[Spring Boot] 2. Reflection_4.Ex04

Mar 20, 2025

Contents

1. Component Scan?Annotation / @Component Annotation / @RequestMapping DispatcherServlet UserController BoardController ex04 Package 안에 있는 Class 확인하기 App Component Annotation이 있는 Class 확인하기

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1. Component Scan?

@Component 계열 어노테이션이 붙은 클래스를 자동으로 감지하고 Spring 컨테이너에 등록하는 기능.

@Configuration 클래스에서 @ComponentScan을 사용해 설정할 수 있음.

2. 주요 Annotation

어노테이션	설명
`@Component`	가장 일반적인 컴포넌트 지정
`@Service`	서비스 계층(비즈니스 로직) 컴포넌트
`@Repository`	데이터 액세스 계층 (DAO) 컴포넌트
`@Controller`	Spring MVC 컨트롤러
`@RestController`	REST API 컨트롤러

⚡ 모든 어노테이션은 @Component를 기반으로 동작한다. 즉, @Service, @Repository, @Controller도 @Component의 기능을 포함하고 있다.

Annotation / @Component


package ex04;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME) // 언제 작동할지 정함 runtime or source(comfile시)
@Target(ElementType.TYPE) // 클래스 위!
public @interface Component {  // 이 깃발이 붙은 클래스만 new해서 전달

}

Annotation / @RequestMapping


package ex04;
//A회사

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME) // 언제 작동할지 정함 runtime or source(comfile시)
@Target(ElementType.METHOD)
public @interface RequestMapping {
    String value();
}

DispatcherServlet


package ex04;

import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.HashSet;
import java.util.Set;

public class DispatcherServlet {
    public Set<Object> componentScan(String packageName) {
// 1. @Component가 붙으면 new해서 컬렉션에 담기
        Set<Object> instances = new HashSet();

        ClassLoader classLoader = ClassLoader.getSystemClassLoader();
        URL packageUrl = classLoader.getResource(packageName);
        File packageDir = new File(packageUrl.getFile());

        for (File file : packageDir.listFiles()) {
            if (file.getName().endsWith(".class")) {
                String className = packageName + "." + file.getName().replace(".class", "");
                //System.out.println(className);

                try {
                    Class cls = Class.forName(className);
                    if (cls.isAnnotationPresent(Component.class)) {
                        Object instance = cls.getDeclaredConstructor().newInstance();
                        instances.add(instance);
                    }
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
            }
        } // for 종료
        return instances;
    }

    public void routing(Set<Object> instances, String path) {
        for (Object instance : instances) {
            Method[] methods = instance.getClass().getMethods();

            for (Method method : methods) {
                RequestMapping rm = method.getAnnotation(RequestMapping.class);

                if (rm == null) continue; // 다음 for문으로 바로 넘어감

                if (rm.value().equals(path)) {
                    try {
                        method.invoke(instance);
                    } catch (Exception e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        }

    }

}

UserController


package ex04;

@Component
public class UserController {
    @RequestMapping("/login")
    public void login() {
        System.out.println("login call");
    }

    @RequestMapping("/join")
    public void join() {
        System.out.println("join call");
    }

    @RequestMapping("/logout")
    public void logout() {
        System.out.println("logout call");
    }

    @RequestMapping("/userinfo")
    public void userinfo() {
        System.out.println("userinfo call");
    }
}

BoardController


package ex04;

@Component
public class BoardController {
    @RequestMapping("/write")
    public void write() {
        System.out.println("write call");
    }

    @RequestMapping("/delete")
    public void delete() {
        System.out.println("delete call");
    }

}

ex04 Package 안에 있는 Class 확인하기

‼️

실제 ex04 안에 있는 Class가 아닌 comfile된 Class를 찾는다

App


package ex04;

import java.io.File;
import java.net.URL;

public class App {
    public static void main(String[] args) {
        // 1. @Component가 붙으면 new해서 컬렉션에 담기
        ClassLoader classLoader = ClassLoader.getSystemClassLoader();
        URL packageUrl = classLoader.getResource("ex04");
        File packageDir = new File(packageUrl.getFile());

        for (File file : packageDir.listFiles()) {
            if (file.getName().endsWith(".class")) {
                String className = "ex04." + file.getName().replace(".class", "");
                System.out.println(className);
            }
        }
    }
}


C:\workspace\tools\jdk-21\bin\java.exe "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2024.3.2.1\lib\idea_rt.jar=54433:C:\Program Files\JetBrains\IntelliJ IDEA 2024.3.2.1\bin" -Dfile.encoding=UTF-8 -Dsun.stdout.encoding=UTF-8 -Dsun.stderr.encoding=UTF-8 -classpath C:\workspace\spring_lec\ref\out\production\ref ex04.App
ex04.App
ex04.BoardController
ex04.Component
ex04.DispatcherServlet
ex04.RequestMapping
ex04.UserController

Process finished with exit code 0

Component Annotation이 있는 Class 확인하기


package ex04;

import java.io.File;
import java.net.URL;
import java.util.HashSet;
import java.util.Set;

public class App {
    public static void main(String[] args) {
        // 1. @Component가 붙으면 new해서 컬렉션에 담기
        Set<Object> instances = new HashSet();

        ClassLoader classLoader = ClassLoader.getSystemClassLoader();
        URL packageUrl = classLoader.getResource("ex04");
        File packageDir = new File(packageUrl.getFile());

        for (File file : packageDir.listFiles()) {
            if (file.getName().endsWith(".class")) {
                String className = "ex04." + file.getName().replace(".class", "");
                //System.out.println(className);

                try {
                    Class cls = Class.forName(className);
                    if (cls.isAnnotationPresent(Component.class)) {
                        Object instance = cls.getDeclaredConstructor().newInstance();
                        instances.add(instance);
                    }
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
            }
        } // for 종료
        for (Object instance : instances) {
            System.out.println(instance.getClass().getName());
        }

    }
}

✅ 출력 결과


C:\workspace\tools\jdk-21\bin\java.exe "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2024.3.2.1\lib\idea_rt.jar=54455:C:\Program Files\JetBrains\IntelliJ IDEA 2024.3.2.1\bin" -Dfile.encoding=UTF-8 -Dsun.stdout.encoding=UTF-8 -Dsun.stderr.encoding=UTF-8 -classpath C:\workspace\spring_lec\ref\out\production\ref ex04.App
ex04.BoardController
ex04.UserController

Process finished with exit code 0