Spring Boot Hello World Example

By mkyong | Updated: August 15, 2023

Viewed: 40,589 (+386 pv/w)

In this article, we will show you a simple Spring Boot web application, publish an endpoint /, access it, and the endpoint / will return a String hello world as a result.

Technologies used:

Spring Boot 3.1.2
Java 17
Maven 3.8.6

Table of contents:

1. Project Directory
2. Spring Boot Maven Dependencies
3. Project Dependencies in Tree Structure
4. Spring Boot Web Application
5. Spring Boot Entry Point
6. Add Unit Test
- 6.1 MockMvc
- 6.2 TestRestTemplate
7. Demo
8. Create an executable JAR
9. Download Source Code
10. References

Note
Spring Boot 3.x requires Java 17.

1. Project Directory

A standard Maven folder Structure.

2. Spring Boot Maven Dependencies

The spring-boot-starter-parent provide a base version for the Spring Boot applications. To develop web-related services, put spring-boot-starter-web.

pom.xml


    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.1.2</version>
        <relativePath/> <!-- lookup parent from repository, not local -->
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

Below is the complete pom.xml.

pom.xml


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <artifactId>spring-boot-hello-world</artifactId>
    <packaging>jar</packaging>
    <name>Spring Boot Hello World Example</name>
    <version>1.0</version>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.1.2</version>
        <relativePath/> <!-- lookup parent from repository, not local -->
    </parent>

    <properties>
        <java.version>17</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.11.0</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>

        </plugins>
    </build>

</project>

3. Project Dependencies in Tree Structure

For Spring Boot 3, the spring-boot-starter-web bring in the following main dependencies:

Spring boot configuration stuff.
Spring web mvc components.
Embedded Tomcat 10.1.11.
Slf4j logback for logging.
Snakeyaml for external YAML properties.
Jackson 2.x for JSON binding.

In Maven, we can use mvn dependency:tree to review the project dependencies in a tree structure.

