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JavaInterviewPoint

Java Development Tutorials

Spring Boot auto-configuration | @SpringBootApplication Annotation Example

October 10, 2018 by javainterviewpoint Leave a Comment

Spring Boot provides the @SpringBootApplication annotation [from Spring Boot 1.2.0] in order to enable auto-configuration feature, the @SpringBootApplication annotation performs the work of the three annotations @Configuration, @ComponentScan and @EnableAutoConfiguration.

  • @Configuration – Allows you to register beans or import additional configuration class
  • @ComponentScan – Enables Component scanning of the packages specified
  • @EnableAutoConfiguration – Enables Spring Boot’s auto-configuration feature

In short @SpringBootApplication annotation in equivalent to use @Configuration, @ComponentScan, @EnableAutoConfiguration annotations with their default configuration.

@SpringBootApplication Annotation parameters

@SpringBootApplication annotation takes up four optional parameters

  • exclude: This parameter excludes the list of the classes from the auto-configuration
  • excludeNames: This parameter excludes the list of fully qualified class names from the auto configuration
  • scanBasePackageClasses: This parameters provides the list of classes in the other packages to which has to be applied for scanning
  • scanBasePackages: This parameters provides the list of packages which has to be applied for scanning

Folder Structure:

SpringBootApplication

  1. Create a Maven project (maven-archetype-quickstart) “SpringBootApplication” and create a package for our source files “com.javainterviewpoint” under  src/main/java 
  2. Now add the following dependency in the POM.xml
    <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.javainterviewpoint</groupId>
    	<artifactId>SpringBootApplication</artifactId>
    	<version>0.0.1-SNAPSHOT</version>
    	<packaging>jar</packaging>
    
    	<name>SpringBootApplication</name>
    	<url>http://maven.apache.org</url>
    
    	<properties>
    		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    		<java.version>1.8</java.version>
    	</properties>
    
    	<parent>
    		<groupId>org.springframework.boot</groupId>
    		<artifactId>spring-boot-starter-parent</artifactId>
    		<version>2.0.2.RELEASE</version>
    	</parent>
    
    	<dependencies>
    		<dependency>
    			<groupId>org.springframework.boot</groupId>
    			<artifactId>spring-boot-starter-web</artifactId>
    		</dependency>
    	</dependencies>
    </project>
  3. Create the Java classes App.java and HelloController.java under com.javainterviewpoint folder.

The spring-boot-starter-parent is a special starter, it provides useful Maven defaults. Since we are developing a web application, we also need to add spring-boot-starter-web dependency.This will add dependencies such Tomcat, Jackson, Spring boot etc which are required for our application.

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@SpringBootApplication Annotation Example

Dependency Tree

[INFO] ------------------------------------------------------------------------
[INFO] Building SpringBootApplication 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-dependency-plugin:3.0.2:tree (default-cli) @ SpringBootApplication ---
[INFO] com.javainterviewpoint:SpringBootApplication:jar:0.0.1-SNAPSHOT
[INFO] \- org.springframework.boot:spring-boot-starter-web:jar:2.0.2.RELEASE:compile
[INFO]    +- org.springframework.boot:spring-boot-starter:jar:2.0.2.RELEASE:compile
[INFO]    |  +- org.springframework.boot:spring-boot:jar:2.0.2.RELEASE:compile
[INFO]    |  +- org.springframework.boot:spring-boot-autoconfigure:jar:2.0.2.RELEASE:compile
[INFO]    |  +- org.springframework.boot:spring-boot-starter-logging:jar:2.0.2.RELEASE:compile
[INFO]    |  |  +- ch.qos.logback:logback-classic:jar:1.2.3:compile
[INFO]    |  |  |  +- ch.qos.logback:logback-core:jar:1.2.3:compile
[INFO]    |  |  |  \- org.slf4j:slf4j-api:jar:1.7.25:compile
[INFO]    |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.10.0:compile
[INFO]    |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.10.0:compile
[INFO]    |  |  \- org.slf4j:jul-to-slf4j:jar:1.7.25:compile
[INFO]    |  +- javax.annotation:javax.annotation-api:jar:1.3.2:compile
[INFO]    |  +- org.springframework:spring-core:jar:5.0.6.RELEASE:compile
[INFO]    |  |  \- org.springframework:spring-jcl:jar:5.0.6.RELEASE:compile
[INFO]    |  \- org.yaml:snakeyaml:jar:1.19:runtime
[INFO]    +- org.springframework.boot:spring-boot-starter-json:jar:2.0.2.RELEASE:compile
[INFO]    |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.9.5:compile
[INFO]    |  |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.9.0:compile
[INFO]    |  |  \- com.fasterxml.jackson.core:jackson-core:jar:2.9.5:compile
[INFO]    |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.9.5:compile
[INFO]    |  +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.9.5:compile
[INFO]    |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.9.5:compile
[INFO]    +- org.springframework.boot:spring-boot-starter-tomcat:jar:2.0.2.RELEASE:compile
[INFO]    |  +- org.apache.tomcat.embed:tomcat-embed-core:jar:8.5.31:compile
[INFO]    |  +- org.apache.tomcat.embed:tomcat-embed-el:jar:8.5.31:compile
[INFO]    |  \- org.apache.tomcat.embed:tomcat-embed-websocket:jar:8.5.31:compile
[INFO]    +- org.hibernate.validator:hibernate-validator:jar:6.0.9.Final:compile
[INFO]    |  +- javax.validation:validation-api:jar:2.0.1.Final:compile
[INFO]    |  +- org.jboss.logging:jboss-logging:jar:3.3.2.Final:compile
[INFO]    |  \- com.fasterxml:classmate:jar:1.3.4:compile
[INFO]    +- org.springframework:spring-web:jar:5.0.6.RELEASE:compile
[INFO]    |  \- org.springframework:spring-beans:jar:5.0.6.RELEASE:compile
[INFO]    \- org.springframework:spring-webmvc:jar:5.0.6.RELEASE:compile
[INFO]       +- org.springframework:spring-aop:jar:5.0.6.RELEASE:compile
[INFO]       +- org.springframework:spring-context:jar:5.0.6.RELEASE:compile
[INFO]       \- org.springframework:spring-expression:jar:5.0.6.RELEASE:compile

HelloController.java

package com.javainterviewpoint;

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

@RestController
public class HelloController
{
    @GetMapping("/hello")
    public String hello()
    {
        return "Welcome to JavaInterviewPoint";
    }
}
  • We have created our HelloController under com.javainterviewpoint package
  • We have a single method in the controller
    • hello() – This method will send a response “Welcome to JavaInterviewPoint”

App.java

package com.javainterviewpoint;

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

@SpringBootApplication ()
public class App 
{
    public static void main( String[] args )
    {
        SpringApplication.run(App.class, args);
    }
}
  • @SpringBootApplication annotation does the work of @EnableAutoConfiguration, @Configuration and @ComponentScan annotations together

Output:

Select the Project –>Run As –> Run Configuration –>Maven –> New Configuration. In the Main tab, key in the Goals as “spring-boot:run” and click on Run.

Hit on the url : http://localhost:8080/hello

SpringBootApplication 1

Filed Under: Java, Spring Boot, Spring Tutorial Tagged With: @SpringBootApplication, auto-configuration, Spring Boot

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