3-2 Spring DI 흉내내기(2)

2. 객체 컨테이너(ApplicationContext) 만들기

객체 저장소

Main2.java

package com.fastcampus.ch3.diCopy2;

import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

class Car {}
class Truck extends Car {}
class SportsCar extends Car{}
class Engine {}

class AppContext {
    Map map; //객체 저장소

    AppContext(){
        try {
            Properties p = new Properties();
            p.load(new FileReader("config.txt"));

            //Properties에 저장된 내용을 Map에 저장
            map = new HashMap(p);

            //반복문으로 클래스 이름을 얻어서 객체를 생성해서 다시 map에 저장
            for(Object key : map.keySet()){
                Class clazz = Class.forName((String)map.get(key));
                map.put(key, clazz.newInstance());
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

    }
    Object getBean(String key){
        return map.get(key);
    }
}

public class Main2 {
    public static void main(String[] args) throws Exception {
        AppContext ac = new AppContext();
        Car car = (Car)ac.getBean("car");
        Engine engine = (Engine)ac.getBean("engine");
        System.out.println("car = " + car);
        System.out.println("engine = " + engine);

    }
}

3. 자동 객체 등록하기 - Component Scanning

@Component
1. 패키지 내의 모든 클래스를 읽어서 Set에 저장.
2. 패키지 내에 @Component붙은 클래스 찾기.
3. @Component가 붙어있으면 객체를 생성해서 map에 저장.

Main3.java

package com.fastcampus.ch3.diCopy3;

import com.google.common.reflect.ClassPath;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;
import org.springframework.stereotype.Component;

import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

@Component class Car {}
@Component class Truck extends Car {}
@Component class SportsCar extends Car{}
//@Component
class Engine {}

class AppContext {
    Map map; //객체 저장소

    AppContext(){
        map = new HashMap();
        doComponentScan();

    }

    private void doComponentScan() {
        try {
            //1. 패키지내의 클래스 목록을 가져온다.
            //2. 반복문으로 클래스를 하나씩 읽어와서 @Component이 붙어 있는지 확인
            //3. @Component가 붙어있으면 객체를 생성해서 map에 저장
            ClassLoader classLoader = AppContext.class.getClassLoader();
            ClassPath classPath = ClassPath.from(classLoader);

            Set<ClassPath.ClassInfo> set = classPath.getTopLevelClasses("com.fastcampus.ch3.diCopy3");

            for(ClassPath.ClassInfo classInfo : set){
                Class clazz = classInfo.load();
                Component component = (Component)clazz.getAnnotation(Component.class);
                if(component != null){
                    String id = StringUtils.uncapitalize(classInfo.getSimpleName());
                    map.put(id, clazz.newInstance());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();

        }
    }

    Object getBean(String key){
        return map.get(key);
    }
}

public class Main3 {
    public static void main(String[] args) throws Exception {
        AppContext ac = new AppContext();
        Car car = (Car)ac.getBean("car");
        Engine engine = (Engine)ac.getBean("engine");
        System.out.println("car = " + car);
        System.out.println("engine = " + engine);

    }
}