Terminal


$ mvn dependency:tree

[INFO] org.springframework.boot:spring-boot-hello-world:jar:1.0
[INFO] +- org.springframework.boot:spring-boot-starter-web:jar:3.1.2:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter:jar:3.1.2:compile
[INFO] |  |  +- org.springframework.boot:spring-boot:jar:3.1.2:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-autoconfigure:jar:3.1.2:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-starter-logging:jar:3.1.2:compile
[INFO] |  |  |  +- ch.qos.logback:logback-classic:jar:1.4.8:compile
[INFO] |  |  |  |  \- ch.qos.logback:logback-core:jar:1.4.8:compile
[INFO] |  |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.20.0:compile
[INFO] |  |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.20.0:compile
[INFO] |  |  |  \- org.slf4j:jul-to-slf4j:jar:2.0.7:compile
[INFO] |  |  +- jakarta.annotation:jakarta.annotation-api:jar:2.1.1:compile
[INFO] |  |  \- org.yaml:snakeyaml:jar:1.33:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-json:jar:3.1.2:compile
[INFO] |  |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.15.2:compile
[INFO] |  |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.15.2:compile
[INFO] |  |  |  \- com.fasterxml.jackson.core:jackson-core:jar:2.15.2:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.15.2:compile
[INFO] |  |  +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.15.2:compile
[INFO] |  |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.15.2:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-tomcat:jar:3.1.2:compile
[INFO] |  |  +- org.apache.tomcat.embed:tomcat-embed-core:jar:10.1.11:compile
[INFO] |  |  +- org.apache.tomcat.embed:tomcat-embed-el:jar:10.1.11:compile
[INFO] |  |  \- org.apache.tomcat.embed:tomcat-embed-websocket:jar:10.1.11:compile
[INFO] |  +- org.springframework:spring-web:jar:6.0.11:compile
[INFO] |  |  +- org.springframework:spring-beans:jar:6.0.11:compile
[INFO] |  |  \- io.micrometer:micrometer-observation:jar:1.11.2:compile
[INFO] |  |     \- io.micrometer:micrometer-commons:jar:1.11.2:compile
[INFO] |  \- org.springframework:spring-webmvc:jar:6.0.11:compile
[INFO] |     +- org.springframework:spring-aop:jar:6.0.11:compile
[INFO] |     +- org.springframework:spring-context:jar:6.0.11:compile
[INFO] |     \- org.springframework:spring-expression:jar:6.0.11:compile
[INFO] \- org.springframework.boot:spring-boot-starter-test:jar:3.1.2:test
[INFO]    +- org.springframework.boot:spring-boot-test:jar:3.1.2:test
[INFO]    +- org.springframework.boot:spring-boot-test-autoconfigure:jar:3.1.2:test
[INFO]    +- com.jayway.jsonpath:json-path:jar:2.8.0:test
[INFO]    |  \- org.slf4j:slf4j-api:jar:2.0.7:compile
[INFO]    +- jakarta.xml.bind:jakarta.xml.bind-api:jar:4.0.0:test
[INFO]    |  \- jakarta.activation:jakarta.activation-api:jar:2.1.2:test
[INFO]    +- net.minidev:json-smart:jar:2.4.11:test
[INFO]    |  \- net.minidev:accessors-smart:jar:2.4.11:test
[INFO]    |     \- org.ow2.asm:asm:jar:9.3:test
[INFO]    +- org.assertj:assertj-core:jar:3.24.2:test
[INFO]    |  \- net.bytebuddy:byte-buddy:jar:1.14.5:test
[INFO]    +- org.hamcrest:hamcrest:jar:2.2:test
[INFO]    +- org.junit.jupiter:junit-jupiter:jar:5.9.3:test
[INFO]    |  +- org.junit.jupiter:junit-jupiter-api:jar:5.9.3:test
[INFO]    |  |  +- org.opentest4j:opentest4j:jar:1.2.0:test
[INFO]    |  |  +- org.junit.platform:junit-platform-commons:jar:1.9.3:test
[INFO]    |  |  \- org.apiguardian:apiguardian-api:jar:1.1.2:test
[INFO]    |  +- org.junit.jupiter:junit-jupiter-params:jar:5.9.3:test
[INFO]    |  \- org.junit.jupiter:junit-jupiter-engine:jar:5.9.3:test
[INFO]    |     \- org.junit.platform:junit-platform-engine:jar:1.9.3:test
[INFO]    +- org.mockito:mockito-core:jar:5.3.1:test
[INFO]    |  +- net.bytebuddy:byte-buddy-agent:jar:1.14.5:test
[INFO]    |  \- org.objenesis:objenesis:jar:3.3:test
[INFO]    +- org.mockito:mockito-junit-jupiter:jar:5.3.1:test
[INFO]    +- org.skyscreamer:jsonassert:jar:1.5.1:test
[INFO]    |  \- com.vaadin.external.google:android-json:jar:0.0.20131108.vaadin1:test
[INFO]    +- org.springframework:spring-core:jar:6.0.11:compile
[INFO]    |  \- org.springframework:spring-jcl:jar:6.0.11:compile
[INFO]    +- org.springframework:spring-test:jar:6.0.11:test
[INFO]    \- org.xmlunit:xmlunit-core:jar:2.9.1:test
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  5.728 s
[INFO] Finished at: 2023-08-15T14:57:04+08:00
[INFO] ------------------------------------------------------------------------

4. Spring Boot Web Application

The @RestController annotation is the controller to handle incoming HTTP web requests, equivalent to @Controller and @ResponseBody. The @RequestMapping("/") annotation is for routing; it mapped the HTTP web request with a / path to the hello() method.

HelloController.java


package com.mkyong;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

// @Controller
// @ResponseBody
@RestController
public class HelloController {

    @RequestMapping("/")
    String hello() {
        return "Hello World, Spring Boot!";
    }

}

5. Spring Boot Entry Point

Create a @SpringBootApplication annotated class, which is the main entry point for the Spring boot application. Run this class, and it will start the entire Spring Boot web application.

