[EDIT] コースのコントローラとビュー、ユーザーサービスを修正しました。

src/main/java/com/example/demo/app/domain/service/UserService.java

@@ -3,5 +3,8 @@ package com.example.demo.app.domain.service;
 import com.example.demo.app.presentation.form.UserForm;
 
 public interface UserService {
+    
 	void register(UserForm userForm);
+    
+    public void updateCourse(Long userId, Long courseId);
 }

src/main/java/com/example/demo/app/domain/service/impl/UserServiceImpl.java

@@ -57,6 +57,18 @@ public class UserServiceImpl implements UserService {
 
 	userRepository.save(userEntity);
 	}
+	
+	@Override
+	public void updateCourse(Long userId, Long courseId) {
+		UserEntity userEntity = userRepository.findById(userId).orElseThrow();
+		
+		CourseEntity courseEntity = courseRepository.findById(courseId).orElseThrow();
+		
+		userEntity.setCourseEntity(courseEntity);
+		
+		userRepository.save(userEntity);
+	}
+	
 }
 
 

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

@@ -1,13 +1,22 @@
 package com.example.demo.app.presentation.controller;
 
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
+import jakarta.servlet.http.HttpSession;
+
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
-import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
 
+import com.example.demo.app.domain.model.LoginModel;
+import com.example.demo.app.domain.model.UserModel;
 import com.example.demo.app.domain.service.CourseInfoService;
 import com.example.demo.app.domain.service.CourseService;
+import com.example.demo.app.domain.service.UserService;
 import com.example.demo.app.presentation.form.CourseForm;
 import com.example.demo.app.presentation.form.CourseInfoForm;
 
@@ -15,6 +24,7 @@ import lombok.RequiredArgsConstructor;
 
 
 @Controller
+@RequestMapping("/course")
 @RequiredArgsConstructor
 public class CourseController {
 	
@@ -22,31 +32,70 @@ public class CourseController {
     // エラーメッセージ用の定数フィールド
     private final static String SEVERE_ERROR_MESSAGE = "エラーが発生しました！";
 
-    // private final HttpSession httpSession;
+    private final HttpSession httpSession;
     private final CourseService courseService;
     private final CourseInfoService courseInfoService;
+    private final UserService userService;
     
     
     
-    @GetMapping("/select-course")
+    @PostMapping("/select/register")
-    public String select(Model model) {
+    public String showSelectCourse(@ModelAttribute UserModel userModel, Model model) {
     	
-    	//try {
+    	try {
+    		
+    		model.addAttribute("mode", "select");
     		model.addAttribute("courseList", CourseForm.convertFrom(courseService.findAll()));
     		model.addAttribute("courseInfoList", CourseInfoForm.convertFrom(courseInfoService.findAll()));
     		
     		return "select_course";
     		
-    	//} catch (Exception e) {
+    	} catch (Exception e) {
-//    		// ログイン情報の破棄
+    		// ログイン情報の破棄
-//            httpSession.invalidate();
+            httpSession.invalidate();
-//
+
-//            e.printStackTrace();
+            e.printStackTrace();
-//
+
-//            // エラーログ出力
+            // エラーログ出力
-//            LOGGER.log(Level.SEVERE, SEVERE_ERROR_MESSAGE, e);
+            LOGGER.log(Level.SEVERE, SEVERE_ERROR_MESSAGE, e);
-//            // エラー画面遷移
+            // エラー画面遷移
-//            return null;
+            return null;
-//    	}
     	}
+    }
+    
+    @PostMapping("/select/change")
+    public String showChangeCourse(Model model) {
+    	
+    	try {
+    		
+    		model.addAttribute("mode", "change");
+    		model.addAttribute("courseList", CourseForm.convertFrom(courseService.findAll()));
+    		model.addAttribute("courseInfoList", CourseInfoForm.convertFrom(courseInfoService.findAll()));
+    		
+    		return "select_course";
+    		
+    	} catch (Exception e) {
+    		// ログイン情報の破棄
+            httpSession.invalidate();
+
+            e.printStackTrace();
+
+            // エラーログ出力
+            LOGGER.log(Level.SEVERE, SEVERE_ERROR_MESSAGE, e);
+            // エラー画面遷移
+            return null;
+    	}
+    }
+    
+    @PostMapping("/change")
+    public String changeCourse(@RequestParam Long courseId) {
+    	
+    	LoginModel loginUser = (LoginModel) httpSession.getAttribute("loginUser");
+
+    	userService.updateCourse(loginUser.getUserId(), courseId);
+    	
+    	return "redirect:/menu";
+    }
+    
+    
 }

src/main/resources/templates/select_course.html

@@ -2,25 +2,41 @@
 <html xmlns:th="http://www.thymeleaf.org">
 <head>
 <meta charset="UTF-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.7/dist/css/bootstrap.min.css" rel="stylesheet">
 <title>コース選択</title>
 </head>
 <body>
 	
+	<h1>コース選択</h1>
+	<form th:action="@{/user/register}" th:object="${userForm}" method="post">
+	  <input type="hidden" th:field="*{userName}">
+	  <input type="hidden" th:field="*{mailAddress}">
+	  <input type="hidden" th:field="*{birthDate}">
+	  <input type="hidden" th:field="*{password}">
+	  <input type="hidden" th:field="*{secretQuestionId}">
+	  <input type="hidden" th:field="*{secretAnswer}">
+	  <input type="hidden" th:field="*{saving}">
+	  <input type="hidden" th:field="*{annualIncome}">
+	  <input type="hidden" th:field="*{monthlyBudget}">
+	  <input type="hidden" th:field="*{targetAmount}">
+	<button type="submit">確定</button>
 	<div class="accordion" id="accordionExample">
 	  <div class="accordion-item" th:each="course:${courseList}">
-	    <h2 class="accordion-header">
+	    <h2 class="accordion-header d-flex align-items-center">
-	      <button class="accordion-button" type="button" data-bs-toggle="collapse" data-bs-target="#collapseOne" aria-expanded="true" aria-controls="collapseOne">
+		  <input type="radio" name="courseId" th:value="${course.courseId}" class="form-check-input ms-3 me-2">
+	      <button class="accordion-button collapsed" type="button" data-bs-toggle="collapse" th:data-bs-target="'#collapse' + ${course.courseId}" aria-expanded="false" aria-controls="'collapse' + ${course.courseId}">
 			<span th:text="${course.courseName}"></span>
 	      </button>
 	    </h2>
-	    <div id="collapseOne" class="accordion-collapse collapse show" data-bs-parent="#accordionExample">
+	    <div th:id="'collapse' + ${course.courseId}" class="accordion-collapse collapse" data-bs-parent="#accordionExample">
 	      <div class="accordion-body">
 	        <span th:text="${course.description}"></span>
 			<table border="1">
 				<tr>
-					<th>カテゴリ名</th><tr>配分(%)</tr>
+					<th>カテゴリ名</th><th>配分(%)</th>
 				</tr>
-				<tr th:each="courseInfo:${courseInfoList}" th:if="course.courseId == courseInfo.courseId">
+				<tr th:each="courseInfo:${courseInfoList}" th:if="${course.courseId == courseInfo.courseId}">
 					<td th:text="${courseInfo.categoryName}"></td>
 					<td th:text="${courseInfo.allocationRatio}"></td>
 				</tr>
@@ -29,7 +45,8 @@
 	    </div>
 	  </div>
 	</div>
+	</form>
 	
-	
+	<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.7/dist/js/bootstrap.bundle.min.js"></script>
 </body>
 </html>