Spring Boot - Bootstrapping

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This chapter will explain you how to perform bootstrapping on a Spring Boot application.

Spring Initializer

One of the ways to Bootstrapping a Spring Boot application is by using Spring Initializer. To do this, you will have to visit the Spring Initializer web page www.start.spring.io and choose your Build, Spring Boot Version and platform. Also, you need to provide a Group, Artifact and required dependencies to run the application.

Observe the following screenshot that shows an example where we added the spring-boot-starter-web dependency to write REST Endpoints.

Spring Initializer

Once you provided the Group, Artifact, Dependencies, Build Project, Platform and Version, click Generate Project button. The zip file will download and the files will be extracted.

This section explains you the examples by using both Maven and Gradle.

Maven

After you download the project, unzip the file. Now, your pom.xml file looks as shown below −

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>3.3.3</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>demo</name>
   <description>Demo project for Spring Boot</description>
   <url/>
   <licenses>
      <license/>
   </licenses>
   <developers>
      <developer/>
   </developers>
   <scm>
      <connection/>
      <developerConnection/>
      <tag/>
      <url/>
   </scm>
   <properties>
      <java.version>21</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>
      </plugins>
   </build>
</project>

Gradle

In case of Gradle, you can check the build.gradle as following:

build.gradle

buildscript {
   ext {
      springBootVersion = '3.3.3'
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'

group = 'com.tutorialspoint'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 21

repositories {
   mavenCentral()
}
dependencies {
   compile('org.springframework.boot:spring-boot-starter-web')
   testCompile('org.springframework.boot:spring-boot-starter-test')
}

Class Path Dependencies

Spring Boot provides a number of Starters to add the jars in our class path. For example, for writing a Rest Endpoint, we need to add the spring-boot-starter-web dependency in our class path. Observe the codes shown below for a better understanding −

Maven dependency

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

Gradle dependencies

dependencies {
   compile('org.springframework.boot:spring-boot-starter-web')
}

Main Method

The main method should be writing the Spring Boot Application class. This class should be annotated with @SpringBootApplication. This is the entry point of the spring boot application to start. You can find the main class file under src/java/main directories with the default package.

In this example, the main class file is located at the src/java/main directories with the default package com.tutorialspoint.demo. Observe the code shown here for a better understanding −

package com.tutorialspoint.demo;

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

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

Write a Rest Endpoint

To write a simple Hello World Rest Endpoint in the Spring Boot Application main class file itself, follow the steps shown below −

  • Firstly, add the @RestController annotation at the top of the class.

  • Now, write a Request URI method with @GetMapping annotation.

  • Then, the Request URI method should return the Hello World string.

Now, your main Spring Boot Application class file will look like as shown in the code given below −

package com.tutorialspoint.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@SpringBootApplication
public class DemoApplication {

   public static void main(String[] args) {
      SpringApplication.run(DemoApplication.class, args);
   }
   @GetMapping(value = "/")
   public String hello() {
      return "Hello World";
   }
}

Create an Executable JAR

Let us create an executable JAR file to run the Spring Boot application by using Maven commands in the command prompt as shown below −

Use the Maven command mvn clean install as shown below −

E:\dev\demo>mvn clean install

You'll see the result similar to as below:

[INFO] Scanning for projects...
[INFO] 
[INFO] [1m----------------------< [0;36mcom.tutorialspoint:demo[0;1m >-----------------------[m
[INFO] [1mBuilding demo 0.0.1-SNAPSHOT[m
[INFO]   from pom.xml
[INFO] [1m--------------------------------[ jar ]---------------------------------[m
[INFO] Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-install-plugin/3.1.3/maven-install-plugin-3.1.3.pom
....
[INFO] 
[INFO] [1m--- [0;32mclean:3.3.2:clean[m [1m(default-clean)[m @ [36mdemo[0;1m ---[m
[INFO] Deleting E:\Dev\demo\target
[INFO] 
[INFO] [1m--- [0;32mresources:3.3.1:resources[m [1m(default-resources)[m @ [36mdemo[0;1m ---[m
[INFO] Copying 1 resource from src\main\resources to target\classes
[INFO] Copying 0 resource from src\main\resources to target\classes
[INFO] 
...
[INFO] 
[INFO] [1m--- [0;32msurefire:3.2.5:test[m [1m(default-test)[m @ [36mdemo[0;1m ---[m
[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
[INFO] Downloading from central: https://repo.maven.apache.org/maven2/org/junit/platform/junit-platform-launcher/1.10.3/junit-platform-launcher-1.10.3.pom
[INFO] Downloaded from central: https://repo.maven.apache.org/maven2/org/junit/platform/junit-platform-launcher/1.10.3/junit-platform-launcher-1.10.3.pom (3.0 kB at 13 kB/s)
[INFO] 
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.tutorialspoint.demo.[1mDemoApplicationTests[m
17:35:15.626 [main] INFO org.springframework.test.context.support.AnnotationConfigContextLoaderUtils -- Could not detect default configuration classes for test class [com.tutorialspoint.demo.DemoApplicationTests]: DemoApplicationTests does not declare any static, non-private, non-final, nested classes annotated with @Configuration.
17:35:15.802 [main] INFO org.springframework.boot.test.context.SpringBootTestContextBootstrapper -- Found @SpringBootConfiguration com.tutorialspoint.demo.DemoApplication for test class com.tutorialspoint.demo.DemoApplicationTests

