j. Annotation Based Configuration - kimxavi/spring

Spring 2.5 부터 dependency injection 을 어노테이션을 이용해서 설정할 수 있도록 됐다. bean wiring을 XML로 하는 대신에 컴퍼넌트 클래스에 annotations을 써서 관련 클래스, 메쏘드, 필드 선언의 사용이 가능하다. 어노테이션 주입은 XML injection보다 먼저 수행된다. 그러므로, XML injection이 어노테이션 주입을 덮어쓴다. 어노테이션은 스프링 컨테이너의 기본 값이 아니다. 그래서, 사용하기 전에 스프링 설정 파일에 아래와 같이 사용 가능하게 해야한다.

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

   <context:annotation-config/>
   <!-- bean definitions go here -->

</beans>

context:annotation-config 가 설정되면, 코드의 어노테이션을 자동으로 찾아준다.

@ Required

이 어노테이션은 setter메소드에 적용된다. 설정 시점에 XML 설정 파일에 설정하도록 요구한다. 없으면 BeanInitializationException 예외가 발생한다. Student.java

package com.tutorialspoint;

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

public class Student {
   private Integer age;
   private String name;

   @Required
   public void setAge(Integer age) {
      this.age = age;
   }
   public Integer getAge() {
      return age;
   }

   @Required
   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      return name;
   }
}

MainApp.java

package com.tutorialspoint;

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

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");

      Student student = (Student) context.getBean("student");

      System.out.println("Name : " + student.getName() );
      System.out.println("Age : " + student.getAge() );
   }
}

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

   <context:annotation-config/>

   <!-- Definition for student bean -->
   <bean id="student" class="com.tutorialspoint.Student">
      <property name="name"  value="Zara" />

      <!-- try without passing age and check the result -->
      <!-- property name="age"  value="11"-->
   </bean>

</beans>

Property 'age' is required for bean 'student'

@Required한 요소를 세팅 안해서 위와 같이 예외가 발생한다.

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

   <context:annotation-config/>

   <!-- Definition for student bean -->
   <bean id="student" class="com.tutorialspoint.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>
   </bean>

</beans>

위와 같이 바꿔준다.

@Autowired

@Autowired 어노테이션은 어디에,어떻게 autowiring이 성취되는지 좋은 제어를 제공한다. XML 설정파일의 property를 제거하고 @Autowired를 setter 메소드에 사용할 수 있다. 메소드에서 byType autowiring으로 작동한다.

TextEditor.java

package com.tutorialspoint;

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

public class TextEditor {
   private SpellChecker spellChecker;

   @Autowired
   public void setSpellChecker( SpellChecker spellChecker ){
      this.spellChecker = spellChecker;
   }
   public SpellChecker getSpellChecker( ) {
      return spellChecker;
   }
   public void spellCheck() {
      spellChecker.checkSpelling();
   }
}

SpellChecker.java

package com.tutorialspoint;

public class SpellChecker {
   public SpellChecker(){
      System.out.println("Inside SpellChecker constructor." );
   }

   public void checkSpelling(){
      System.out.println("Inside checkSpelling." );
   }
   
}

MainApp.java

package com.tutorialspoint;

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

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");

      TextEditor te = (TextEditor) context.getBean("textEditor");

      te.spellCheck();
   }
}

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

   <context:annotation-config/>

   <!-- Definition for textEditor bean without constructor-arg  -->
   <bean id="textEditor" class="com.tutorialspoint.TextEditor">
   </bean>

   <!-- Definition for spellChecker bean -->
   <bean id="spellChecker" class="com.tutorialspoint.SpellChecker">
   </bean>

</beans>

@Autowired on Properties

setter 메소드를 제거하고 프로퍼티에 @Autowired를 사용할 수 있다. autowired 프로퍼티의 값을 property를 사용하여 전달할 때, 스프링은 자동으로 프로퍼티를 할당하고 값이나 레퍼런스를 전달한다. TextEditor.java

package com.tutorialspoint;

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

public class TextEditor {
   @Autowired
   private SpellChecker spellChecker;

   public TextEditor() {
      System.out.println("Inside TextEditor constructor." );
   }
   
   public SpellChecker getSpellChecker( ){
      return spellChecker;
   }
   
   public void spellCheck(){
      spellChecker.checkSpelling();
   }
}

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

   <context:annotation-config/>

   <!-- Definition for textEditor bean -->
   <bean id="textEditor" class="com.tutorialspoint.TextEditor">
   </bean>

   <!-- Definition for spellChecker bean -->
   <bean id="spellChecker" class="com.tutorialspoint.SpellChecker">
   </bean>

</beans>

@Autowired on Constructors

@Autowired를 생성자에 적용할 수도 있다. XML 파일의 bean에 constructor-arg가 없을지라도 bean이 생성될 때 autowiring 된다.

TextEditor.java

package com.tutorialspoint;

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

public class TextEditor {
   private SpellChecker spellChecker;

   @Autowired
   public TextEditor(SpellChecker spellChecker){
      System.out.println("Inside TextEditor constructor." );
      this.spellChecker = spellChecker;
   }

   public void spellCheck(){
      spellChecker.checkSpelling();
   }
}

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

   <context:annotation-config/>

   <!-- Definition for textEditor bean without constructor-arg  -->
   <bean id="textEditor" class="com.tutorialspoint.TextEditor">
   </bean>

   <!-- Definition for spellChecker bean -->
   <bean id="spellChecker" class="com.tutorialspoint.SpellChecker">
   </bean>

</beans>

@Autowired with (required=false) option

기본적으로 @Autowired는 @Required 어노테이션과 유사하게 의존성이 요구됨을 의미한다. 그러나 @Autowired(required=false)를 줌으로써 이러한 기능을 꺼줄 수가 있다.

