for XML configuration

How can we get started with Spring Boot?

We can use https://start.spring.io/ to generate a maven project, download the zip file, extract it, and import it into Eclipse. When we do this, Maven automatically download all the dependencies, etc.

What is the purpose of the @EnableAutoConfiguration annotation?

This annotation tells Spring Boot to “guess” how you will want to configure Spring, based on the jar dependencies that you have added. Since spring-boot-starter-web added Tomcat and Spring MVC, the auto-configuration will assume that you are developing a web application and setup Spring accordingly.

What is the purpose of the main method?

This is just a standard method that follows the Java convention for an application entry point. Our main method delegates to Spring Boot’s SpringApplication class by calling run. SpringApplication will bootstrap our application, starting Spring which will in turn start the auto-configured Tomcat web server. We need to pass Example.class as an argument to the run method to tell SpringApplication which is the primary Spring component. The args array is also passed through to expose any command-line arguments.

import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.stereotype.*;
import org.springframework.web.bind.annotation.*;

public class Example {

    String home() {
        return "Hello World!";

    public static void main(String[] args) throws Exception {
        SpringApplication.run(Example.class, args);

How can we run our application from command line?

Since we have used the spring-boot-starter-parent POM we have a useful run goal that we can use to start the application. Type:

mvn spring-boot:run

from the root project directory to start the application. If you open a web browser to localhost:8080 you should see the following output:

Hello World!

How can we create the executable JAR for our Spring Boot application?

Let’s finish our example by creating a completely self-contained executable jar file that we could run in production. Executable jars (sometimes called “fat jars”) are archives containing your compiled classes along with all of the jar dependencies that your code needs to run.

To create an executable jar we need to add the spring-boot-maven-plugin to our pom.xml. Insert the following lines just below the dependencies section:


The spring-boot-starter-parent POM includes <executions> configuration to bind the repackage goal. If you are not using the parent POM you will need to declare this configuration yourself. See the plugin documentation for details.

Save your pom.xml and run mvn package from the command line:

mvn package

If you look in the target directory you should see myproject-0.0.1-SNAPSHOT.jar. The file should be around 10 Mb in size. If you want to peek inside, you can use jar tvf:

jar tvf target/myproject-0.0.1-SNAPSHOT.jar

You should also see a much smaller file named myproject-0.0.1-SNAPSHOT.jar.original in the target directory. This is the original jar file that Maven created before it was repackaged by Spring Boot. To run that application, use the java -jar command:

java -jar target/myproject-0.0.1-SNAPSHOT.jar
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