[EDIT] 二次実装に伴う定数の追加と、AOPのクラスも定数クラスを参照するよう編集しました。

src/main/java/com/example/demo/aop/aspect/SessionCheckAspect.java

@@ -10,6 +10,7 @@ import org.aspectj.lang.annotation.Pointcut;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
 
+import com.example.demo.app.presentation.controller.pageproperty.SessionKeyword;
 import com.example.demo.exception.NoSessionException;
 
 
@@ -32,7 +33,7 @@ public class SessionCheckAspect {
 	public void checkSession() {
 		HttpSession session = request.getSession(false);
 
-		if (session == null || session.getAttribute("loginUser") == null) {
+		if (session == null || session.getAttribute(SessionKeyword.LOGIN_USER) == null) {
 			throw new NoSessionException("不正なログインです");
 		}
 

src/main/java/com/example/demo/aop/handler/GlobalExceptionHandler.java

@@ -12,6 +12,8 @@ import org.springframework.web.HttpRequestMethodNotSupportedException;
 import org.springframework.web.bind.annotation.ControllerAdvice;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 
+import com.example.demo.app.presentation.controller.pageproperty.PageReturnAttributeKeyword;
+import com.example.demo.app.presentation.controller.pageproperty.TransitionTargetPageNameKeyword;
 import com.example.demo.exception.NoSessionException;
 
 @ControllerAdvice
@@ -30,18 +32,18 @@ public class GlobalExceptionHandler {
 		LOGGER.log(Level.SEVERE, SEVERE_ERROR_MESSAGE_ILLEGAL_TRANSITION, e);
 
 		model.addAttribute(
-                "errorMessage",
+                PageReturnAttributeKeyword.ERROR_MESSAGE,
                 "システムエラーが発生しました。"
                 + "初めからやり直してください。");
 
-        return "redirect:/login";
+        return TransitionTargetPageNameKeyword.REDIRECT + TransitionTargetPageNameKeyword.LOGIN;
 		
 	}
 
 	@ExceptionHandler(HttpRequestMethodNotSupportedException.class)
 	public String handleBadRequestException(Model model, Exception e, HttpSession session) {
-		model.addAttribute("error", SEVERE_ERROR_MESSAGE_BAD_REQUEST);
-		model.addAttribute("status", HttpStatus.BAD_REQUEST.value());
+		model.addAttribute(PageReturnAttributeKeyword.ERROR, SEVERE_ERROR_MESSAGE_BAD_REQUEST);
+		model.addAttribute(PageReturnAttributeKeyword.STATUS, HttpStatus.BAD_REQUEST.value());
 
 		e.printStackTrace();
 
@@ -50,7 +52,7 @@ public class GlobalExceptionHandler {
 		System.out.println("session invalidated");
     	session.invalidate();
 
-		return "error";
+		return TransitionTargetPageNameKeyword.ERROR_HTML;
 	}
 	
 	@ExceptionHandler(Exception.class)
@@ -60,6 +62,6 @@ public class GlobalExceptionHandler {
 
 		System.out.println("session invalidated exception");
 		session.invalidate();
-		return "error";
+		return TransitionTargetPageNameKeyword.ERROR_HTML;
 	}
 }

src/main/java/com/example/demo/app/presentation/controller/GoalController.java

@@ -275,7 +275,7 @@ public class GoalController {
 		
 		int currentAmount = goalService.getCurrentAmount(userId);
 		
-		model.addAttribute("currentAmount", currentAmount);
+		model.addAttribute(PageReturnAttributeKeyword.CURRENT_AMOUNT, currentAmount);
 		
 		return TransitionTargetPageNameKeyword.GOAL_CREATE_HTML;
 	}

src/main/java/com/example/demo/app/presentation/controller/pageproperty/PageReturnAttributeKeyword.java

@@ -4,7 +4,8 @@ public class PageReturnAttributeKeyword {
 
 	public static final String ERROR_MESSAGE = "errorMessage";
 	public static final String MESSAGE = "message";
-	
+	public static final String ERROR = "error";
+	public static final String STATUS = "status";
 	
 	public static final String QUESTION_LIST = "questionList";
 	public static final String USER_FORM = "userForm";