Spring @ComponentScan tutorial

last modified October 18, 2023

Spring @ComponentScan tutorial shows how to enable component scanning in a Spring application. Component scanning enables auto-detection of beans by Spring container.

Spring is a popular Java application framework for creating enterprise applications.

Spring @ComponentScan

@ComponentScan annotation enables component scanning in Spring. Java classes that are decorated with stereotypes such as @Component, @Configuration, @Service are auto-detected by Spring. The @ComponentScan's basePackages attribute specifies which packages should be scanned for decorated beans.

The @ComponentScan annotation is an alternative to <context:component-scan> XML tag.

Spring @ComponentScan example

The application enables component scanning with @ComponentScan. We have one service bean that returns the current time.

pom.xml
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ └───service
│ │ TimeService.java
│ └───resources
│ logback.xml
└───test
 └───java

This is the project structure.

<?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.zetcode</groupId>
 <artifactId>componentscan</artifactId>
 <version>1.0-SNAPSHOT</version>
 <properties>
 <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 <maven.compiler.source>17</maven.compiler.source>
 <maven.compiler.target>17</maven.compiler.target>
 <spring-version>5.3.23</spring-version>
 </properties>
 <dependencies>
 <dependency>
 <groupId>ch.qos.logback</groupId>
 <artifactId>logback-classic</artifactId>
 <version>1.4.0</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-context</artifactId>
 <version>${spring-version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-core</artifactId>
 <version>${spring-version}</version>
 </dependency> 
 
 </dependencies>
 <build>
 <plugins>
 <plugin>
 <groupId>org.codehaus.mojo</groupId>
 <artifactId>exec-maven-plugin</artifactId>
 <version>3.1.0</version>
 <configuration>
 <mainClass>com.zetcode.Application</mainClass>
 </configuration>
 </plugin>
 </plugins>
 </build>
</project>

In the pom.xml file, we have basic Spring dependencies spring-core, spring-context, and logging logback-classic dependency.

The exec-maven-plugin is used for executing Spring application from the Maven on the command line.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
 <logger name="org.springframework" level="ERROR"/>
 <logger name="com.zetcode" level="INFO"/>
 <appender name="consoleAppender" class="ch.qos.logback.core.ConsoleAppender">
 <encoder>
 <Pattern>%d{HH:mm:ss.SSS} %blue(%-5level) %magenta(%logger{36}) - %msg %n
 </Pattern>
 </encoder>
 </appender>
 <root>
 <level value="INFO" />
 <appender-ref ref="consoleAppender" />
 </root>
</configuration>

The logback.xml is a configuration file for the Logback logging library.

package com.zetcode.service;
import org.springframework.stereotype.Service;
import java.time.LocalTime;
@Service
public class TimeService {
 public LocalTime getTime() {
 var now = LocalTime.now();
 return now;
 }
}

The TimeService class is annotated with the @Service annotation. It is registered by Spring as a managed bean with the help of component scanning.

package com.zetcode;
import com.zetcode.service.TimeService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@ComponentScan(basePackages = "com.zetcode")
@Configuration
public class Application {
 private static final Logger logger = LoggerFactory.getLogger(Application.class);
 public static void main(String[] args) {
 var ctx = new AnnotationConfigApplicationContext(Application.class);
 var timeService = (TimeService) ctx.getBean("timeService");
 logger.info("The time is {}", timeService.getTime());
 ctx.close();
 }
}

The application is annotated with @ComponentScan. The basePackages option tells Spring to look for components in the com/zetcode package and its subpackages.

var ctx = new AnnotationConfigApplicationContext(Application.class);

AnnotationConfigApplicationContext is a Spring standalone application context. It accepts the annotated Application as an input; thus the scanning is enabled.

var timeService = (TimeService) ctx.getBean("timeService");
logger.info("The time is {}", timeService.getTime());

We get the registered service bean and call its method.

$ mvn -q exec:java
10:57:01.912 INFO com.zetcode.Application - The time is 10:57:01.912235800

We run the application.

In this article we have enabled component scanning with @ComponentScan.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

List all Spring tutorials.