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

 :: Spring Boot ::                (v3.3.3)

2024-09-02T17:35:16.380+05:30  INFO 6204 --- [demo] [           main] c.t.demo.DemoApplicationTests            : Starting DemoApplicationTests using Java 21.0.3 with PID 6204 (started by Tutorialspoint in E:\Dev\demo)
2024-09-02T17:35:16.381+05:30  INFO 6204 --- [demo] [           main] c.t.demo.DemoApplicationTests            : No active profile set, falling back to 1 default profile: "default"
2024-09-02T17:35:18.173+05:30  INFO 6204 --- [demo] [           main] c.t.demo.DemoApplicationTests            : Started DemoApplicationTests in 2.162 seconds (process running for 4.295)
...
[INFO] Results:
[INFO] 
[INFO] [1;32mTests run: 1, Failures: 0, Errors: 0, Skipped: 0[m
[INFO] 
[INFO] 
[INFO] [1m--- [0;32mjar:3.4.2:jar[m [1m(default-jar)[m @ [36mdemo[0;1m ---[m
[INFO] Building jar: E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar
[INFO] 
[INFO] [1m--- [0;32mspring-boot:3.3.3:repackage[m [1m(repackage)[m @ [36mdemo[0;1m ---[m
[INFO] Replacing main artifact E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar with repackaged archive, adding nested dependencies in BOOT-INF/.
[INFO] The original artifact has been renamed to E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar.original
[INFO] 
[INFO] [1m--- [0;32minstall:3.1.3:install[m [1m(default-install)[m @ [36mdemo[0;1m ---[m
....
[INFO] Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-xml/3.0.1/plexus-xml-3.0.1.jar (94 kB at 806 kB/s)
[INFO] Installing E:\Dev\demo\pom.xml to C:\Users\Tutorialspoint\.m2\repository\com\tutorialspoint\demo\0.0.1-SNAPSHOT\demo-0.0.1-SNAPSHOT.pom
[INFO] Installing E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar to C:\Users\Tutorialspoint\.m2\repository\com\tutorialspoint\demo\0.0.1-SNAPSHOT\demo-0.0.1-SNAPSHOT.jar
[INFO] [1m------------------------------------------------------------------------[m
[INFO] [1;32mBUILD SUCCESS[m
[INFO] [1m------------------------------------------------------------------------[m
[INFO] Total time:  18.938 s
[INFO] Finished at: 2024-09-02T17:35:25+05:30
[INFO] [1m------------------------------------------------------------------------[m

Similarly for Gradle, you can run the following command to build the jar.

gradle clean build

Run Hello World with Java

Once you have created an executable JAR file, you can find it under the target directory. In our case it is in E: > Dev > demo > target > demo-0.0.1-SNAPSHOT.jar.

Now, run the JAR file by using the command java jar <JARFILE>. Observe that in the above example, the JAR file is named demo-0.0.1-SNAPSHOT.jar

E:\dev\demo\target>java -jar demo-0.0.1-SNAPSHOT.jar

Once you run the jar file, you can see the output in the console window as shown below −

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

 :: Spring Boot ::                (v3.3.3)

2024-09-02T17:42:38.623+05:30  INFO 4712 --- [demo] [           main] c.tutorialspoint.demo.DemoApplication    : Starting DemoApplication v0.0.1-SNAPSHOT using Java 21.0.2 with PID 4712 (E:\Dev\demo\target\demo-0.0.1-SNAPSHOT.jar started by Tutorialspoint in E:\Dev\demo\target)
2024-09-02T17:42:38.626+05:30  INFO 4712 --- [demo] [           main] c.tutorialspoint.demo.DemoApplication    : No active profile set, falling back to 1 default profile: "default"
2024-09-02T17:42:40.250+05:30  INFO 4712 --- [demo] [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port 8080 (http)
2024-09-02T17:42:40.266+05:30  INFO 4712 --- [demo] [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2024-09-02T17:42:40.266+05:30  INFO 4712 --- [demo] [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.28]
2024-09-02T17:42:40.320+05:30  INFO 4712 --- [demo] [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2024-09-02T17:42:40.322+05:30  INFO 4712 --- [demo] [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1574 ms
2024-09-02T17:42:40.943+05:30  INFO 4712 --- [demo] [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port 8080 (http) with context path '/'
2024-09-02T17:42:40.969+05:30  INFO 4712 --- [demo] [           main] c.tutorialspoint.demo.DemoApplication    : Started DemoApplication in 3.122 seconds (process running for 3.902)

Now, look at the console, Tomcat started on port 8080 (http). Now, go to the web browser and hit the URL http://localhost:8080/ and you can see the output as shown below −

Tomcat Started on Port 8080 (http).
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