Explain Spring MVC Annotations : @Component, @Repository, @Service

Spring MVC Annotations : @Component, @Repository, @Service

@Component

@Component tells the spring container to pick the bean while component-scanning is running. It is more generalized form of the annotations and can be used for any type of beans to inform the component-scanning mechanism. The declaration would look like

@Component("studentDAO")

public class StudentDAOImpl implements StudentDAO{

 public StudentDTO createStudent(){

 //code here

 }

}

In reality, @Component annotation is very rarely used since other specialized annotations  @Service, @Repository and @Controller can be used.

@Repository

@Repository is specialized implementation of @Component for indicating the Data Access Objects (DAO). Advantage of using the @Repository annotation, importing the DAOs into the DI container and also this annotation makes the unchecked exceptions (thrown from DAO methods) eligible for translation into Spring DataAccessException.

package aid.net.spring;



import org.springframework.stereotype.Component;

import org.springframework.stereotype.Repository;



//@Component("studentDAO") - This also correct

@Repository("studentDAO")

public class StudentDAOImpl implements StudentDAO{

     //code here

 }

}

@Service
This another specialized version of @Component to inform the spring component-scanning mechanism to load the service classes. These are introduced to in the spring framework to add any specific features to the service classes in the future. The declaration of @Service annotation would be:

package aid.net.spring;



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

import org.springframework.stereotype.Component;

import org.springframework.stereotype.Service;



//@Component("studentManager") - This also correct

@Service("studentManager")

public class StudentManagerImpl implements StudentManager{

     //code here

 }

}

Spring MVC Annotations Example

Here is the complete working example using the annotations explained in the above sections. This example uses the spring mvc annotations @Component, @Repository and @Service.

StudentDTO.java



package aid.net.spring;



public class StudentDTO {

 private String id;

 private String name;

 private String grade;

 public String getId() {

  return id;

 }

 public void setId(String id) {

  this.id = id;

 }

 public String getName() {

  return name;

 }

 public void setName(String name) {

  this.name = name;

 }

 public String getGrade() {

  return grade;

 }

 public void setGrade(String grade) {

  this.grade = grade;

 }

 public String toString(){

  StringBuffer buffer = new StringBuffer();

  buffer.append("\nStudent Id : " + this.id);

  buffer.append("\nStudent Name : " + this.name);

  buffer.append("\nStudent Grade : " + this.grade);

  return buffer.toString();

 }

}



StudentDAO.java



package aid.net.spring;



public interface StudentDAO {

 public StudentDTO createStudent();

}



StudentDAOImpl.java



package aid.net.spring;



import org.springframework.stereotype.Component;

import org.springframework.stereotype.Repository;



//@Component("studentDAO") - This also correct

@Repository("studentDAO")

public class StudentDAOImpl implements StudentDAO{

 public StudentDTO createStudent(){

  StudentDTO dto = new StudentDTO();

  dto.setId("001");

  dto.setName("Che");

  dto.setGrade("First");

  return dto;

 }

}



StudentManager.java



package aid.net.spring;



public interface StudentManager {

 public StudentDTO createStudent();

}



StudentManagerImpl.java



ackage aid.net.spring;



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

import org.springframework.stereotype.Component;

import org.springframework.stereotype.Service;



//@Component("studentManager") - This also correct

@Service("studentManager")

public class StudentManagerImpl implements StudentManager{

 @Autowired StudentDAO studentDAO;

 public StudentDTO createStudent(){

  return studentDAO.createStudent();

 }

}

applicationContext.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-3.2.xsd

    http://www.springframework.org/schema/context

    http://www.springframework.org/schema/context/spring-context-3.2.xsd">

 <context:component-scan base-package="aid.net" />

</beans>

MainApp.java



package aid.net.spring;



import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;



public class MainApp {



 public static void main(String[] args) {

  ApplicationContext applicationContext = new ClassPathXmlApplicationContext("aid/net/spring/applicationContext.xml");

  StudentManager manager = (StudentManagerImpl)applicationContext.getBean("studentManager");

  System.out.println((manager.createStudent()));

 }



}