Spring Boot - Bootstrapping

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

Spring Initiapzer

One of the ways to Bootstrapping a Spring Boot apppcation is by using Spring Initiapzer. To do this, you will have to visit the Spring Initiapzer 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 apppcation.

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

Once you provided the Group, Artifact, Dependencies, Build Project, Platform and Version, cpck 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 
   http://maven.apache.org/xsd/maven-4.0.0.xsd">
   
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>jar</packaging>

   <name>demo</name>
   <description>Demo project for Spring Boot</description>

   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>1.5.8.RELEASE</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>

   <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
      <java.version>1.8</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

Once you download the project, unzip the file. Now your build.gradle file looks as shown below −

buildscript {
   ext {
      springBootVersion =  1.5.8.RELEASE 
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}
apply plugin:  java 
apply plugin:  ecppse 
apply plugin:  org.springframework.boot 

group =  com.tutorialspoint 
version =  0.0.1-SNAPSHOT 
sourceCompatibipty = 1.8

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 dependency

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

Main Method

The main method should be writing the Spring Boot Apppcation class. This class should be annotated with @SpringBootApppcation. This is the entry point of the spring boot apppcation 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.SpringApppcation;
import org.springframework.boot.autoconfigure.SpringBootApppcation;

@SpringBootApppcation
pubpc class DemoApppcation {
   pubpc static void main(String[] args) {
      SpringApppcation.run(DemoApppcation.class, args);
   }
}

Write a Rest Endpoint

To write a simple Hello World Rest Endpoint in the Spring Boot Apppcation 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 @RequestMapping annotation.

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

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

package com.tutorialspoint.demo;

import org.springframework.boot.SpringApppcation;
import org.springframework.boot.autoconfigure.SpringBootApppcation;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApppcation
@RestController

pubpc class DemoApppcation {
   pubpc static void main(String[] args) {
      SpringApppcation.run(DemoApppcation.class, args);
   }
   @RequestMapping(value = "/")
   pubpc String hello() {
      return "Hello World";
   }
}

Create an Executable JAR

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

Use the Maven command mvn clean install as shown below −

After executing the command, you can see the BUILD SUCCESS message at the command prompt as shown below −

Use the Gradle command gradle clean build as shown below −

After executing the command, you can see the BUILD SUCCESSFUL message in the command prompt as shown below −

Run Hello World with Java

Once you have created an executable JAR file, you can find it under the following directories.

For Maven, you can find the JAR file under the target directory as shown below −

For Gradle, you can find the JAR file under the build/pbs directory as shown below −

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

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

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 −