Spring 4 - Auto Component scanning example

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Technologies used:   JDK 1.8.0_121 | Spring 4.3.5.RELEASE | Maven 3.9.9 | Eclipse Mars.2 (4.5.2)

Spring provides four stereotype annotations: @Component, @Controller, @Service and @Repository for spring-managed components.

The @Controller, @Service and @Repository annotations are specializations of the @Component annotation for more specific purpose in presentation, service and data access layer respectively.

In Spring framework, we can enable the auto component scanning by using

• The <context:component-scan/> element in XML based configuration
• The @ComponentScan annotation in java based configuration
• The AnnotationConfigApplicationContext#scan() method

Create Spring Components

Create an EmployeeService bean under com.boraji.tutorial.spring.service package as follows.

EmployeeService.java

package com.boraji.tutorial.spring.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.boraji.tutorial.spring.dao.EmployeeDao;

@Service
public class EmployeeService {

   @Autowired
   private EmployeeDao employeeDao;
   
   public void doSomething(){
      System.out.println("Inside EmployeeService's doSomething() method.");
      employeeDao.doSomething();
   }
}

Create an EmployeeDao bean under com.boraji.tutorial.spring.dao package as follows.

EmployeeDao.java

package com.boraji.tutorial.spring.dao;

import org.springframework.stereotype.Repository;

@Repository
public class EmployeeDao {

   public void doSomething() {
      System.out.println("Inside EmployeeDao's doSomething() method.");
   }
}

Enable component scanning using the <context:component-scan/> element

To enable auto component scanning in XML based configuration, use the <context:component-scan base-package=""/> element as follows.

Beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns:context="http://www.springframework.org/schema/context"
  xsi:schemaLocation="http://www.springframework.org/schema/beans 
  http://www.springframework.org/schema/beans/spring-beans.xsd
  http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-4.3.xsd">

  <context:component-scan
    base-package="com.boraji.tutorial.spring.service,
                  com.boraji.tutorial.spring.dao" />
</beans>

Run application.

MainApp.java

package com.boraji.tutorial.spring;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.boraji.tutorial.spring.service.EmployeeService;

/**
 * @author imssbora
 */
public class MainApp {
   public static void main(String[] args) {

      @SuppressWarnings("resource")
      ApplicationContext context1 = new ClassPathXmlApplicationContext("Beans.xml");
      EmployeeService service1 = context1.getBean(EmployeeService.class);
      service1.doSomething();

   }
}

Output

Inside EmployeeService's doSomething() method.
Inside EmployeeDao's doSomething() method.

Enable component scanning using the @ComponentScan annotation

To enable auto component scanning in java based configuration, annotate your @Configuration class as follows.

AppConfig.java

package com.boraji.tutorial.spring.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * @author imssbora
 */
@Configuration
@ComponentScan(basePackages = { "com.boraji.tutorial.spring.service",
      "com.boraji.tutorial.spring.dao" })
public class AppConfig {
   
}

Run application.

MainApp.java

package com.boraji.tutorial.spring;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.boraji.tutorial.spring.config.AppConfig;
import com.boraji.tutorial.spring.service.EmployeeService;

/**
 * @author imssbora
 */
public class MainApp {
   public static void main(String[] args) {

      @SuppressWarnings("resource")
      ApplicationContext context2=new AnnotationConfigApplicationContext(AppConfig.class);
      EmployeeService service2 = context2.getBean(EmployeeService.class);
      service2.doSomething();
   }
}

Output

Inside EmployeeService's doSomething() method.
Inside EmployeeDao's doSomething() method.

Enable component scanning using the scan() method of application context

Without using the XML or java based configuration, we can enable component scanning using the AnnotationConfigApplicationContext#scan() method as follows.

MainApp.java

package com.boraji.tutorial.spring;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.boraji.tutorial.spring.service.EmployeeService;

/**
 * @author imssbora
 */
public class MainApp {
   public static void main(String[] args) {

      AnnotationConfigApplicationContext context3 =
            new AnnotationConfigApplicationContext();
      
      context3.scan("com.boraji.tutorial.spring.service");
      context3.scan("com.boraji.tutorial.spring.dao");
      context3.refresh();
      
      EmployeeService service3 = context3.getBean(EmployeeService.class);
      service3.doSomething();
      context3.close();
   }
}

Output

Inside EmployeeService's doSomething() method.
Inside EmployeeDao's doSomething() method.