06. 서블릿 확장 API 사용하기

@WebServlet("/first")
public class FirstServlet
    extends HttpServlet {

    protected void doGet(
        HttpServletRequest request,
        HttpServletResponse response)
        throws ServletException, IOException {

        response.sendRedirect("second");
    }
}

// 첫 번째 서블릿 - 데이터 전달
response.sendRedirect(
    "second?name=lee&age=25");

// 두 번째 서블릿 - 데이터 수신
String name =
    request.getParameter("name");
String age =
    request.getParameter("age");

// 1초 후 second 서블릿으로 이동
response.addHeader(
    "Refresh", "1;url=second");

@WebServlet("/first")
public class FirstServlet
    extends HttpServlet {

    protected void doGet(
        HttpServletRequest request,
        HttpServletResponse response)
        throws ServletException, IOException {

        // 바인딩 - request에 데이터 저장
        request.setAttribute(
            "name", "홍길동");

        // dispatch - 서버 내부에서 전달
        RequestDispatcher dp =
            request.getRequestDispatcher(
                "second");
        dp.forward(request, response);
    }
}

@WebServlet("/second")
public class SecondServlet
    extends HttpServlet {

    protected void doGet(
        HttpServletRequest request,
        HttpServletResponse response)
        throws ServletException, IOException {

        // 바인딩된 데이터 수신
        String name = (String)
            request.getAttribute("name");

        response.setContentType(
            "text/html;charset=UTF-8");
        PrintWriter out =
            response.getWriter();
        out.println("이름: " + name);
    }
}

// 서블릿A - 리스트 바인딩 후 포워드
List<MemberVO> members =
    dao.selectAll();

request.setAttribute(
    "memberList", members);

RequestDispatcher dp =
    request.getRequestDispatcher(
        "/memberList.jsp");
dp.forward(request, response);

// memberList.jsp - 바인딩 데이터 수신
List<MemberVO> list =
    (List<MemberVO>)
    request.getAttribute("memberList");

for (MemberVO vo : list) {
    out.println(vo.getName());
}

<web-app>
    <context-param>
        <param-name>adminEmail</param-name>
        <param-value>admin@test.com</param-value>
    </context-param>
</web-app>

// 서블릿에서 조회
ServletContext ctx =
    getServletContext();
String email =
    ctx.getInitParameter("adminEmail");
// → admin@test.com

// 서블릿A - 데이터 바인딩
ServletContext ctx =
    getServletContext();
List<String> notices =
    Arrays.asList("공지1", "공지2");
ctx.setAttribute("notices", notices);

// 서블릿B - 데이터 조회 (다른 서블릿)
ServletContext ctx =
    getServletContext();
List<String> notices =
    (List<String>)
    ctx.getAttribute("notices");

@WebServlet(
    urlPatterns = "/init-test",
    initParams = {
        @WebInitParam(
            name = "email",
            value = "admin@test.com"),
        @WebInitParam(
            name = "tel",
            value = "010-1234-5678")
    }
)
public class InitParamServlet
    extends HttpServlet {

    protected void doGet(
        HttpServletRequest request,
        HttpServletResponse response)
        throws ServletException, IOException {

        // ServletConfig로 조회
        String email =
            getInitParameter("email");
        String tel =
            getInitParameter("tel");
    }
}

<servlet>
    <servlet-name>initServlet</servlet-name>
    <servlet-class>
        com.example.InitParamServlet
    </servlet-class>
    <init-param>
        <param-name>email</param-name>
        <param-value>admin@test.com</param-value>
    </init-param>
</servlet>

@WebServlet(
    name = "loadConfig",
    urlPatterns = "/config",
    loadOnStartup = 1
)
public class ConfigServlet
    extends HttpServlet {

    @Override
    public void init()
        throws ServletException {
        // 톰캣 시작 시 실행됨
        System.out.println(
            "설정 서블릿 초기화 완료");
    }
}

<servlet>
    <servlet-name>loadConfig</servlet-name>
    <servlet-class>
        com.example.ConfigServlet
    </servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>