자바 Reflection API 언제쓰는건데!

@Component
public class MyFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

        //Request METHOD/URI 값 구하기
        HttpServletRequest http = (HttpServletRequest) request;
        String reqMethod = http.getMethod();  // GET
        String reqUri = http.getRequestURI(); // /hello
    }
}

@Component
public class MyFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

        // 1. Request METHOD/URI 값 구하기
        HttpServletRequest http = (HttpServletRequest) request;
        String reqMethod = http.getMethod();  // GET
        String reqUri = http.getRequestURI(); // /hello

        // 2. org.reflections 라이브러리 활용
        Reflections reflections = new Reflections(new ConfigurationBuilder()
                        .setUrls(ClasspathHelper.forJavaClassPath())
                        .addScanners(new TypeAnnotationsScanner(), new SubTypesScanner()));

        // 3. MyController 어노테이션이 붙은 모든 클래스 찾기
        Set<Class<?>> annotatedClasses = reflections.getTypesAnnotatedWith(MyController.class);
        for (Class<?> cls : annotatedClasses) {
            System.out.println("클래스: " + cls.getSimpleName()); //클래스: ApiController
        }
    }
}

//REST API 통신에서 사용될 클래스임을 알리기위한 어노테이션

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyController {
}

//특정 Http 요청을 담당할 메서드임을 알리기위한 어노테이션

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyMapping {
    String uri() default "/";
    String method() default  "GET";
}

//위의 두 어노테이션을 적용시킨 API 처리를 위한 로직

@MyController
public class ApiController {

    @MyMapping(uri = "/A", method = "GET")
    public String A(){
        return "A 비즈니스 로직 수행";
    }

    @MyMapping(uri = "/B", method = "GET")
    public String B(){
        return "B 비즈니스 로직 수행";
    }
}

@Component
public class MyFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        
        //Request METHOD/URI 값 구하기
        HttpServletRequest http = (HttpServletRequest) request;
        String reqMethod = http.getMethod();
        String reqUri = http.getRequestURI();

        Reflections reflections = new Reflections(new ConfigurationBuilder()
                .setUrls(ClasspathHelper.forJavaClassPath())
                .addScanners(new TypeAnnotationsScanner(), new SubTypesScanner()));

        // MyAnnotation 어노테이션이 붙은 모든 클래스 찾기
        Set<Class<?>> annotatedClasses = reflections.getTypesAnnotatedWith(MyController.class);
        for (Class<?> cls : annotatedClasses) {
            Method[] methods = cls.getDeclaredMethods();            for (Method method : methods) {                MyMapping anno = method.getAnnotation(MyMapping.class);                if (anno != null) {                    String myUri = anno.uri();                    String myMethod = anno.method();                    // @MyMapping 어노테이션 정보를 이용하여 Request요청을 처리해줄 메서드 찾기. 
                    try {                        if (reqUri.equals(myUri) && reqMethod.equalsIgnoreCase(myMethod)) {                            ApiController helloController = new ApiController();                            String resp = (String) method.invoke(helloController);
                            response.setContentType("text/plain; charset=UTF-8");  
                            PrintWriter out = response.getWriter();
                            out.print(resp); 
                            out.flush();  
                            out.close();  
                        }
                    } catch (Exception e) {
                        throw new ServletException("에러 발생", e);
                    }
                }
            }
        }
    }
}