어노테이션·리플렉션·동적 프록시

cd java-src/advanced/08_reflection_proxy
javac -encoding UTF-8 *.java && java -Dstdout.encoding=UTF-8 Main

Class<?> c = MemberServiceImpl.class;
for (Field f : c.getDeclaredFields())
    System.out.printf("필드 %s %s @Inject=%b%n",
            f.getType().getSimpleName(), f.getName(), f.isAnnotationPresent(Inject.class));
for (Method m : c.getDeclaredMethods()) {
    Transactional t = m.getAnnotation(Transactional.class);
    System.out.printf("메서드 %s @Transactional=%s%n",
            m.getName(), t == null ? "없음" : "readOnly=" + t.readOnly());
}

필드   MemberMapper mapper  @Inject=true
메서드 find(인자 1개)  @Transactional=없음
메서드 transfer(인자 3개)  @Transactional=readOnly=false
메서드 transferAll(인자 2개)  @Transactional=없음
record 구성요소: [long id, java.lang.String name, int point]

Class<?> c = Class.forName("MemberServiceImpl");
Object svc = c.getDeclaredConstructor().newInstance();
Field f = c.getDeclaredField("mapper");
f.get(svc);                 // IllegalAccessException: private
f.setAccessible(true);
f.get(svc);                 // null (아직 주입 전)

Method find = c.getMethod("find", long.class);
find.invoke(svc, 1L);       // 안에서 NPE → InvocationTargetException

private 접근 실패: class Main cannot access a member of class MemberServiceImpl ...
setAccessible 후 mapper = null
find(Long) 없음 → 시그니처는 long.class 로 찾아야 합니다
invoke 예외: InvocationTargetException ← 원본 NullPointerException

List<String> logged = (List<String>) Proxy.newProxyInstance(
        Main.class.getClassLoader(), new Class<?>[]{List.class},
        (proxy, m, args) -> {
            System.out.println("  호출: " + m.getName() + Arrays.toString(args));
            return m.invoke(target, args);
        });
logged.add("a");
logged.size();

  호출: add[a]
  호출: add[b]
  호출: size[]
size() = 2
프록시 클래스: jdk.proxy2.$Proxy4, isProxyClass=true, instanceof List=true
클래스는 불가: java.util.ArrayList is not an interface

public interface MemberMapper {
    @Select("SELECT * FROM member WHERE id = #{id}")
    Member findById(@Param("id") long id);

    @Update("UPDATE member SET point = point + #{delta} WHERE id = #{id}")
    int addPoint(@Param("id") long id, @Param("delta") int delta);
}

Matcher mt = PARAM.matcher(sql);                  // #\{(\w+)}
while (mt.find()) {
    ordered.add(named.get(mt.group(1)));
    mt.appendReplacement(prepared, "?");
}
mt.appendTail(prepared);

mapper = MapperProxy[MemberMapper] (jdk.proxy2.$Proxy5)
  ==> Preparing: SELECT * FROM member WHERE id = ?
  ==> Parameters: [1]
findById(1) = Member[id=1, name=김철수, point=100]
  ==> Preparing: UPDATE member SET point = point + ? WHERE id = ?
  ==> Parameters: [25, 3]
addPoint(3, 25) = 1건 → Member[id=3, name=박민수, point=75]
findById(99) = null

RecordComponent[] comps = type.getRecordComponents();
for (int i = 0; i < comps.length; i++) {
    types[i] = comps[i].getType();
    vals[i] = row.get(comps[i].getName());     // 컬럼명 = 구성요소 이름
}
return type.getDeclaredConstructor(types).newInstance(vals);

MemberService svc = TxProxy.wrap(new MemberServiceImpl(mapper), MemberService.class, tx);
svc.transfer(1, 2, 30);      // BEGIN → COMMIT
svc.transfer(1, 99, 10);     // BEGIN → 예외 → ROLLBACK, 예외는 그대로 전달
svc.transferAll(1, 99);      // 안에서 this.transfer → 프록시 없음

(a) 정상 이체 1→2, 30점
  [TX] BEGIN
  [TX] COMMIT
    결과: Member[id=1, name=김철수, point=70], Member[id=2, name=이영희, point=230]
(b) 없는 회원에게 이체 1→99, 10점
  [TX] BEGIN
  [TX] ROLLBACK ← IllegalArgumentException
    예외 그대로 전달: 받는 회원 없음: 99
    결과: Member[id=1, name=김철수, point=70] (롤백으로 70점 유지)
(c) transferAll(1, 99): 안에서 this.transfer 호출
    예외: 받는 회원 없음: 99
    결과: Member[id=1, name=김철수, point=0] ← BEGIN 없이 실행되어 롤백되지 않음

Method impl = cls.getMethod(m.getName(), m.getParameterTypes());
Transactional t = impl.getAnnotation(Transactional.class);
if (t == null) return invoke(m, target, args);

MiniContainer container = new MiniContainer(tx)
        .register(new MapperFactory(db).create(MemberMapper.class), new MemberServiceImpl());
container.start();
MemberService svc = container.get(MemberService.class);

  등록: 프록시[interface MemberMapper]
  등록: MemberServiceImpl → 프록시로 감쌈
  주입: MemberServiceImpl.mapper ← 프록시[interface MemberMapper]
꺼낸 빈: 프록시[interface MemberService]
  [TX] BEGIN
  [TX] COMMIT