@Qualifier

동일한 유형의 하나 이상의 빈을 생성하고 그 프로퍼티 중 하나만을 wire 할 때의 상황이 있을 수 있다. 이러한 경우, 혼란을 없애기 위해서 정확히 bean을 명시함으로써 @Qualifier를 @Autowired와 함께 사용할 수 있다.

Student.java

package com.tutorialspoint;

public class Student {
   private Integer age;
   private String name;

   public void setAge(Integer age) {
      this.age = age;
   }
   
   public Integer getAge() {
      return age;
   }

   public void setName(String name) {
      this.name = name;
   }
   
   public String getName() {
      return name;
   }
}

Profile.java

package com.tutorialspoint;

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

public class Profile {
   @Autowired
   @Qualifier("student1")
   private Student student;

   public Profile(){
      System.out.println("Inside Profile constructor." );
   }

   public void printAge() {
      System.out.println("Age : " + student.getAge() );
   }

   public void printName() {
      System.out.println("Name : " + student.getName() );
   }
}

MainApp.java

package com.tutorialspoint;

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

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");

      Profile profile = (Profile) context.getBean("profile");

      profile.printAge();
      profile.printName();
   }
}

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

   <context:annotation-config/>

   <!-- Definition for profile bean -->
   <bean id="profile" class="com.tutorialspoint.Profile">
   </bean>

   <!-- Definition for student1 bean -->
   <bean id="student1" class="com.tutorialspoint.Student">
      <property name="name"  value="Zara" />
      <property name="age"  value="11"/>
   </bean>

   <!-- Definition for student2 bean -->
   <bean id="student2" class="com.tutorialspoint.Student">
      <property name="name"  value="Nuha" />
      <property name="age"  value="2"/>
   </bean>

</beans>

Inside Profile constructor.
Age : 11
Name : Zara

@Qualifier("student1")로 명시했기 때문에 bean id="student1"가 세팅되었다.

JSR-250 Annotations

@PostConstruct, @PreDestroy, @Resource 어노테이션.

@PostConstruct and @PreDestroy Annotations

bean의 설치, 분해 정의에서 우리는 간단히 init-method 와/또는 destroy-method를 선언했다. @PostConstruct와 @PreDestroy를 사용해서 해당 콜백들을 대체할 수가 있다. HelloWorld.java

package com.tutorialspoint;
import javax.annotation.*;

public class HelloWorld {
   private String message;

   public void setMessage(String message){
      this.message  = message;
   }

   public String getMessage(){
      System.out.println("Your Message : " + message);
      return message;
   }
   @PostConstruct
   public void init(){
      System.out.println("Bean is going through init.");
   }
   @PreDestroy
   public void destroy(){
      System.out.println("Bean will destroy now.");
   }
}

MainApp.java

package com.tutorialspoint;

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

public class MainApp {
   public static void main(String[] args) {

      AbstractApplicationContext context = 
                          new ClassPathXmlApplicationContext("Beans.xml");

      HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
      obj.getMessage();
      context.registerShutdownHook();
   }
}

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

   <context:annotation-config/>

   <bean id="helloWorld" 
       class="com.tutorialspoint.HelloWorld"
       init-method="init" destroy-method="destroy">
       <property name="message" value="Hello World!"/>
   </bean>

</beans>

Bean is going through init.
Your Message : Hello World!
Bean will destroy now.

@Resource Annotation

필드와 setter메소드에 @Resource를 사용할 수 있다. @Resource 어노테이션은 주입되어지는 bean의 이름으로 해석되어지는 name 어트리뷰트에셔 가져온다. by-name autowiring의 의미로 알 수 있다.

package com.tutorialspoint;

import javax.annotation.Resource;

public class TextEditor {
   private SpellChecker spellChecker;

   @Resource(name= "spellChecker")
   public void setSpellChecker( SpellChecker spellChecker ){
      this.spellChecker = spellChecker;
   }
   public SpellChecker getSpellChecker(){
      return spellChecker;
   }
   public void spellCheck(){
      spellChecker.checkSpelling();
   }
}

만약 'name'이 정확히 명시 돼있지 않다면, 기본 이름은 필드명이나 setter 메소드를 근원으로 한다. 필드에 있을 때 필드명을 가져온다. setter에 있을 때 bean 프로퍼티 이름을 가져온다.

j. Annotation Based Configuration - kimxavi/spring_tutorial GitHub Wiki

@ Required

@Autowired

@Autowired on Properties

@Autowired on Constructors

@Autowired with (required=false) option

@Qualifier

JSR-250 Annotations

@PostConstruct and @PreDestroy Annotations

@Resource Annotation

⚠️ GitHub.com Fallback ⚠️

j. Annotation Based Configuration - kimxavi/spring_tutorial GitHub Wiki

@ Required

@Autowired

@Autowired on Properties

@Autowired on Constructors

@Autowired with (required=false) option

@Qualifier

JSR-250 Annotations

@PostConstruct and @PreDestroy Annotations

@Resource Annotation

⚠️ **GitHub.com Fallback** ⚠️

⚠️ GitHub.com Fallback ⚠️