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How to enable auto component scanning in spring?


In general, we define all of our spring beans or components with xml based configurations and we inject all dependencies during the bean declarations. Spring container registers all beans or compenets as defined in the xml based configurations. Spring also allows you to define your spring beans and components using annotations as well. When you use annotations, spring provides flexibility to auto scan components and register with spring container. This page shows an example to enable auto component scan in spring.

You can annotate your services or DAOs with on of @Component, @Service, @Repository, or @Controller annotations. The details about each of these annotations will be covered in the next examples. If you specify the class with one of these annotations, the class is eligible for auto scan.

package com.java2novice.service;

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

import com.java2novice.dao.InventoryDao;

@Service("j2nInventoryService")
public class J2nInventoryService {

	@Autowired
	private InventoryDao inventoryDao;
	
	public void testInventoryServce(){
		System.out.println("Inside service class, testInventoryServce()");
		inventoryDao.printInventoryDaoStatus();
	}
}

package com.java2novice.dao;

import org.springframework.stereotype.Component;

@Component
public class InventoryDao {
	
	public void printInventoryDaoStatus(){
		System.out.println("Inside InventoryDao & status method");
	}
}

Here is the xml based configuration file, to enable component auto scanning include component-scan tag, and specify base-package. The base-package value should be package name and will be scanned for the components with in the packages and its sub-packages.

<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-3.0.xsd
	http://www.springframework.org/schema/context
	http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <context:component-scan base-package="com.java2novice" />
</beans>

Spring bean demo class:

package com.java2novice.test;

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

import com.java2novice.service.J2nInventoryService;

public class SpringDemo {

	public static void main(String a[]){
		String confFile = "applicationContext.xml";
		ConfigurableApplicationContext context 
									= new ClassPathXmlApplicationContext(confFile);
		J2nInventoryService inventoryService = 
							(J2nInventoryService) context.getBean("j2nInventoryService");
		inventoryService.testInventoryServce();
	}
}

Output:
Inside service class, testInventoryServce()
Inside InventoryDao & status method
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Knowledge Centre
When to use LinkedList or ArrayList?
Accessing elements are faster with ArrayList, because it is index based. But accessing is difficult with LinkedList. It is slow access. This is to access any element, you need to navigate through the elements one by one. But insertion and deletion is much faster with LinkedList, because if you know the node, just change the pointers before or after nodes. Insertion and deletion is slow with ArrayList, this is because, during these operations ArrayList need to adjust the indexes according to deletion or insetion if you are performing on middle indexes. Means, an ArrayList having 10 elements, if you are inserting at index 5, then you need to shift the indexes above 5 to one more.
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