MainApplication.java


package com.mkyong;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MainApplication {

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

}

6. Add Unit Test

Below are two examples of writing unit tests for the spring boot web applications.

6.1 MockMvc

We can use MockMvc to perform the test on the path /. The MockMvc mocks all MVC components; it’s fast because there is no need to start an entire HTTP server.

HelloControllerTests.java


package com.mkyong;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;

import static org.hamcrest.Matchers.equalTo;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@SpringBootTest
@AutoConfigureMockMvc
public class HelloControllerTests {

    @Autowired
    private MockMvc mvc;

    @Test
    public void welcome_ok() throws Exception {
        mvc.perform(MockMvcRequestBuilders.get("/").accept(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk())
                .andExpect(content().string(equalTo("Hello World, Spring Boot!")));
    }

}

6.2 TestRestTemplate

Alternatively, we can use TestRestTemplate to perform the same test. It requires a running server, usually with a random port, and making actual HTTP requests to the running server.

HelloControllerTests2.java


package com.mkyong;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.http.ResponseEntity;

import static org.assertj.core.api.AssertionsForClassTypes.assertThat;

//@SpringBootTest(classes = MainApplication.class, webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class HelloControllerTests2 {

  @Autowired
  private TestRestTemplate template;

  @Test
  public void hello_ok() throws Exception {
      ResponseEntity<String> response = template.getForEntity("/", String.class);
      assertThat(response.getBody()).isEqualTo("Hello World, Spring Boot!");
  }

}

7. Demo

Navigate to the project folder and type mvn spring-boot:run to run the spring boot application.

Terminal


  $ mvn spring-boot:run

By default, Spring Boot starts a self-embedded Tomcat at port 8080 and deploys the spring boot web application.

Terminal


$ mvn spring-boot:run

.   ____          _            __ _ _
/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/  ___)| |_)| | | | | || (_| |  ) ) ) )
'  |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot ::                (v3.1.2)

com.mkyong.MainApplication               : Starting MainApplication using Java 17 with PID 53029 (...)
com.mkyong.MainApplication               : No active profile set, falling back to 1 default profile: "default"
o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
o.apache.catalina.core.StandardService   : Starting service [Tomcat]
o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.11]
o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 487 ms
o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
com.mkyong.MainApplication               : Started MainApplication in 0.923 seconds (process running for 1.105)

P.S We can press ctrl + c to exit the Spring Boot application.

We can use curl to send an HTTP request to the / endpoint.

Terminal


curl localhost:8080

Hello World, Spring Boot!

Or you can open a browser and access the http://localhost:8080/; the browser will return a plain text Hello World, Spring Boot!.

8. Create an executable JAR

8.1 In pom.xml, the packaging is jar; it tells Maven to package the project as a jar file.

pom.xml


  <artifactId>spring-boot-hello-world</artifactId>
  <packaging>jar</packaging>
  <name>Spring Boot Hello World Example</name>
  <version>1.0</version>

And the spring-boot-maven-plugin allows Maven easier to package the Spring Boot project as an executable jar file.

Terminal


  <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
  </plugin>

8.2 A standard mvn package will compile and pack everything into an executable JAR file.


$ cd [project-path]

$ mvn clean package

$ java -jar target/spring-boot-hello-world-1.0.jar

9. Download Source Code

$ git clone https://github.com/mkyong/spring-boot.git

$ cd spring-boot-hello-world

$ mvn spring-boot:run

10. References

Spring Boot Guides
Building an Application with Spring Boot
Serving Web Content with Spring MVC
Apache Maven Compiler Plugin
Spring REST Hello World Example
Spring Boot + JUnit 5 + Mockito
common application properties
Snakeyaml for external YAML properties.
Jackson 2.x for JSON binding.

About Author

mkyong

Founder of Mkyong.com, love Java and open source stuff. Follow him on Twitter. If you like my tutorials, consider make a donation to these charities.

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Nagamani

1 year ago

Wonderful sir for starters.
I am looking for springBoot with microservice sample and simple example to start up

vamsi

1 year ago

good content

eric

1 year ago

Thank You

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